Biomedical subjects

Tomohiro Kizuka

Publications and source records attributed to Tomohiro Kizuka.

10 recordsLinked to original sources

PubMed2006

A comparison of stimulus synchronous activity in the primary motor cortices of athletes and non-athletes.

In this study, we measured primary motor cortex (MI) activity during a reaction time task to examine the appearance of MI activity that synchronized with the stimulus presentation (stimulus synchronous MI activity, SSMA). Because brain activity was expected to be enhanced by the repetitive/extensive activation, we hypothesized that the SSMA would be more clearly observable in athletes who were trained to perform reactive movements than in non-athletes. MI activity was measured in ten athletes and ten non-athletes by magnetoencephalography. The tasks were a simple reaction task and a Go/Nogo reaction task in which the subjects were asked to abduct their right index fingers in response to a visual stimulus. The Go/Nogo reaction time task was adopted to confirm the presence of the SSMA, because the MI activity in response to a Nogo stimulus did not overlap with the MI activity that was synchronous with the execution of the movement. The results show that the SSMA was clearly apparent in the athlete group (9/10). In the non-athlete group, however, only three subjects showed the SSMA (3/10). Moreover, the MI activity of the athletes tended to be larger than that of the non-athletes, even though the athletes did not specifically practice these index finger movements during their daily training. We concluded that long-term physical training promotes MI activity and the effects of reactive task repetition were more clearly apparent in the MI activity of the athletes.

Adult↗

PubMed2006

Reduction in maximal firing rate of motoneurons after 1-week immobilization of finger muscle in human subjects.

We investigated the effects of immobilization on the maximal motoneuronal firing rate recorded from the first dorsal interosseous (FDI) during voluntary isometric contraction. In five human subjects, the middle finger, index finger, and thumb were immobilized for 1 week in a fiber-glass cast, which kept FDI in a shortened position. During a maximal voluntary contraction, single muscle-fiber action potentials were recorded using a tungsten microelectrode, and mean firing rate was calculated for each action-potential train. Three recording sessions were held: before immobilization (pre), after immobilization (post), and after a 1-week recovery period (recovery). The mean firing rate of FDI motoneurons during maximal voluntary contraction was decreased immediately after the 1-week immobilization (pre: 39.0+/-3.2 Hz, number of detected spike trains (n)=353; post: 33.1+/-1.5 Hz, n=285; p<0.05), and there was a return to control after the recovery period (40.2+/-3.4 Hz, n=236). This suggests that the maximal motoneuronal firing rate achieved during maximal voluntary contraction is reduced after short-term immobilization. The functional implications and the contribution of this phenomenon to the immobilization-induced reduction in maximal voluntary force are discussed.

Action Potentials↗

PubMed2005

Increased c-fos gene expression in alpha motoneurons in rat loaded hindlimb muscles with inclined locomotion.

The potential usefulness of c-fos gene expression as an indicator of the activity level of spinal alpha motoneurons was examined in loaded locomotive rats. The motor pools of the plantaris (PL) and soleus muscles (SOL), mainly composed respectively of fast- and slow-twitch muscle fibers, were investigated in rats under locomotion at 25 m/min on a 20% incline. We first labeled motoneurons with a retrograde tracer, Nuclear Yellow (NY), and then quantified the c-fos mRNA expression level in the NY-labeled alpha motoneurons by means of in situ hybridization. Electromyographic (EMG) activities were also recorded. The c-fos expression level per alpha motoneuron showed a greater increase in the PL (75%) than in the SOL motor pool (38%). EMG activities also showed a greater increase in the PL (159%) than in the SOL (43%). Taken together, these results suggest that c-fos expression levels in alpha motoneurons are associated with the activity levels of their corresponding muscle. This cytochemical method for identifying the c-fos expression level has potential for use as a tool for estimating the activity level of large populations of alpha motoneurons in unrestricted animals.

Animals↗

PubMed2005

Automatic and imperative motor activations in stimulus-response compatibility: magnetoencephalographic analysis of upper and lower limbs.

The stimulus-response (S-R) compatibility effect refers to the difference in performance due to the spatial S-R relationship in choice reaction time. We investigated the mechanism of neural activities in S-R compatibility at the level of the primary motor cortices for upper and lower limbs responses using magnetoencephalography (MEG). In the S-R compatible task, subjects were required to respond on the same side of the stimulus light using either an upper or lower limb. In the incompatible task, subjects were required to respond in the reverse manner. Premotor times of upper and lower limbs were faster for the compatible response than for the incompatible response. The neuromagnetic brain activities related to response execution were estimated using a multi-dipole model. Stimulus-locked MEG indicated that the current moments of motor dipoles for both effectors occurred bilaterally and reached the first peak at a constant delay irrespective of whether the task was compatible or incompatible. This indicates that the neural activation of the primary motor cortex is automatically synchronized with the stimulus onset. Response-locked MEG showed that the peak current moment of the motor dipole contralateral to the response was stronger for the compatible task than for the incompatible one regardless of whether the responses were made using the upper or lower limbs. The MEG results suggest that automatic motor activation facilitates imperative motor activation for a compatible response, whereas it is not sufficient to prime imperative motor activation for an incompatible response.

Adult↗

PubMed2005

Stimulus-response compatibility and response preparation: effects on motor component of information processing for upper and lower limb responses.

The effects of stimulus-response compatibility and response preparation on the motor component of the information processing system were investigated by analyzing the fractionated reaction time for the upper and lower limbs. The reaction time was divided into two periods with respect to the onset of electromyographic activity, premotor and motor times. The response preparation was manipulated by the probability that the locations of the precue and subsequent imperative stimulus corresponded. On a stimulus-response compatible task, subjects were required to release a key on the same side as an imperative stimulus, irrespective of the precued side. On an incompatible task, subjects were required to act in the reverse manner. The upper and lower limb responses were measured during both tasks. A repeated-measures design was used with 12 male university students. Analysis of the reaction and premotor times indicated that the stimulus-response compatibility effect became larger as response preparation decreased. The analysis of motor time yielded significant interactions between stimulus-response compatibility and limb and between response preparation and limb. These findings indicated that the motor component of information processing for the lower limb response is affected by both stimulus-response compatibility and response preparation.

Adolescent↗

PubMed2005

The impact of metabolic stress on hormonal responses and muscular adaptations.

PURPOSE: The purpose of this study was to examine the impact of exercise-induced metabolic stress on hormonal responses and chronic muscular adaptations. METHODS: We compared the acute and long-term effects of an "NR regimen" (no-rest regimen) and those of a "WR regimen" (regimen with rest period within a set). Twenty-six male subjects were assigned to either the NR (N = 9), WR (N = 9), or control (CON, N = 8) groups. The NR regimen consisted of 3-5 sets of 10 repetitions at 10-repetition maximum (RM) with an interset rest period of 1 min (lat pulldown, shoulder press, and bilateral knee extension). In the WR regimen, subjects completed the same protocol as the NR regimen, but took a 30-s rest period at the midpoint of each set of exercises in order to reduce exercise-induced metabolic stress. Acute hormonal responses to both regimens were measured followed by a 12-wk period of resistance training. RESULTS: Measurements of blood lactate and serum hormone concentrations after the NR and WR regimens showed that the NR regimen induced strong lactate, growth hormone (GH), epinephrine (E), and norepinephrine (NE) responses, whereas the WR regimen did not. Both regimens failed to cause significant changes in testosterone. After 12 wk of resistance training, the NR regimen caused greater increases in 1RM (P < 0.01), maximal isometric strength (P < 0.05), and muscular endurance (P < 0.05) with knee extension than the WR regimen. The NR group showed a marked increase (P < 0.01) in muscle cross-sectional area, whereas the WR and CON groups did not. CONCLUSION: These results suggest that exercise-induced metabolic stress is associated with acute GH, E, and NE responses and chronic muscular adaptations following resistance training.

Adult↗

PubMed2004

Bilateral cerebral activity for unilateral foot movement revealed by whole-head magnetoencephalography.

The primary motor cortices controlling foot movement are located on opposite sides of the longitudinal fissure. As a separation of closely located activity sources is not successful, the possibility of bilateral activation for lower limb movement remains undetermined. We therefore examined cerebral activity during unilateral foot movement to investigate the possibility of bilateral activation of primary foot motor cortices. Self-paced foot movement and finger movement (for comparison) were performed on ten subjects. Brain magnetic fields were recorded using a 64-channel whole-cortex magnetoencephalography (MEG) system. Brain activities were identified using 1- to 3-dipole models. Results evaluating finger movement were similar to previous reports. Equivalent current dipoles (ECDs) for foot movements were estimated in the primary foot motor and sensory regions. Sensory activity was always localized to the contralateral hemisphere. Motor activity was estimated by one ECD, but the laterality differed between subjects. Additional activity was discovered together with the primary motor activity, localized around the precentral sulcus. In contrast to consistent results of primary sensory activity, the variation of laterality of the foot primary motor ECD can be explained with a cancellation model, in which the magnetic fields generated from two closely spaced ECDs overlap to cancel each other out. Consequently, activation of the primary foot motor cortices was determined to be bilateral. Furthermore, it was estimated that additional activity may occur in the premotor area. This work suggests not only the bilateral activation of the primary foot motor cortices but also the possibility of a contribution of the premotor area.

Adult↗

PubMed2004

Reductions in basal limb blood flow and lumen diameter after short-term leg casting.

PURPOSE: We tested the hypotheses that short-term casting immobilization of a leg would reduce basal blood flow and vascular conductance and induces structural alterations in femoral artery. METHODS: Right knee and ankle joints of eight healthy young men were immobilized with casting for 7 d. Before and immediately after casting, and 14 d after the cast was removed, femoral artery hemodynamics and structure were measured using a high-resolution ultrasound. RESULTS: Femoral artery lumen diameter in the immobilized leg decreased after the immobilization (P < 0.05) and returned to baseline during the recovery period, in which the subjects did not receive any special rehabilitation treatment. Femoral artery intima-media thickness (IMT) and IMT/lumen ratio in both legs did not show significant changes throughout the interventions. In the immobilized leg, femoral artery blood flow and vascular conductance decreased (-23 to 24%) after the immobilization (all P < 0.05). These parameters returned to the baseline during the recovery period, and there were no significant differences between the baseline and recovery values. In the control leg, femoral blood flow and vascular conductance did not change throughout the investigation. After 7 d of casting, femoral arterial distension, an index of arterial distensibility, tended to decrease in the immobilized leg but not in the control leg. CONCLUSION: We concluded that a short-term immobilization of lower limb decreases basal limb blood flow and arterial lumen diameter. These results suggest that basal limb blood flow and lumen diameter decrease rapidly upon the cessation of muscular weight bearing and locomotor activity, and may be modulated by an ordinary level of physical activity.

Adult↗

PubMed2004

Muscular adaptations to combinations of high- and low-intensity resistance exercises.

Acute and long-term effects of resistance-training regimens with varied combinations of high- and low-intensity exercises were studied. Acute changes in the serum growth hormone (GH) concentration were initially measured after 3 types of regimens for knee extension exercise: a medium intensity (approximately 10 repetition maximum [RM]) short interset rest period (30 s) with progressively decreasing load ("hypertrophy type"); 5 sets of a high-intensity (90% of 1RM) and low-repetition exercise ("strength type"); and a single set of low-intensity and high-repetition exercise added immediately after the strength-type regimen ("combi-type"). Postexercise increases in serum GH concentration showed a significant regimen dependence: hypertrophy-type > combi-type > strength-type (p < 0.05, n = 8). Next, the long-term effects of periodized training protocols with the above regimens on muscular function were investigated. Male subjects (n = 16) were assigned to either hypertrophy/combi (HC) or hypertrophy/ strength (HS) groups and performed leg press and extension exercises twice a week for 10 weeks. During the first 6 weeks, both groups used the hypertrophy-type regimen to gain muscular size. During the subsequent 4 weeks, HC and HS groups performed combi-type and strength-type regimens, respectively. Muscular strength, endurance, and cross sectional area (CSA) were examined after 2, 6, and 10 weeks. After the initial 6 weeks, no significant difference was seen in the percentage changes of all variables between the groups. After the subsequent 4 weeks, however, 1RM of leg press, maximal isokinetic strength, and muscular endurance of leg extension showed significantly (p < 0.05) larger increases in the HC group than in the HS group. In addition, increases in CSA after this period also tended to be larger in the HC group than in the HS group (p = 0.08). The results suggest that a combination of high- and low-intensity regimens is effective for optimizing the strength adaptation of muscle in a periodized training program.

Adaptation, Physiological↗

PubMed2004

Response preparation and stimulus-response congruence to fractionating reaction time of upper and lower limbs.

We measured the fractionating reaction time for upper and lower limbs of 18 young men, using an electromyogram to clarify the interaction of response preparation and stimulus-response congruence on premotor and motor time. The reaction time was divided into two periods with respect to the onset of the electromyogram, premotor and motor components. Manipulating the probability of the Go versus NoGo signals varied three different amounts of response preparation. Prior to the imperative stimulus, precue information about the position of a stimulus was presented. In the stimulus-response congruent task, subjects were required to release a key on the same side of the body using either an upper or lower limb in response to an imperative Go stimulus. In the stimulus-response incongruent task, subjects were required to act in a reverse manner. Subjects were not supposed to respond to the NoGo stimulus. The premotor time of the upper and lower limb responses was affected by the respective effects of response preparation and stimulus-response congruence. The motor time of the upper and lower limb responses increased as the probability of the Go signal decreased but not in relation to stimulus-response congruence. These results suggest that response preparation affects not only information processing time but also peripheral motor activity due to motor programming, and that the stimulus-response congruence effect on motor time disappears when information about the position of the imperative stimulus is precued.

Adolescent↗