Kenichi Shibuya

Quantification of delayed oxygenation in ipsilateral primary motor cortex compared with contralateral side during a unimanual dominant-hand motor task using near-infrared spectroscopy

Using near-infrared spectroscopy (NIRS) techniques, it is possible to examine bilateral motor cortex oxygenation during a static motor task. Cortical activation was assumed to be reflected by increased oxygenation. The purpose of the present study was to examine the time course of oxygenation in the bilateral motor cortex during a low-intensity handgrip task. Six healthy, right-handed subjects participated in the study. The near-infrared spectroscopy probes positioned over the bilateral motor cortex were used to measure the cortical activation throughout a handgrip task carried out. The subjects performed a 3-min handgrip task with increasing intensity in a ramp-like manner [10-30% of the maximal voluntary contraction (MVC) at 6.67% MVC.min(-1)]. Contralateral motor cortex oxygenation increased significantly from 100 to 180 s after the start of the motor task compared with the baseline value (p<0.05). Ipsilateral motor cortex oxygenation also increased significantly from 130 to 180 s after the start of the motor task (p<0.05). The onset of increase in oxyhemoglobin ([HbO2]) and decrease in deoxyhemoglobin ([Hb]) in contralateral motor cortex area (M1) were significantly earlier than in ipsilateral M1 (respectively, p<0.05). These results show that there is a delayed oxygenation in ipsilateral primary motor cortex area compared with contralateral side during a unimanual dominant-hand motor task.

Human motor cortex oxygenation during exhaustive pinching task

There are few observations of the activity of the bilateral motor cortex during prolonged exhaustive motor tasks. Knowing how the motor cortex modulates muscle fatigue or how information about fatigue affects motor cortex activities in healthy humans may help explain why fatigue is so prevalent in patients with neurological disorders. The purpose of the present study was to investigate the time course of oxygenation of the bilateral motor cortex during an exhaustive pinching task. Eight healthy, right-handed subjects participated in the study. Near-infrared spectroscopy over the bilateral motor cortex was used to measure the activity throughout the pinching task. Subjects performed a sustained 50-60% of maximal voluntary contraction until voluntary exhaustion was reached. After the start of the motor task, the contralateral motor cortex oxygenation increased significantly compared with the resting value (P<0.05). However, with the passage of time, it decreased significantly compared with the resting value (P<0.05). In addition, ipsilateral motor cortex oxygenation decreased significantly at voluntary exhaustion compared with the resting value (P<0.05). These results suggest an interaction between the bilateral motor cortices during motor tasks.

Central command and the increase in middle cerebral artery blood flow velocity during static arm exercise in women

We examined the role of central command in static exercise‐induced increase in middle cerebral artery mean blood flow velocity (VMCA). Eleven young female subjects performed static elbow flexion for 2 min at 30% maximal voluntary contraction without (control exercise; CONT) and with vibrations to the biceps brachii tendon (EX+VIB) in order to reduce the effort needed to maintain the set contraction intensity. The rating of perceived exertion in exercising muscle (Arm RPE) at the end of EX+VIB was lower than that of CONT (mean ±s.d.; 4.8 ± 1.1 for CONT versus 3.5 ± 1.0 for EX+VIB; P < 0.05). The increases in mean arterial pressure (36 ± 8 versus 22 ± 7%; P < 0.05), heart rate (36 ± 16 versus 21 ± 7%; P < 0.05) and cardiac output (56 ± 26 versus 39 ± 14%; P < 0.05) during EX+VIB were also lower than those during CONT. Similarly, the increase in the VMCA during EX+VIB was lower than that during CONT (29 ± 5 versus 17 ± 14%; P < 0.05). These results suggest that the influence of central command contributes to cerebral blood flow regulation during static exercise and the decrease in VMCA is likely to be caused by attenuated brain activation in the central command network and/or by the reduction in cardiac output.

DECREASED ACTIVATION IN THE PRIMARY MOTOR CORTEX AREA DURING MIDDLE-INTENSITY HAND GRIP EXERCISE TO EXHAUSTION IN ATHLETE AND NONATHLETE PARTICIPANTS

It remains unclear whether activation kinetics in the motor cortex area is affected by training. The purpose of the present study was to examine the effect of training on the motor cortex activation. To accomplish this, the correlation between maximal voluntary contraction and motor cortex (M1) activity was examined. Differences in the motor cortex activation between two groups during exercise were examined in 14 male volunteer participants (M age 25.2 yr., SD = 1.4): seven highly trained athletes (VO2max = 60 ml/kg/min.; maximal voluntary contraction > 55 kg, M MVC = 63.6 kg, SD = 4.2) and seven nonathletes (VO2max < 45 ml/kg/min.; MVC < 50.0 kg, M MVC = 43.5 kg, SD = 5.2). Participants were familiarized with the study protocol, during which they performed a maximal voluntary static handgrip test. Specifically, M1 activation was measured by near-infrared spectroscopy throughout a handgrip exercise in which participants performed a sustained middle-intensity handgrip exercise (50% of maximal voluntary contraction) until voluntary exhaustion. In the Athlete group, activation in the M1 at voluntary exhaustion fell below the resting value. In the Nonathlete group, activation in the M1 was elevated throughout the exercise. Results suggest that motor signals from the motor cortex area correlate with exercise training status, especially during fatiguing exercise.

Satiety Relaxes Thinness Criteria When Judging Others’ Body Shapes

While people might endorse tolerance, social/environmental biases can remain operative and drive action in an unconscious manner. Herein, we investigated whether the criteria for judging others’ body shapes as “fat” or “thin” change with the degree of satiety. Nine females participated in the present study. The participants judged nine women’s figures as fat or skinny on a computer monitor in two conditions (Fasting and Satiety). Each figure ranged in body mass index (BMI) from 18.3 to 45.4 (i.e., 18.3, 19.3, 20.9, 23.1, 26.2, 29.9, 34.3, 38.6, and 45.4). Parameter estimates showed that a one-unit change in condition (Fasting vs. Satiety) resulted in a 20.0% greater probability of switching from “fat” to “thin” (SE = 0.056, z = 3.631, p < 0.0001). Notably, figures judged as “fat” in the fasting condition were judged as “thin” in the satiety condition. Thus, we concluded that satiety relaxes criteria for judging the thinness of others’ body shapes.

Relationship between the Influence of Others’ Opinions on Taste during Co-Eating and the Empathy of Individuals

The purpose of this study was to investigate whether the opinions of people eating together affect the taste of the foods they eat. In addition, if the opinions of others influence taste for one of the people eating with them, are the others’ opinions related to the empathy of individuals? Finally, this study was also intended to consider whether the taste threshold changes depending on the opinions of others. Twelve healthy young women (aged 18.4 ± 0.8 years; mean ± SD) participated in the present study. The participants tasted bread under three conditions: 1) quiet condition: a participant ate with three quiet persons, 2) positive condition: a participant ate with three persons who were talking favorably about taste, and 3) negative condition: a participant ate with three persons who were talking negatively about the taste. The electrical taste threshold was tested before and after tasting the bread, and a visual analog scale (VAS) was completed immediately after the tasting. Before the first trial, participants were asked to complete the Interpersonal Reactive Index (IRI). In the positive condition, the taste score increased significantly compared with the negative condition. There was no significant relationship between taste and empathic concern. To our knowledge, taste changed according to the comments of other people who were eating together. However, the change in taste due to the other’s speech was not related to the individual’s empathy. The results of the present study suggest that people experience food as delicious when others eating with them comment about the food being “delicious,” and this tendency did not depend on individuals’ empathy.

Effect of Gum Chewing Frequency on Oxygenation of the Prefrontal Cortex

Since increased cerebral oxygenation reflects cerebral activation, this study investigated the effect of mastication frequency on prefrontal cortex oxygenation. Eleven young volunteers (nine women, two men; M age = 20.9 years, SD = 0.9) carried out three trials in which they were asked to chew a tasteless gum for 3 min at varying (rates of mastication frequency: 30, 70, and 110). Breaks of 2 min each were interleaved between trials. The oxygenation of the left prefrontal cortex was monitored by near-infrared spectroscopy. We found a significant increase in cortical oxygenation during gum chewing in all three conditions (p < .05), compared with a resting level; we also found a significant difference between the Fast and Slow chewing conditions, and between the Fast and Normal (70 rpm) conditions, both findings seemingly related to activation of a motor command in frontal brain regions. To our knowledge, this is the first report on the effect of mastication frequency on cerebral oxygenation. Possible implications of this finding are discussed.

Central command and the increase in middle cerebral artery blood flow velocity during static arm exercise in women: Experimental Physiology

We examined the role of central command in static exercise‐induced increase in middle cerebral artery mean blood flow velocity (VMCA). Eleven young female subjects performed static elbow flexion for 2 min at 30% maximal voluntary contraction without (control exercise; CONT) and with vibrations to the biceps brachii tendon (EX+VIB) in order to reduce the effort needed to maintain the set contraction intensity. The rating of perceived exertion in exercising muscle (Arm RPE) at the end of EX+VIB was lower than that of CONT (mean ±s.d.; 4.8 ± 1.1 for CONT versus 3.5 ± 1.0 for EX+VIB; P < 0.05). The increases in mean arterial pressure (36 ± 8 versus 22 ± 7%; P < 0.05), heart rate (36 ± 16 versus 21 ± 7%; P < 0.05) and cardiac output (56 ± 26 versus 39 ± 14%; P < 0.05) during EX+VIB were also lower than those during CONT. Similarly, the increase in the VMCA during EX+VIB was lower than that during CONT (29 ± 5 versus 17 ± 14%; P < 0.05). These results suggest that the influence of central command contributes to cerebral blood flow regulation during static exercise and the decrease in VMCA is likely to be caused by attenuated brain activation in the central command network and/or by the reduction in cardiac output.

Central command and the increase in middle cerebral artery blood flow velocity during static arm exercise in women: Central command and cerebral blood flow

We examined the role of central command in static exercise‐induced increase in middle cerebral artery mean blood flow velocity (VMCA). Eleven young female subjects performed static elbow flexion for 2 min at 30% maximal voluntary contraction without (control exercise; CONT) and with vibrations to the biceps brachii tendon (EX+VIB) in order to reduce the effort needed to maintain the set contraction intensity. The rating of perceived exertion in exercising muscle (Arm RPE) at the end of EX+VIB was lower than that of CONT (mean ±s.d.; 4.8 ± 1.1 for CONT versus 3.5 ± 1.0 for EX+VIB; P < 0.05). The increases in mean arterial pressure (36 ± 8 versus 22 ± 7%; P < 0.05), heart rate (36 ± 16 versus 21 ± 7%; P < 0.05) and cardiac output (56 ± 26 versus 39 ± 14%; P < 0.05) during EX+VIB were also lower than those during CONT. Similarly, the increase in the VMCA during EX+VIB was lower than that during CONT (29 ± 5 versus 17 ± 14%; P < 0.05). These results suggest that the influence of central command contributes to cerebral blood flow regulation during static exercise and the decrease in VMCA is likely to be caused by attenuated brain activation in the central command network and/or by the reduction in cardiac output.