Increased thalamocortical connectivity from the affected thalamus to the unaffected hemisphere in a stroke patient.

Consciousness is controlled by complicated actions of various neural structures (Schiff, 2010; Long et al., 2016). The thalamocortical connections between the central thalamus and cerebral cortex are considered an important neural structure for consciousness (Laureys et al., 2000; Schiff, 2010; Jang and Lee, 2015). Here, we report a patient who revealed increased thalamocortical connectivity from the affected thalamus to the unaffected hemisphere through interthalamic adhesion.

A 79-year-old right-handed female underwent decompressive craniectomy for brain swelling due to infarction in the right intracerebral artery territory. At 10 weeks after onset when she started rehabilitation, brain MRI showed a leukomalatic lesion in the right fronto-parieto-occipito-temporal lobes, subcortical white mater, and midbrain (). The patient showed a vegetative state, with a Glasgow Coma Scale score of 6 (eye opening: 1, best verbal response: 1, and best motor response: 4) (full score: 15), Coma Recovery Scale-Revised score of 3 (auditory: 0, visual: 0, motor: 2, verbal: 1, communication: 0, and arousal: 0) (full score: 23), Mini-Mental State Examination score of non-checkable (full score: 30), Functional Ambulation Category score of 0 (full score: 5) and Motricity Index score of 21 (right extremities), and 14 (left extremities) (full score: 100) (Teasdale and Jennett, 1974; Folstein et al., 1975; Demeurisse et al., 1980; Cunha et al., 2002; Giacino et al., 2004). The patient provided signed informed consent. This study was conducted retrospectively, and approval for the study was obtained from the Institutional Review Board of Yeungnam University Hospital (approval No. YUMC-2019-06-032) on June 21, 2019.

DTT and MRI for a 79-year-old female patient with infarction in the right intracerebral artery territory.

(A) Brain magnetic resonance imaging at 10 weeks after onset showing leukomalatic lesion (red arrows) in the right fronto-parieto-occipito-temporal lobes, subcortical white matter, and midbrain. (B) Results of DTT for the ascending reticular activating system of the patient. On 10-week DTT, the right lower dorsal ascending reticular activating system reveals narrowing and the majority of the right thalamocortical connections are connected to the left hemisphere via the interthalamic adhesion compared with a normal subject (a 78-year-old female). A: Anterior; DTT: diffusion tensor tractography; MRI: magnetic resonance imaging; R: right.

Diffusion tensor imaging was obtained at 10 weeks after onset using a 6-channel head coil on a 1.5 T Philips Gyroscan Intera. Fiber tracking was conducted using Functional Magnetic Resonance Imaging of the Brain Diffusion Software with routine options (0.5 mm step lengths, 5000 streamline samples, curvature thresholds: 0.2). Two parts of the ascending reticular activating system (ARAS) were analyzed by the following regions of interest (ROI): the lower dorsal ARAS between the reticular formation of the pons (RF, seed ROI) and the intralaminar nuclei of the thalamus (ILN, target ROI) (Yeo et al., 2013), after which the thalamocortical connections between the ILN [seed ROI] and the cerebral cortex were reconstructed (Jang et al., 2014).

The right lower dorsal ARAS showed narrowing and the majority of the right thalamocortical connections were connected to the left hemisphere via the interthalamic adhesion ().

In this patient, DTT revealed that the majority of the thalamocortical connections between the ILN and the cerebral cortex in the right (affected) hemisphere were connected from the right thalamus to the left (unaffected) hemisphere through the interthalamic adhesion in a stroke patient. The central thalamus is a core structure of consciousness because it directly links to the cerebral cortex, brainstem and basal forebrain, and indirectly links to the cortico-basal ganglia-thalamo-cortical loop system (Schiff, 2010). It appears that the increased thalamocortical connections from the thalamic ILN of the affected hemisphere to the unaffected hemisphere in this patient might be a compensatory phenomenon to the severe damage of the affected hemisphere. A thalamus is connected to an opposite thalamus through the interthalamic adhesion. Many studies using DTT have demonstrated the thalamocortical connections between the ILN and the cerebral cortex in normal subjects and patients with recovery of injured thalamocortical connections following brain injury (Jang et al., 2014; Jang and Kwon, 2019). However, the phenomenon that the thalamocortical connections from the thalamic ILN to the opposite hemisphere has not been clarified in patients with disorders of consciousness as well as normal subjects (Jang et al., 2014; Jang and Kwon, 2019). Therefore, further studies on the anatomy and function of the thalamocortical connections from the thalamic ILN to the opposite hemisphere in both normal and pathologic conditions should be warranted.