Altered resting-state functional connectivity of the frontal-striatal circuit in elderly with apathy.

Apathy is defined as reduction of goal-directed behaviors and a common nuisance syndrome of neurodegenerative and psychiatric disease. The underlying mechanism of apathy implicates changes of the front-striatal circuit, but its precise alteration is unclear for apathy in healthy aged people. The aim of our study is to investigate how the frontal-striatal circuit is changed in elderly with apathy using resting-state functional MRI. Eighteen subjects with apathy (7 female, 63.7 ± 3.0 years) and eighteen subjects without apathy (10 female, 64.8 ± 3.0 years) who underwent neuropsychological assessment and MRI measurement were recruited. We compared functional connectivity with/within the striatum between the apathy and non-apathy groups. The seed-to-voxel group analysis for functional connectivity between the striatum and other brain regions showed that the connectivity was decreased between the ventral rostral putamen and the right dorsal anterior cingulate cortex/supplementary motor area in the apathy group compared to the non-apathy group while the connectivity was increased between the dorsal caudate and the left sensorimotor area. Moreover, the ROI-to-ROI analysis within the striatum indicated reduction of functional connectivity between the ventral regions and dorsal regions of the striatum in the apathy group. Our findings suggest that the changes in functional connectivity balance among different frontal-striatum circuits contribute to apathy in elderly.

Introduction

Apathy is defined as a state of diminished motivation and goal-directed behavior, not attributable to decreased level of consciousness, cognitive impairment or emotional distress [1] Apathy occurs frequently in several neurodegenerative and neuropsychiatric disorders, and affects global cognitive function and clinical outcome [2].

Investigations of apathy mainly in neuropsychiatric diseases have been tried to explain its neural substrate with anatomical and functional alterations of brain circuits using different neuroimaging modalities. In Alzheimer’s disease, apathy is associated with the atrophy of several brain regions, including the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) [3]. Parkinson’s disease with apathy showed dopaminergic denervation in the striatum, OFC, and posterior cingulate cortex [4], in addition to reduced gray matter density of the cingulate cortex and inferior frontal gyrus [5]. Other brain disorders with apathy such as stroke [6, 7], frontotemporal dementia [8], and depression [9] also showed anatomical and functional changes of the frontal region or striatum. Thus, the hypothesis that abnormalities within frontal-striatal circuits are relevant to apathy becomes prevailing.

The work of Levy and Dubois [10] proposed that symptoms of apathy can be divided into three subtypes of defects of processing; ‘emotional’, ‘cognitive’, and ‘auto-activation’. These subtypes were assumed to correspond to the role of different regions of the frontal-striatal circuit; (1) ‘emotional’ is associated with the limbic territory including OFC, ventromedial prefrontal cortex (vmPFC), and ventral striatum, and (2) ‘cognitive’ is with the associative territory including dorsolateral prefrontal cortex (DLPFC) and dorsal caudate nucleus, and (3) ‘auto-activation’ is with the medial prefrontal cortex including ACC and supplementary motor area (SMA). Recently Le Heron et al. [11] adapted this framework to three stages of the normal motivative behavior based on abundant anatomical, biological and functional studies. First, the value system including the ventral striatum, vmPFC, and OFC is actuated. Then, the mediating system including the ventral striatum and ACC activates the motor system including the dorsal striatum, SMA, and posterior mid cingulate cortex, which achieves goal-directed behaviors.

Apathy is observed in older adults with normal cognitive function, and its prevalence is increased with aging and reduces their quality of life. Brodaty et al. [12] demonstrated apathy prevalence increased in a cognitively normal elderly cohort over a 5-year period from 6% to 15.8%. Moreover, presence of apathetic state in elderly is considered as an early sign of cognitive decline [13], and linked to lower activity [14]. Few neuroimaging studies have attempted to cope with apathetic state in healthy elderly adults, and it remains unclear whether the neural bases of apathy in normal aged people is the same as those in the neuropsychiatric groups. One study for aged population, structural changes of gray matter in the right putamen and the frontal and temporal lobes were related to apathetic state [15]. Moreover, the severity of apathetic state during cognitive tasks was related to reduced activation in the medial superior frontal gyrus, and changed activity in the DLPFC and left striatum [16]. Bonnelle et al. [17] also described that the ACC might play an important role in apathetic behavior of healthy people using task-related fMRI analyses. These findings imply apathetic state in healthy subjects is also likely associated with dysfunction of the frontal-striatum circuit.

Resting-state functional MRI (rs-fMRI) delineates functional connectivity between distant brain regions based on synchronized low-frequency fluctuations of blood oxygen level dependent (BOLD) signal [18]. Rs-fMRI has been widely used in both healthy subjects and patients with various neurogenetic and neuropsychiatric disorders. In several rs-fMRI studies of apathy in patients with Parkinson’s disease [19] and Alzheimer disease [20] demonstrated reduction of functional connectivity among regions of functional connectivity of the frontal-striatal circuit. One rs-fMRI study of cognitively- normal aged people indicated decreased functional connectivity between the ventral striatum and frontal region in apathetic state [21]. These studies suggested that rs-fMRI is useful in assessing apathetic state in elderly.

Recent investigation of rs-fMRI about the frontal-striatal circuit have demonstrated that the segregated frontal-striatal loops influenced each other and information converges across the loops [22]. Haber [23] described anatomical evidence that communication across functionally distinct subregions of the striatum may occur for integrating information from parallel frontal-striatal functional modules for the development of goal-directed behaviors. It is presumed that change of the communication across subregions of the striatum is observed in the diseases affecting the frontal-striatal circuit. For example, Bell et al [24]. demonstrated the reduction of functional connectivity across striatal subdivision in Parkinson’s disease compared to healthy control.

In this study, we applied region of interest (ROI)-based analyses for detecting distinct patterns of functional connectivity with/within the striatum. Twelve seeds placed throughout the striatum, six in each hemisphere, described by Di Martino et al. [25] were used. These seeds were derived from previous studies of anatomical and functional subdivisions of the striatum, and each seed was related to classical parallel and integrative frontal-striatal loop [26]. We aimed to investigate the underlying mechanism of apathy related to disfunction of the frontal-striatum circuit in healthy subjects by the analyses with the multiple seeds in the striatum, and located the alterations of interaction and organization among the different frontal-striatum circuits in the elderly with apathy.

Materials and methods

Participants

We recruited subjects who voluntarily participated in the brain checkup system at Shimane Institute of Health Science, Izumo City, Shimane Prefecture, Japan. The health check included physical examination, detailed medical history, laboratory blood tests, neuropsychological assessment, and cranial MRI. A total of 335 people in the database were screened on their apathy levels and the exclusion criteria. Exclusion criteria were: current or past presence of neurological or psychiatric disorders; Mini-mental State Examination (MMSE) score less than 26 or dementia; obvious structural brain disorders; and head motion > 2.0 mm during the scan of rs-fMRI. Clinical MRIs were evaluated by a trained neurologist and neuroradiologist.

Finally, 18 people with apathy (7 females, age: 63.7 ± 3.0 years, rage 61–68) and 18 people without apathy (10 females, age: 64.8 ± 3.0, years, rage 60–69) matched for age, gender, and years of education were included. The study was conducted in accordance with the Declaration of Helsinki (1975, as revised in 2008) and the regulations of the Japanese Ministry of Health, Labour and Welfare, and approved by the ethical committee of the Shimane University School of Medicine. All subjects gave written informed consent to this study.

Neuropsychological and neuropsychiatric measures

Apathy level was evaluated with the Japanese version of the Apathy Scale (AS) [27, 28]. This scale consisted of 14 items and was used in a self-assessment style. The AS ranges from 0 to 42 and higher AS values indicate higher apathetic status. The cutoff point was determined on the basis of the previous report on Japanese stroke patients, and the scale displayed a high validity [28] (sensitivity 81.3%, specificity 85.3%) with a cutoff point of 16 among the participants. In this study, the apathy group was composed of 18 participants with the AS score of 16 point or more, and the participants in the non-apathy group had the AS score less than 16.

Furthermore, all participants conducted the following neuropsychological assessments: MMSE [29], Frontal Assessment Battery (FAB) [30], and Kohs Block Design Test (KOHS) [31]. Depressive symptoms were evaluated using the Japanese version of Zung’s self-rating depression scale (SDS) [32].

Image acquisition

Imaging data were acquired using a Siemens AG 1.5 T scanner. Using T2*-weighted gradient-echo spiral pulse sequence, we measured twenty axial slices parallel to the plane connecting the anterior and posterior commissures. (repetition time = 2000 msec, echo time = 35 msec, flip angle = 90°, scan order = interleave, matrix size = 64 × 64, field of view = 256 × 256 mm2, isotropic spatial resolution = 4 mm, slice thickness = 5 mm, gap = 1 mm). We underwent 5-minute rs-fMRI scan after it was directed that all subjects stayed awake and closed their eyes. After the functional scans, we measured T1-weighted images of the whole brain (192 sagittal slices, repetition time = 2170 msec, echo time = 3.93 msec, inversion time = 1100 msec, flip angle = 90°, matrix size = 256 × 256, field of view = 256 × 256 mm2, isotropic spatial resolution = 1 mm).

Data preprocessing

SPM12 (https://www.fil.ion.ucl.ac.uk/spm/software/spm12/, RRID:SCR_007037) was used for MRI data preprocessing. The first 10 functional images of each subject were discarded for magnetic field stabilization. The remaining 140 functional images were realigned to remove any artifacts from head movement and to correct for differences in image acquisition time between slices. Average of max head motions were 0.29 ± 0.19 mm for the apathy group and 0.30 ± 0.20 mm for the non-apathy group. Next, the functional images were normalized to the standard space defined by a template T1-weighted image and resliced with a voxel size of 3 × 3 × 3 mm3 to adjust the gray matter probability maps. After spatial smoothing was applied with the FWHM equal to 8 mm, temporal preprocessing was performed with the CONN toolbox (https://web.conn-toolbox.org/, RRID:SCR_009550). The denoising steps included regressions of six bulk motion parameters and their first-order derivatives, the five potential noise components estimated from the white matter and cerebrospinal fluid [33], the scrubbing outlier scans were identified based on ART with intermediate settings (97 percentiles in normative sample), and band-pass filtering of 0.008–0.09 Hz.

Selection of region of interest (ROI)

We adopted 12 striatum seeds, which were delineated by Di Martino et al [25]. Each seed was as follows: the inferior ventral striatum (VSi) (± 9, 9, -8), superior ventral striatum (VSs) (± 10, 15, 0), dorsal caudate (DC) (± 13, 15, 9), dorsal caudal putamen (DCP) (± 28, 1, 3), dorsal rostral putamen (DRP) (± 25, 8, 6), and ventral rostral putamen (VRP) (± 20, 12, -3). The radius of each ROIs was 3.5 mm. The bilateral pairs of seeds were combined into a single ROI in ROI-to-voxel analysis. In ROI-to-ROI analysis, all 12 seeds were independently considered as ROIs.

Functional connectivity analysis

Data analyses were carried out using the CONN toolbox. In the first-level analysis, we obtained ROI-to-voxel functional connectivity maps for each individual subject. This analysis produced z-score maps of positive and negative correlation coefficients for 6 striatal seeds and whole-brain voxels, combining homologous left and right ROIs to one seed. We also conducted an ROI-to-ROI analysis to examine functional connectivity between 12 ROIs within the striatum for each subject.

In the second-level analysis, at first, we conducted one-sample t-test of whole brain functional connectivity for 6 striatal ROIs across 36 participants to acquire the functional connectivity map. Then, to assess the differences in functional connectivity between the apathy and non-apathy group, we conducted two-sample t-test controlling for confounding factors including age and sex with the statistical threshold at the voxel level of p < 0.001 and the cluster level of p < 0.05 for false discovery rate (FDR). Moreover, we added a group comparison of the ROI-to-ROI analysis for the purpose of examining functional connectivity among 12 striatal ROIs with FDR correction of p < 0.05. Finally, we conducted similar group comparisons of ROI-to-voxel and ROI-to-ROI using SDS as an additional covariate, because apathy and depression share common clinical features and they show high correlation among neuropsychological tests.

Results

Demographic data

A total of 36 (17 female) healthy participants (mean age; 64.2 years, SD; 3.0) were assessed for study eligibility. We assigned 18 subjects to the apathy group and 18 subjects to the non-apathy group. Table 1 summarizes our subjects’ baseline demographic and neuropsychological data. Statistical analyses of demographic and neuropsychological data were performed using two-sample t tests. Fisher’s exact test was used to compare gender distribution across the samples. P values less than 0.05 were considered significant. There were no significant differences between the apathy and non-apathy group in age, sex, educational status, and cognitive test scores (including the MMSE, FAB, and KOHS). The apathy group’s mean depression score was higher than the non-apathy group (t = 6.18, p < 0.01).

Table 1

Demographic and clinical characteristics of the apathy and non-apathy groups.

	Apathy (n = 18)	Non-apathy (n = 18)	Statistics (p-value)
Age (years)	63.7 (3.0)	64.8 (3.0)	0.276
Sex (female)	7	9	0.738
Education (years)	12.2(2.0)	13.4(2.9)	0.148
MMSE	28.3 (1.7)	28.9 (1.4)	0.302
FAB	15.9 (1.8)	16.4 (1.3)	0.309
KOHS	99.1 (19.9)	105 (13.9)	0.277
AS	19.2 (2.1)	2.6 (1.7)	<0.001
SDS	38.6 (5.0)	28.2 (5.1)	<0.001

Note. Data are demonstrated as means (standard deviation). Abbreviations: FAB, Frontal Assessment Battery; KOHS, Kohs Block Design Test; AS, Apathy scale; SDS, Zung’s self-rating depression scale.

Functional connectivity

The functional connectivity map of 6 striatal ROIs across 36 participants was similar to a previous study [25] that demonstrated connectivity between striatum subdivisions and other cerebral regions such as the frontal cortex, parietal cortex, and temporal cortex. Fig 1A shows functional connectivity maps among the VRP, DC and whole brain, and comparisons between the apathy and non-apathy groups. The distribution of functional connectivity for each seed of striatum were similar, but slightly different, for each seed. We performed two-sample t-test to explore differences in whole brain functional connectivity between the apathy and non-apathy groups. The apathy group showed decreased functional connectivity between the bilateral VRP and the cluster of voxels in the right dorsal anterior cingulate cortex/ pre supplementary motor area, (dACC/pre SMA) (x = 9, y = 6, z = 39, voxels = 48, p = 0.008 for FDR) compared with the non-apathy group. Moreover, the functional connectivity between bilateral DC and the cluster of voxels in the left sensorimotor area (x = -51, y = -15, z = 42, voxels = 63, p = 0.0005 for FDR) was increased for the apathy group compared with the non-apathy group (Table 2). There were no significant group differences in the analyses of other seeds.

Fig 1

Changes of resting-state functional connectivity associated with apathy.

(A) Seed-tovoxel analysis. The upper row shows whole brain maps of functional connectivity with seeds of the VRP and DC. The lower row shows difference of the functional connectivity between the apathy and non-apathy group for the seeds of VRP and DC. Red and blue foci indicate areas showing significant positive and negative connectivity differences, respectively. (B) Group comparison of ROI-to-ROI analysis for 12 striatal seeds. The blue lines indicate decreased connectivity in the apathy group.

Table 2

Regions showing significant functional connectivity differences between groups.

seed		region	voxels	cluster size p-FDR	MNI coordinates
					x	y	z
ventral rostral putamen	A>NA	R dACC/pre SMA	48	0.008	9	6	39
dorsal caudate	A>NA	L sensorimotor	63	0.0005	-51	-15	+42

Abbreviations: A, Apathy; NA, non-Apathy; dACC, dorsal anterior cingulate cortex; pre SMA, pre supplementary motor area.

To investigate the effect of apathy on the laterality of functional connectivity between the basal ganglia and cerebral cortex, we conducted a two-way ANOVA with GROUP (apathy/non-apathy) and HEMISHPERE (the bilateral pairs of seeds), and the result did not show significant difference between the right and left striatum seeds.

We performed ROI-to-ROI analysis within the striatum and compared the functional connectivity between two groups (Fig 1B). Compared with the non-apathy group, the apathy group showed greater reduction of functional connectivity between the right VSs and right DCP (t = -3.22, p = 0.016 for FDR). Functional connectivity between the VSi and dorsal striatum was also reduced (ts < -2.35, ps < 0.042 for FDR) in the apathy group. Moreover, functional connectivity between the right VSi and left DC (t = -2.45, p = 0.0420 for FDR) was reduced after controlling for SDS to control for the effects of depression (t = -2.68, p = 0.06 for FDR).

Discussion

In the current study, we found that people with apathy showed decreased functional connectivity between the VRP and dACC/pre SMA, along with increased functional connectivity between the DC and left sensorimotor area compared with people without apathy. In addition, the functional connectivity between some of 12 striatal ROIs was decreased for the apathy group compared with the non-apathy group. These changes were observed after controlling for depression score. Our results indicate that functional disruption of frontal-striatal circuits is associated with apathetic state in the elderly, independent of depression.

The dACC has been considered to be an important component of the classic frontal-striatal circuit model such as the parallel loops model [34] and the recent interactive cortico-striatal system [35]. The dACC, which is also called anterior midcingulate cortex, [36] is specialized for monitoring of errors [37] and conflict [38], evaluating choice behavior, and regulation of an action [39]. Cumulative evidence suggests that the dACC represents a hub where information about reinforcers is linked to guide appropriate action. Consequently, appropriate activation of dACC results in self-generated movement or goal-directed behavior. Actually, the several previous studies demonstrated that the dysfunction of dACC is associated with apathetic state in healthy people [40]. Recent conceptual framework of cortico-striatal circuit have speculated that the connections between functionally different frontal areas involved in emotion, cognition and motor function and the striatum are segregated and overlapped, and their interactions enable to carry out goal-directed actions [41]. The projections of the striatum are topographically organized, such that the ventromedial area of striatum is connected to the limbic frontal area, the dorsolateral area of striatum is connected to the motor-related frontal area, and the intermediate area of striatum, to the dACC and DLPFC, which is related to cognitive process. Our study showed that people with apathy had decreased functional connectivity between the dACC and VRP which is corresponded to the ventromedial area of striatum. These results support the notion that apathetic state in aged people is associated with defects of emotional and/or cognitive mechanisms in the frontal-striatal circuit. One recent rs-fMRI study also revealed that apathetic state was associated with reduction of functional connectivity between the ventral striatum and dACC [42].

The SMA is considered as a part of the motor-related areas on the medial surface of cerebral hemisphere [43], which plays an important role in generation and control of movement. The pre SMA that is separated from classical SMA [44] is located in the rostral portion of Brodmann area 6. The pre SMA is involved in more complex motor and cognitive process associate with goal-directed behavior [45], whereas the SMA is more closely related to movement execution [46]. The anatomical and functional studies demonstrated that the pre SMA is connected to the premotor area, dACC, and DLPFC but not motor area [47], and is also connected to intermediate portion of the striatum [48, 49]. Thus the pre SMA was considered to be a component of cognitive system [50, 51]. To the best our knowledge, this is the first rs-fMRI study that demonstrated decreased functional connectivity between the VRP and pre SMA in people with apathy. This result implies that the VRP located in the relatively dorsal part of ventral striatum is more related to cognition than the VSi located in the ventral part of ventral striatum and generally used as a ROI of the ventral striatum.

Another finding of the present study was the reduction of functional connectivity among ROIs within the striatum in the apathy group compared to the non-apathy group. We found that functional connectivity was more severely impaired between the VSs and DCP. The DCP is situated in the most dorsolateral and caudal part among our defined ROIs and has connections to motor and premotor areas [41]. The VSs is located in the dorsolateral part of ventral striatum, and is considered as not only the region connected to limbic frontal area but also the region related to frontal area involved in cognition [52]. Previous anatomical and functional studies reported that the portion of ventral striatum corresponding to the VSs was projected from the lateral OFC, and was involved in reward-associated decision making [53], while the VSi was primarily associated with limbic areas including the medial OFC. Moreover our result showed that the VSi, which approximately corresponds to the nucleus accumbens, also showed reduction of functional connectivity with the dorsolateral regions of striatum connected with cognitive areas including DLPFC and dACC [25]. A few studies on apathy demonstrated anatomical and functional alterations within the striatum, for instance, diminished ventral striatum volume [54, 55] and decreased functional connectivity between nucleus accumbens and another striatum area [42], but these studies have not focused on direct connectivity between individual subdivisions of the striatum. Our result, together with other studies, suggests that apathetic state may be attributed to changes of the balance between dorsal and ventral striatum network.

Furthermore, the current study demonstrated increased functional connectivity between the DC and sensorimotor area in people with compared with people without apathy. The DC is located in dorsal area of the striatum, and is connected to cognitive prefrontal areas like dorsolateral prefrontal cortex. Several rs-fMRI studies for apathy demonstrated hyperconnectivity between the DLPFC and the superior parietal cortex in Alzheimer disease [20], between the superior frontal gyrus and the thalamus in Parkinson’s disease [56]. These regions are included in the salience and attentional/executive systems and their hyperconnectivity was speculated as compensatory phenomenon for dysfunction of other frontal-striatal systems. Our result also suggests that functional dysfunction in the cognitive system in apathy could activate motor function area for compensation.

We analyzed functional connectivity using the SDS sore as a covariate to minimize the effect of depression. Apathy and depression are often overlapped clinically, and their diagnostic criteria are partly common [57]. But recent studies indicated that frontal-striatal circuit of apathy was separated from the network for depression. Several studies demonstrated that people with apathy had decreased functional connectivity associated with frontal-striatal circuit, whereas depressive people had increased functional connectivity with similar region reciprocally, such as between the dACC and other salience area [40], between caudate and thalamus, and between DFC and parahippocampal cortex [58]. In the present study, only when ROI-to-ROI analysis within the striatum was performed, significant difference in functional connectivity in the apathy group survived after controlling for SDS.

We have some limitations in the current study. We examined apathetic state using the AS, but the scale was not configured for classification of apathy subtype, and some questionnaire items overlapped with the SDS. A multidimensional scale has been recently developed to assess the subtypes of apathy [59]. Using such an assessment tool, we might delineate the various frontal-striatal circuits related to subtypes of apathy. Moreover, to ensure that the participants were clearly independent of depression, an apathy group without depression should have been included.

In addition, our subjects were aged people without neurodegenerative and psychiatric diseases, but apathy prevalence is lower in cognitively normal cohort than patient groups (such as, dementia) [60]. Specificity and similarity of apathetic state associated with healthy people and diseases have been unclear. Further studies about apathetic state of healthy people should address this issue.

In conclusion, our findings showed that apathetic state in aged people was associated with altered resting-state functional connectivity with/within the striatum, specifically decreased functional connectivity of the striatum with emotional and cognitive frontal-striatal circuits, and between ventral and dorsal regions within the striatum. These results suggest that alteration of interaction and organization among different frontal-striatum circuits contributes to apathy in elderly.

26 Jul 2021

PONE-D-21-12168

Altered resting-state functional connectivity of the frontal-striatal circuit in elderly with apathetic state

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Reviewer #1: The present study compared resting state striatal functional connectivity between the apathy and non-apathy groups. The connectivity between the ventral rostral putamen and the right dorsal anterior cingulate cortex/supplementary motor area was found decreased in the apathetic group while the connectivity between the dorsal caudate and the left sensorimotor area was increased. The ROI-to-ROI analysis revealed reduction of functional connectivity between the ventral regions and dorsal regions of the striatum in the apathy group. These results may help us to under stand the neural alteration associated with apathy. This reviewer has several concerns as below.

The description of data preprocessing on page 8 is not clear. The phrase of ‘scrubbing parameter with a band-pass filter of 0.01-0,08Hz’ is confusing. Considering the later sentence stated that the scrubbing parameter was used to identify the outlier scans, did the authors want to express in the first sentence that a band pass filtering was used and a scrubbing strategy was used to cutoff outlier scans using a ‘parameter’ generated by the toolbox? If so, what parameter and threshold was used to determine an outlier scan? For example, the frame-displacement (FD >0.5mm) was used in many previous studies.

The description of “functional connectivity analysis” is not clear. It was said that ‘In the first-level analysis, a multiple regression analysis was performed for each individual subject using the general linear model for correlation connectivity estimation’. My understanding of the procedure is that ‘the multiple regression analysis’ was used in the preprocessing stage to regress out nuisance variables including head motions and others. Then the resultant errors were band-pass filtered. The time course of each seed mask was extracted and correlated with the time course of each voxel. The correlation coefficients were then transferred with Fisher’s Z-transformation.

The FWHM of 8 mm seem too big as the seed ROIs are close to each other. In literature, 5 or 6mm is a typical FWHM and may be more proper for the current study.

The left and right homologous ROIs were combined to one seed when calculating functional connectivity maps. But the human brain laterization is well known. It’s better to conduct a 2-by-2 ANOA for the second level analysis with GROUP and HEMISHPERE as factors.

When reporting results, the functional connectivity of several seeds seems to have no difference between the two groups. But it was not explicitly stated.

The readability of Figure 2b is poor. I suggest a different font color or change the back groud color.

Reviewer #2: I understand from this manuscript that elderly individuals with apathy show decreased functional connectivity between the striatal structures (i.e., ventral rostral putamen), and frontal areas (i.e., dACC/pre SMA). Besides, increased functional connectivity between the striatal structures (i.e., dorsal caudate) and sensorimotor area was reported in elderly individuals with apathy as compared to elderly individuals without apathy.

Functional neuroanatomy studies are important for a better understanding of apathy which increases disability and caregiver burden in elderly population. This is a powerful study in terms of using fMRI analysis methods. I think if the authors strengthen the presentation of their study, it will contribute to the literature and colleagues of the field.

Major points:

1) The areas associated with apathy in AD are not just the ACC and OFC, or the entire ACC or OFC. If it is desired to exemplify some of the related brain regions, it may be more appropriate to reconstruct the sentence (Introduction section- Line 26).

2) 7th reference seems to be missing in the main text.

3) Extended sentences with conjunctions make it difficult to follow, and in some there may be errors in tense suffixes. In this sense, I would suggest that the manuscript be reviewed by the authors.

4) The authors may consider to edit the flow of Introduction section. The paragraph starting with "Apathy is also observed in older adults with..." from line 43 does not seem to be compatible with the previous paragraph. In the previous paragraph, the conceptualization of the apathy and the functional neuroanatomical correlates corresponding to this conceptualization are presented. However, the first sentence containing the word "also" causes the expectation for continuum of a topic.

5) I think, the first paragraph of the Materials and Methods/Participants section also need to be reconsidered. Especially these two sentences are hard to follow: "335 people in the database were screened on the levels of apathy and the exclusion criteria. Exclusion criteria were: current or past presence of neurological or psychiatric disorders such as cerebrovascular disease, Mini-mental State Examination (MMSE) score less than 26 or dementia, diffuse or multiple cerebral white matter lesions on T2-weighted image, obvious cerebral atrophy, head motion > 2.0 mm during the scan of rs-fMRI". Since this section contains basic information for readers to understand the study, I think it would be more useful to give it in simpler sentences.

6) It is not common to use cut-off points on apathy scales. In general higher scores indicate higher levels of apathy. Was the cut-off point for the apathy scale used in a single study? Are there any other examples in recent studies, supporting the validation of this cut-off score other than the relevant reference (#32)?

7) Explaining the scoring of depression scale will make it possible to understand the results and the table. Does this depression scale involves any cognitive tasks? If not, I would strongly recommend not to cluster depression scale under the neuropsychological assessment.

8) Line 151. Giving an analysis result and comparative reference information in the Method section may not be very appropriate. I recommend to relocate that sentence to Discussion.

9) Under the figure: A)... Red and blue foci indicate areas showing significant positive and negative connectivity.

It is better to clarify the color and connectivity direction.

10) Creating a table with peak Talairach coordinates for ROIs can make it easier for the readers to understand the results. It will also be convenient for the study to be repeated by other researchers.

11) The authors drew attention to the overlap in symptoms of apathy and depression. However, if apathy and depression comorbidly present; it may not be easy to draw a line between these two syndrome as we can do between an internal disease and a psychiatric condition. It is known that both depression and apathy are the neuropsychiatric conditions that have independent effects on the molecular structure and physiological functioning of the brain. Statistically controlling the depression score may not result with subtracting the effect of depression from the brain activation as intended here in this study. I find the study's functional imaging analysis approach correct (controlling depression by adding the scores to analysis as covariant). However, adding multi covariates in fMRI analysis may suppress the overall activation which can cause underestimating the findings. In my opinion, in order to be able to say that the results were clearly independent of depression, a group of apathetic participants without depression should have been included. I would recommend the authors to discuss their method and findings stronger, in this context. Also, if the researchers have used any other tools or measurements, those can be included to manuscript in terms of increasing internal consistency.

Minor points:

Line 41. Mistyping of striatum as stratum

Line 60. I would suggest using "study of cognitively normal aged people" instead of "study of cognitive- normal aged people"

Line 85. I would suggest using "cranial MRI" instead of "head MRI"

Line 104. This long sentence "Furthermore, all participants conducted the following neuropsychological assessments: Cognitive functions, assessed by the MMSE [29], the Frontal Assessment Battery (FAB) [30], and the Kohs Block Design Test (KOHS) [31]; depressive symptoms were evaluated using the Japanese version of Zung’s self-rating depression scale (SDS) [32]." can be simply expressed like "Furthermore, all participants conducted the following neuropsychological assessments: MMSE [29], Frontal Assessment Battery (FAB) [30], and Kohs Block Design Test (KOHS) [31]. Depressive symptoms were evaluated using the Japanese version of Zung’s self-rating depression scale (SDS)"

Line 126. Could the authors have meant "adjust" by using the phrase "to agree with" in this sentence: Next, the functional images were normalized to the standard space defined by a template T1-weighted image and resliced with a voxel size of 3x3x3 mm3 to agree with the gray matter probability maps.

Line 209. If the intended meaning is not the process of aging; authors may consider using "elderly" instead of using the expression "aged people".

**********

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11 Oct 2021

Satoshi Ikemoto

Academic Editor

PLOS ONE

U.S. Headquarters

1265 Battery Street, Suite 200

San Francisco, CA 94111 United States

Re: Manuscript ID: PONE-D-21-12168

Dear Prof. Ikemoto,

Thank you very much for your e-mail and review of our manuscript (PONE-D-21-12168) entitled “Altered resting-state functional connectivity of the frontal-striatal circuit in elderly with apathy”. We also appreciate the reviewers taking the time to offer us your comments and insights related to the paper. In the following sections, you will find our responses to each of your points and suggestions.

Journal requirements:

Q1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf.

A1. We appreciate the helpful suggestion regarding Journal requirements. As suggested, we confirmed PLOS ONE's style requirements and corrected the whole manuscript accordingly.

Q2. Please consider rephrasing "apathetic people" to "patients/people with apathy", as our submission guidelines (http://journals.plos.org/plosone/s/submission-guidelines) suggest changing potentially stigmatizing labels should be changed to more current, acceptable terminology.

A2. We accept these journal requirements. The suggested key terms have been changed throughout the manuscript, title, and short title.

Q3. We note that Figures A & B in your submission contain copyrighted images. All PLOS content is published under the Creative Commons Attribution License (CC BY 4.0), which means that the manuscript, images, and Supporting Information files will be freely available online, and any third party is permitted to access, download, copy, distribute, and use these materials in any way, even commercially, with proper attribution. For more information, see our copyright guidelines: http://journals.plos.org/plosone/s/licenses-and-copyright.

A3. Thank you for this comment. Figures A & B in our submission are original figures. While our figures (especially Figure B) are indeed inspired by a previous study (Bell et al., 2015), we present that the only similarity between the figures is in the shape of the basal ganglia, and that there is no copyright on this shape, which reflects a generally accepted fact. We also present that the way Figure A is presented is completely typical and common.

Reference

Peter Bell et al. (2015) Dopaminergic basis for impairments in functional connectivity across subdivisions of the striatum in Parkinson's disease. Hum Brain Mapp. 2015 Apr;36(4):1278-91. doi: 10.1002/hbm.22701

Q4. We noticed you have some minor occurrence of overlapping text with the following previous publication(s), which needs to be addressed:

-https://direct.mit.edu/jocn/article/24/11/2186/27852/Decreased-Functional-Connectivity-by-Aging-Is

In your revision ensure you cite all your sources (including your own works), and quote or rephrase any duplicated text outside the methods section. Further consideration is dependent on these concerns being addressed.

A4.

We thank the editor for pointing this out and also recognize that this point is something that needs to be improved in our paper. Accordingly, we have tried to paraphrase as much as possible.

Reviewers' comments:

Reviewer #1: The present study compared resting state striatal functional connectivity between the apathy and non-apathy groups. The connectivity between the ventral rostral putamen and the right dorsal anterior cingulate cortex/supplementary motor area was found decreased in the apathetic group while the connectivity between the dorsal caudate and the left sensorimotor area was increased. The ROI-to-ROI analysis revealed reduction of functional connectivity between the ventral regions and dorsal regions of the striatum in the apathy group. These results may help us to understand the neural alteration associated with apathy. This reviewer has several concerns as below.

Comment: The description of data preprocessing on page 8 is not clear. The phrase of ‘scrubbing parameter with a band-pass filter of 0.01-0.08 Hz’ is confusing. Considering the later sentence stated that the scrubbing parameter was used to identify the outlier scans, did the authors want to express in the first sentence that a band pass filtering was used and a scrubbing strategy was used to cutoff outlier scans using a ‘parameter’ generated by the toolbox? If so, what parameter and threshold was used to determine an outlier scan? For example, the frame-displacement (FD > 0.5 mm) was used in many previous studies.

Response: Thank you for your comment. We fixed the description as follows:

Page 8 Line 129

…, the scrubbing outlier scans were identified based on ART with intermediate settings (97 percentiles in normative sample), and band-pass filtering of 0.08–0.09 Hz.

supplementation: The number of the band-pass filter was wrong and we made the necessary modifications.

Comment: The description of “functional connectivity analysis” is not clear. It was said that ‘In the first-level analysis, a multiple regression analysis was performed for each individual subject using the general linear model for correlation connectivity estimation’. My understanding of the procedure is that ‘the multiple regression analysis’ was used in the preprocessing stage to regress out nuisance variables including head motions and others. Then the resultant errors were band-pass filtered. The time course of each seed mask was extracted and correlated with the time course of each voxel. The correlation coefficients were then transferred with Fisher’s Z-transformation.

Response: Thank you for this comment. Your summarization is true. We fixed the description as follows:

Page 9 Line 141

Data analyses were carried out using the CONN toolbox. In the first-level analysis, we obtained ROI-to-voxel functional connectivity maps for each individual subject. This analysis produced z-score maps of positive and negative correlation coefficients between 6 striatal seeds and the whole-brain voxels, combining homologous left and right ROIs to one seed. We also conducted an ROI-to-ROI analysis to examine functional connectivity between 12 ROIs within the striatum for each subject.

Comment: The FWHM of 8 mm seem too big as the seed ROIs are close to each other. In literature, 5 or 6mm is a typical FWHM and may be more proper for the current study.

Response: Thank you for mentioning this important point. The reason for using the large FWHM in the present analysis is that the interest of this analysis is in the functional connectivity of the frontal robe. It is known that functional connectivity in the frontal robe shows large individual differences (Mueller et al., 2013). Therefore, we decided that 8-mm is appropriate enhance sensitivity of the analysis in this study. To confirm this, we conducted the additional analysis using the data smoothed with 6 mm FWHM. As a result, the right dorsal anterior cingulate cortex/ pre supplementary motor area, which showed significant group difference with the 8 mm FWHM, did not meet the criteria for significance with 6 mm FWHM. Thus, a comparably wide FWMH may be useful when investigating functional connectivity of the frontal lobe with the basal ganglia as a seed, due to the large individual variability.

Comment: The left and right homologous ROIs were combined to one seed when calculating functional connectivity maps. But the human brain laterization is well known. It’s better to conduct a 2-by-2 ANOA for the second level analysis with GROUP and HEMISHPERE as factors.

Response: Thank you for this advice. Follow the reviewer’s suggestion, to check the effect of apathy on laterality of functional connectivity between basal ganglia and cerebral cortex, we conducted a two-way ANOVA with GROUP (apathy/non-apathy) and HEMISHPERE (the bilateral pairs of seeds), and the result did not show significant difference between right and left striatum seeds. We have added this result to our Results section as follows.

Page 12 Line 185

To investigate the effect of apathy on the laterality of functional connectivity between the basal ganglia and cerebral cortex, we conducted a two-way ANOVA with GROUP (apathy/non-apathy) and HEMISHPERE (the bilateral pairs of seeds), and the result did not show significant difference between the right and left striatum seeds.

Comment: When reporting results, the functional connectivity of several seeds seems to have no difference between the two groups. But it was not explicitly stated.

Response: Thank you for this comment. We fixed the description as follows:

Page 12 Line 184

There were no significant group differences in the analyses of other seeds.

Comment: The readability of Figure 2b is poor. I suggest a different font color or change the background color.

Response: Thank you for this advice. We changed the background color of Figure 2b accordingly.

Reviewer #.2:

Major points:

Q1. The areas associated with apathy in AD are not just the ACC and OFC, or the entire ACC or OFC. If it is desired to exemplify some of the related brain regions, it may be more appropriate to reconstruct the sentence (Introduction section- Line 26).

A1. The reviewer is correct and we have corrected the sentence appropriately as follows:

In Alzheimer's disease, apathy is associated with the atrophy of several brain regions, including the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC)[3].

supplementation: About the third reference, we replaced the original reference, since we were citing a different reference previously.

Q2..7th reference seems to be missing in the main text.

A2. As indicated, the 7th reference has been added in the main text.

Q3. Extended sentences with conjunctions make it difficult to follow, and in some there may be errors in tense suffixes. In this sense, I would suggest that the manuscript be reviewed by the authors.

A3. We revised the entire paper and tried to use the shortest sentences possible. Additionally, although we hired a proofreading service prior to the initial submission of our manuscript, we have had our manuscript rechecked for publication. We will attach a certification for the resubmission.

Q4. The authors may consider to edit the flow of Introduction section. The paragraph starting with "Apathy is also observed in older adults with..." from line 43 does not seem to be compatible with the previous paragraph. In the previous paragraph, the conceptualization of the apathy and the functional neuroanatomical correlates corresponding to this conceptualization are presented. However, the first sentence containing the word "also" causes the expectation for continuum of a topic.

A4. Thank you for this comment. In the previous version, we used the word “also” to indicate that healthy older adults experience apathy as well, but this was not clear. We fixed the description as follows:

Page 4 Line 44

Apathy is observed in older adults with normal cognitive function and its prevalence is increased with aging and reduces their quality of life.

Q5. I think, the first paragraph of the Materials and Methods/Participants section also need to be reconsidered. Especially these two sentences are hard to follow: "335 people in the database were screened on the levels of apathy and the exclusion criteria. Exclusion criteria were: current or past presence of neurological or psychiatric disorders such as cerebrovascular disease, Mini-mental State Examination (MMSE) score less than 26 or dementia, diffuse or multiple cerebral white matter lesions on T2-weighted image, obvious cerebral atrophy, head motion > 2.0 mm during the scan of rs-fMRI". Since this section contains basic information for readers to understand the study, I think it would be more useful to give it in simpler sentences.

A5. Thank you for this advice. We have modified these sentences as follows:

Page 6 Line 86

A total of 335 people in the database were screened on their apathy levels and the exclusion criteria. Exclusion criteria were: current or past presence of neurological or psychiatric disorders; Mini-mental State Examination (MMSE) score less than 26 or dementia; obvious structural brain disorders; and head motion > 2.0 mm during the scan of rs-fMRI.

Q6. It is not common to use cut-off points on apathy scales. In general higher scores indicate higher levels of apathy. Was the cut-off point for the apathy scale used in a single study? Are there any other examples in recent studies, supporting the validation of this cut-off score other than the relevant reference (#32)?

A6. Thank you for this comment. Reference #28 was wrong. Okada et al. performed statistical validation of the cut-off point for the apathy scale. However, there are several studies that use this criterion (e.g., Yan et al.2015, Sugawara et al. 2011). The study by Yan et al. detected atrophy of the motor cortex in elderly individuals with apathy, while the study by Sugawara et al. indicated that hearing impairment was significantly associated with both MMSE and AS scores using the same criteria.

References

Yan H, Onoda K and Yamaguchi S (2015) Gray matter volume changes in the apathetic elderly. Front. Hum. Neurosci. 9:318. doi: 10.3389/fnhum.2015.00318

Norio Sugawara et al. Hearing impairment and cognitive function among a community-dwelling population in Japan. Annals of General Psychiatry 2011, 10:27

Q7. Explaining the scoring of depression scale will make it possible to understand the results and the table. Does this depression scale involves any cognitive tasks? If not, I would strongly recommend not to cluster depression scale under the neuropsychological assessment.

A7. Thank you for making this important point. The depression scale does not include cognitive tasks. Therefore, the heading of this paragraph has been revised as follows:

Page 7 Line 97

Neuropsychological and Neuropsychiatric measures

Q8. Line 151. Giving an analysis result and comparative reference information in the Method section may not be very appropriate. I recommend to relocate that sentence to Discussion.

A8. Thank you for this comment. The analysis the reviewer pointed out was simply conducted to confirm the reproducibility of our study. We moved this analysis result to a different section of the Results as follows:

Page 11 Line 173

The functional connectivity map of 6 striatal ROIs across 36 participants was similar to a previous study (Di Martino et al.) that demonstrated connectivity between striatum subdivisions and other cerebral regions such as the frontal cortex, parietal cortex, and temporal cortex.

Q9. Under the figure: A)… Red and blue foci indicate areas showing significant positive and negative connectivity.

It is better to clarify the color and connectivity direction.

A9. Thank you for this recommendation. We modified this as follows:

Page 13 Line 204

Red and blue foci indicate areas showing significant positive and negative connectivity differences, respectively.

Q10. Creating a table with peak Talairach coordinates for ROIs can make it easier for the readers to understand the results. It will also be convenient for the study to be repeated by other researchers.

A10. Thank you for this advice. We created a new Table 2 accordingly.

Page 12 Line 196

Q11. The authors drew attention to the overlap in symptoms of apathy and depression. However, if apathy and depression comorbidly present; it may not be easy to draw a line between these two syndrome as we can do between an internal disease and a psychiatric condition. It is known that both depression and apathy are the neuropsychiatric conditions that have independent effects on the molecular structure and physiological functioning of the brain. Statistically controlling the depression score may not result with subtracting the effect of depression from the brain activation as intended here in this study. I find the study's functional imaging analysis approach correct (controlling depression by adding the scores to analysis as covariant). However, adding multi covariates in fMRI analysis may suppress the overall activation which can cause underestimating the findings. In my opinion, in order to be able to say that the results were clearly independent of depression, a group of apathetic participants without depression should have been included. I would recommend the authors to discuss their method and findings stronger, in this context. Also, if the researchers have used any other tools or measurements, those can be included to manuscript in terms of increasing internal consistency.

A11. Thank you for providing these insights. Regarding the part of your comment which states “… to be able to say that the results were clearly independent of depression, a group of apathetic participants without depression should have been included.” , we tried to pick such individuals up from our database. However, we could not find elderly patients with high apathy and no depression due to their high comorbidity. Therefore, in this revised manuscript, we have added this as a limitation of our study. Please confirm that this is an acceptable change.

Page 17 Line 282

Moreover, to ensure that the participants were clearly independent of depression, an apathy group without depression should have been included.

Minor points:

Q1. Line 41. Mistyping of striatum as stratum

A1. As indicated, the spelling has been corrected.

Q2. Line 60. I would suggest using "study of cognitively normal aged people" instead of "study of cognitive- normal aged people"

A2. As indicated, the term has been corrected.

Q3. Line 85. I would suggest using "cranial MRI" instead of "head MRI"

A3. The suggested term has been used.

Q4. Line 104. This long sentence "Furthermore, all participants conducted the following neuropsychological assessments: Cognitive functions, assessed by the MMSE [29], the Frontal Assessment Battery (FAB) [30], and the Kohs Block Design Test (KOHS) [31]; depressive symptoms were evaluated using the Japanese version of Zung’s self-rating depression scale (SDS) [32]." can be simply expressed like "Furthermore, all participants conducted the following neuropsychological assessments: MMSE [29], Frontal Assessment Battery (FAB) [30], and Kohs Block Design Test (KOHS) [31]. Depressive symptoms were evaluated using the Japanese version of Zung’s self-rating depression scale (SDS)"

A4. Thank you for your comment. We modified this sentence as follows:

Page 7 Line 104

Furthermore, all participants conducted the following neuropsychological assessments: MMSE [29], Frontal Assessment Battery (FAB) [30], and Kohs Block Design Test (KOHS) [31]. Depressive symptoms were evaluated using the Japanese version of Zung’s self-rating depression scale (SDS) [32].

Q5. Line 126. Could the authors have meant "adjust" by using the phrase "to agree with" in this sentence: Next, the functional images were normalized to the standard space defined by a template T1-weighted image and resliced with a voxel size of 3x3x3 mm3 to agree with the gray matter probability maps.

A5. Thank you for your advice. We made modifications as follows:

Page 8 Line 123

Next, the functional images were normalized to the standard space defined by a template T1-weighted image and resliced with a voxel size of 3x3x3 mm3 to adjust the gray matter probability maps.

Q6. Line 209. If the intended meaning is not the process of aging; authors may consider using "elderly" instead of using the expression "aged people".

A6. The suggested expression has been used as follows:

Page 13 Line 214

Our results indicate that functional disruption of frontal-striatal circuits is associated with apathetic state in the elderly, independent of depression.

We look forward to hearing from you regarding our submission. We would be glad to respond to any further questions and comments that you may have.

Sincerely,

Chizuko Hamada, M.D.

Department of Neurology, Shimane University

89-1, Enyacho, Izumo, Shimane, Japan, 693-8501

E-mail: okuzihc@med.shimane-u.ac.jp

Submitted filename: Rebuttal_Letter.docx

Click here for additional data file.

11 Nov 2021

PONE-D-21-12168R1Altered resting-state functional connectivity of the frontal-striatal circuit in elderly with apathyPLOS ONE

Dear Dr. Hamada,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please address the comment of reviewer #1.

Please submit your revised manuscript by Dec 26 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

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Comments to the Author

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Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

**********

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The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Partly

**********

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Reviewer #1: Yes

Reviewer #2: Yes

**********

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Reviewer #1: Yes

Reviewer #2: No

**********

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Reviewer #2: Yes

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Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors have addressed most of my concerns well. However, in line 139, the bandpass filter COULD NOT be 0.08-0.09Hz, the typic one should be 0.01-0.09Hz. If this work was done with 0.08-0.09Hz, I do not think these is any signal left for functional connectivity calculation. Please Check.

Reviewer #2: Recommendations were found to be considered by the authors. According to my opinion, with the contributions of the editor and the other referee, this valuable study has become better presented. Since the significance intervals of the scores from the depression scale has not been explained, I think it is still not clear how pure is the patient group with apathy in the diagnostic sense. However, the authors were also showed sensitive approach to this point and took the recommendation into account by reporting this as a limitation. In this sense, there is nothing else I would like to point out. I hope that the authors will continue their work on this topic and replicate the results in further studies.

**********

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Reviewer #1: No

Reviewer #2: No

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29 Nov 2021

Journal requirements:（2021/11/12）

Q. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

A. We appreciate the helpful suggestion regarding Journal requirements. We fixed our reference list as follows:

Page 24 Line 399-400

2019; 101(1):165-177.e5. doi:10.1016/j.neuron.2018.11.016

Page 24 Line 409

doi:10.31887/DCNS.2016.18.1/shaber

Page 25 Line 414

doi:10.1523/JNEUROSCI.11-03-00667.1991

Page 25 Line 428

doi:10.1016/sS0006-8993(99)01531-0

Comments to the Author

6. Review Comments to the Author

Reviewer #1

Q. The authors have addressed most of my concerns well. However, in line 139, the bandpass filter COULD NOT be 0.08-0.09Hz, the typic one should be 0.01-0.09Hz. If this work was done with 0.08-0.09Hz, I do not think these is any signal left for functional connectivity calculation. Please Check.

A. Thank you for your comment. We have confirmed, and the bandpass filter was 0.008, not 0.08. We fixed the bandpass filter as follows:

Page 8 Line 130

band-pass filtering of 0.008–0.09 Hz.

We look forward to hearing from you regarding our submission. We would be glad to respond to any further questions and comments that you may have.

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

1 Dec 2021

Altered resting-state functional connectivity of the frontal-striatal circuit in elderly with apathy

PONE-D-21-12168R2

Dear Dr. Hamada,

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Additional Editor Comments (optional):

Reviewers' comments:

3 Dec 2021

PONE-D-21-12168R2

Altered resting-state functional connectivity of the frontal-striatal circuit in elderly with apathy

Dear Dr. Hamada:

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on behalf of

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Academic Editor

PLOS ONE