Effects of blood flow to the prefrontal cortex on high-intensity exercise combined with high-decibel music.

We studied the effects of high-intensity exercise (70-75% of VO2 max) combined with high-decibel music (100 dB) on cognitive function (measured by the Stroop test) and related blood flow changes to the prefrontal cortex (measured by Oxy-hemoglobin (Hb), Deoxy-Hb, tissue oxygen index (TOI), and normalized tissue hemoglobin index (nTHI)). The subjects of the study were 28 healthy female university students in their early 20s. Subjects were categorized into control group (CG), music group (MG), exercise group (Ex), and music and exercise group (MnEx). A crossover design was implemented so that all subjects participated in all test groups. We found no significant difference in reaction time between CG and MG for the neutral and incongruent tasks of Stroop test. However, there were significant improvements in the neutral and incongruent tasks for both the Ex (p < 0.01) and MnEx (p < 0.01) groups. Oxy-Hb measurements in the prefrontal cortex of the brain supported the Stroop test data. We found no difference between Ex and MnEx in the TOI; however, there was a significant decrease (p < 0.05) in MnEx compared to Ex. In addition, Ex resulted in a significant increase (p < 0.05) in nTHI as compared to CG. These results indicate that high decibel music could negatively affect prefrontal cortex activation of the brain during exercise.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

In the field of music therapy, lyrical music with a stable beat and volume is generally used for psychotherapy because it induces mentally positive effects [1,2]. In contrast, High-Intensive Sound (HIS) including music could be recognized as a noise by some individuals. Music in general is played around 85 dB, rock bands with loud sounds play around 110 dB, and a jet engine's noise is around 150 dB. HIS of 120 dB or higher can cause a painful listening experience, and hearing impairment occurs if one is exposed continuously to a noise of 80 dB or higher. It has been reported that the sound of 96-110 dB can cause various negative effects on the body depending on the duration of the exposure [3]. As such, sound can affect the body either positively or negatively based on the volume.

High-decibel music (HDM) can be interpreted as noisy or joyful based on one's tolerance. The hedonic qualities of HDM are difficult to measure as they are subjective. HDM played during sports or exercise induces excitement, and it is occasionally used to maintain performance. However, despite countless research reports on brain activation by exercise, there have been hardly any studies on cognitive functions and brain activity stimulated by exercise combined with HDM.

Studies on the relationship between exercise and the brain have been actively pursued globally since 2000. Several research groups in Korea have demonstrated neurogenesis in the hippocampus and improved short-term memory in rodents in response to exercise [4-7]. Few studies in humans have assayed improvements in cognitive functions due to exercise. These studies have used the Stroop test [8] and the cerebral blood flow velocity [9-11]; however, none have looked at the activation of the brain and changes in oxygenated hemoglobin (Oxy-Hb). Various molecular biology and behavior studies have been conducted that found learning and memory increases in response to augmented neurogenesis in the hippocampus and a decreased time to find the platform in the Morris water maze task [12]. In humans, long-term medium intensity exercise resulted in memory improvements combined with decreased selection-reaction time, increased brain size, prefrontal cortex activation, and the improvements in cognitive function [13-15]. While studying the relationship between exercise and cerebral blood oxygenation using near infrared spectroscopy (NIRS), it has been observed that acute exercise increases Oxy-Hb of the prefrontal cortex, and that young people and the old people have different areas of brain activation during exercise [16,17]. Many aspects regarding the relation between brain activation and an age group, exercise intensity, exercise type, or surrounding environment remain to be explored.

NIRS, a method for assessing brain activation, is a non-invasive measurement that can monitor metabolic function by assessing blood flow and oxygen saturation using light wavelengths between 700-3,000 nm. NIRS can measure information about activation in a particular brain area by measuring the concentration changes in Oxy-Hb and deoxygenated hemoglobin (Deoxy-Hb) within the body (the brain or muscle). The biggest strength of NIRS, compared to other brain imaging methods, is that real-time assessment of exercise is possible as long as there are no drastic movements of the head such as in cycling. When performing a cognitive activity or exercise, neurons in the corresponding brain areas are activated, and they require oxygen supply for energy consumption. Blood flow increases to activated neurons to meet the demand. On such occasions, Oxy-Hb within the blood releases oxygen to neurons and is converted into Deoxy-Hb. To avoid a state of oxygen depletion due to oxygen consumption, an increase in Oxy-Hb concentration and decrease in Deoxy-Hb concentration occurs. The Stroop test is commonly used to measure prefrontal cortex activation. NIRS has been used to confirm that the Stroop test measures prefrontal cortex activation by detecting significant augmentation in Oxy-Hb in bilateral dorsolateral prefrontal cortex (DLPFC) during the task [16]. The prefrontal cortex is involved in thought, behavioral control, speech, decision making, emotional control, memory control, concentration, distraction, and motivation. Humans recognize the meaning of a letter subconsciously, and thus it is difficult to determine the letter and its color at the same time. This is called cognitive interference (Stroop interference), and it reflects the selection function of the prefrontal cortex [18-20]. Studies measuring cerebral blood flow during the Stroop task have demonstrated that patients with vascular dementia display poor performance on the Stroop task compared to healthy people because of reduced blood flow to the DLPFC area [21-23]. As the Stroop task requires prefrontal cortex activation, this simple test can infer the activation of brain function in the prefrontal cortex.

Several studies have reported that medium-intensity exercise increases the activation of the frontal lobe. However, people who exercise for health, including athletes, often perform high-intensity exercise combined with HDM to induce “excitement and fun.” Nevertheless, there have been few studies on the effects of listening to HDM during high-intensity exercise on cerebral activation.

Therefore, we studied blood flow changes to the prefrontal cortex using the Stroop test and NIRS in order to understand the effects of a combination of HDM and high-intensity exercise on the prefrontal cortex. This study seeks to explore the effects of being exposed to HDM during exercise on cognitive function.

METHODS

Subjects

The subjects of this study were 28 female university students. The study subjects did not have any particular disease and they were drug-free, healthy individuals, and such selection was done so that they can handle exercise stress of cycle ergometer without difficulties. They were categorized into 4 groups, Control Group (CG), Music Group (MG), Exercise Group (Ex), Music and Exercise Group (MnEx), and the study was conducted with a crossover design so that all the subjects were able to participate in all the 4 groups. All the subjects had a total of 5 tests including a maximal exercise stress test. The characteristics of subjects are listed in Table 1.

Table 1.

Characteristics of subjects (n=28)

	Age (years)	Height (cm)	Body Weight (kg)	% Body Fat (%)
Aver. ± SD.	21.1 ± 1.5	164.1 ± 3.7	56.8 ± 7.9	25.5 ± 4.6

Values are means ± SD

Maximal Oxygen Uptake Test

Maximal oxygen uptake was assessed with a gas analyzer in order to set equal exercise intensity relative to each subject's capacity (MediGraphic, VO2000, The U.S.). Regarding an assessment method protocol, warm up of 1 minute was done using cycle ergometer (Ergomedic 839E, Monark co., Sweden) and then started at 30W and increased 25W per every 2 minutes (Fig. 1). VO2 max and heart rate values from this test were used to set exercise stress.

Fig. 1.

The graded protocol of maximal oxygen uptake test using cycle ergometer

Stroop and NIRS test (Cognitive function)

We attached the sensor of NIRS equipment (Hamamatsu, NIRO-200) onto the prefrontal cortex area of the test subject, and had the subject sit on cycle ergometer and let her rest until the heart rate was stabilized on a wireless heart rate monitor. After the rest, 5 minutes of Stroop test was conducted with computer program. For a Stroop test method, 5 seconds was set for one question, and the time required to answered the question was assessed per millisecond. For a question method, it was processed alternatively with 1~10 being neutral, 11~20 being incongruent, 21~30 being neutral, 31~40 being incongruent, 41~50 being neutral and 51~60 being incongruent. 5 examples were given per question and the reaction time of pushing a computer key was assessed. Questions were comprised differently based on the test order of researchers per each session (Fig. 2).

Fig. 2.

Test design. Divided into a total of 4 groups and Stroop test was done before and after the intervention of 10 minutes. Neutral and incongruent tasks were given alternately per 50 seconds interval for a total of 5 minutes.

Experimental Procedure

All the stages of experiment were conducted as follows. 1) Analyzing height, weight and body fat (Inbody 7.0, Biospace) and getting consent for the experiment. 2) Having the subject sit on cycle ergometer, attaching NIRS sensor onto the prefrontal cortex area (left forehead) and putting on a wireless heart rate monitor. 3) After taking a rest, conducting 5 minutes of pre-Stroop test using computer program. 4) Conducting intervention for 10 minutes (CG: rest, MG: listening to the music of 100dB or higher, Ex: cycle exercise with 70-75% of VO2 max, MnEx: MG+Ex) → post-Stroop test. 5) During the entire process, Oxy-Hb, Deoxy-Hb, Tissue Oxygen Index (TOI: showing oxygen saturation) and normalized Tissue Hemoglobin Index (nTHI: indicator of hemoglobin to tissue) were assessed in real time with NIRS sensor, attached onto the prefrontal cortex.

Statistical analysis

All the result of this study was listed in Mean ± SD and IBM Statistics 20 was used for all the statistical analysis of this study. One-way ANOVA was conducted to understand differences based on each treatment, and post hoc test was conducted with Fisher’s LSD (Least Significant Difference) for the variables which showed a significant difference. For independent measurement variables, paired t-test was conducted to verify them. The significance level of 0.05 was used for all test.

RESULTS

The results obtained with maximal exercise stress test, using cycle ergometer, are listed in . For the test subjects, it took 8 minutes and 34 seconds from maximal exercise stress test to All-Out. Average maximum heart rate was 171.8 ± 15.4 times/minute and maximal oxygen uptake was 29.2 ± 4.3 ml/kg/min.