Change-Driven M100 Component in the Bilateral Secondary Somatosensory Cortex: A Magnetoencephalographic Study.

Our previous demonstration that the M100 somatosensory evoked magnetic field (SEF) has a similar temporal profile, dipole orientation and source location whether induced by activation (ON-M100) or deactivation (OFF-M100) of electrical stimulation suggests a common cortical system to detect sensory change. While we have not recorded such change-driven components earlier than M100 using electrical stimulation, clear M50 responses were reported using both ON and OFF mechanical stimulation (Onishi et al. in Clin Neurophysiol 121:588-593, 2010). To examine the significance of M50 and M100 in reflecting the detection of somatosensory changes, we recorded these waveforms in 12 healthy subjects (9 males and 3 females) by magnetoencephalography in response to mechanical stimulation from a piezoelectric actuator. Onset and offset (ON and OFF) stimuli were randomly presented with three preceding steady state (PSS) durations (0.5, 1.5 and 3 s) in one consecutive session. Results revealed that (i) onset and offset somatosensory events elicited clear M50 and M100 components; (ii) M50 and M100 components had distinct origins, with M50 localised to the contralateral primary somatosensory cortex (cS1) and M100 to the bilateral secondary somatosensory cortex (iS2, cS2); and (iii) the amplitude of M50 in cS1 was independent of the PSS durations, whereas that of M100 in S2 was dependent on the PSS durations for both ON and OFF events. These findings suggest that the M50 amplitude in cS1 reflects the number of activated mechanoreceptors during Onset and Offset, whereas the M100 amplitude in S2 reflects change detection based on sensory memory for Onset and Offset stimuli at least in part. We demonstrated that the M50 in cS1 and M100 in S2 plays different roles in the change detection system in somatosensory modality.

Effect of changes in stimulus site on activation of the posterior parietal cortex.

A previous functional magnetic resonance imaging study elucidated the specific activity of the inferior parietal lobe (IPL) during a two-point discrimination task compared with that during an intensity discrimination task Akatsuka et al. (Neuroimage 40: 852-858, 2008). If the posterior parietal cortex (PPC), including IPL, is responsible for detecting changes in stimulus sites, PPC activity depends on the level of change at stimulus sites. The aim of this study was to clarify whether a particular site exists that could detect changes in stimulus sites using the oddball paradigm. Somatosensory-evoked magnetic fields were recorded in 10 right-handed subjects. Three oddball conditions were performed by all subjects, with the probability of deviant and standard stimuli being 20 and 80 %, respectively, under all three conditions. Deviant stimuli were always presented to the second digit of the hand and standard stimuli were presented to the first (small deviance: SD) and fifth digits (medium deviance: MD) of the hand and the first digit of the toe (large deviance: LD). Inter-stimulus intervals were set at 500 ms. A brain electrical source analysis showed that activities of areas 1 and 3b elicited by the deviant stimuli were not significantly different among the three conditions. In contrast, PPC activity was significantly greater for LD than for SD and MD. PPC activity tended to increase with greater deviance at stimulus sites, but activities of areas 1 and 3b did not differ. These findings suggest that PPC may have a functional role in automatic change detection systems with regard to deviance of stimulus sites.

Skill-specific changes in somatosensory-evoked potentials and reaction times in baseball players.

Athletic training is known to induce neuroplastic alterations in specific somatosensory circuits, which are reflected by changes in short-latency somatosensory-evoked potentials (SEPs). The aim of this study is to clarify whether specific training in athletes affects the long-latency SEPs related to information processing of stimulation. The long-latency SEPs P100 and N140 were recorded at midline cortical electrode positions (Fz, Cz, and Pz) in response to stimulation of the index finger of the dominant hand in fifteen baseball players (baseball group) and in fifteen athletes in sports such as swimming, track and field events, and soccer (sports group) that do not require fine somatosensory discrimination or motor control of the hand. The long-latency SEPs were measured under a passive condition (no response required) and a reaction time (RT) condition in which subjects were instructed to rapidly push a button in response to stimulus presentation. The peak P100 and peak N140 latencies and RT were significantly shorter in the baseball group than the sports group. Moreover, there were significant positive correlations between RT and both the peak P100 and the peak N140 latencies. Specific athletic training regimens that involve the hand may induce neuroplastic alterations in the cortical hand representation areas playing a vital role in rapid sensory processing and initiation of motor responses.

Relationship between Step Characteristics and Race Performance during 5000-m Race.

This study examined the relationship between step characteristics and race time in a 5000-m race. Twenty-one male Japanese endurance runners performed a 5000-m race. Step length, step frequency, contact time, and flight time of two gait cycles (i.e., four consecutive ground contacts) were measured every 400-m by using high-speed video image. Moreover, step length was normalized to body height to minimize the effect of body size. In addition to step characteristics on each lap, the averages of all laps and the per cent change from the first half to the second half were calculated. The average step frequency and step length normalized to body height correlated significantly with the 5000-m race time (r = -0.611, r = -0.575, respectively, p < 0.05 for both). Per cent changes in contact time and step length correlated significantly with the 5000-m race time (r = 0.514, r = -0.486, respectively, p < 0.05 for both). These findings suggest that, in addition to higher step frequency and step length normalized to body height, smaller changes in step length during a given race may be an important step characteristic to achieving superior race performance in endurance runners.

Neuromuscular activation pattern of lower extremity muscles during pedaling in cyclists with single amputation of leg and with two legs: a case study.

OBJECTIVE: In Para-cycling competitions, cyclists with amputation of one-leg and no prosthesis, i.e., Division Cycle, Sport Class C2, perform pedaling movement on bicycle by unilateral leg. The purpose of this study was to describe neuromuscular activation of lower extremity muscles in two cyclists with single leg amputation and one cyclist with two legs during pedaling. We compared averaged rectified values (ARV) of surface electromyography for lower extremity muscles during crank cycle for two single leg cyclists with one cyclist with two legs at 65%, 80%, and 95% of VO2 max. RESULTS: Characteristic features of cyclists with single amputation of leg were increases in ARV for proximal region of the rectus femoris muscle in first half of pulling phase, increases in ARV for the biceps femoris muscle in first half of pulling phase, and increases in ARV for the medial gastrocnemius muscle in pulling phase. These findings in this study suggest that cyclists with single amputation of leg use characteristic neuromuscular coordination in the muscles contributing to hip and knee flexion joint moments during pulling phase and this may be the strategy in cyclists with single amputation of leg to compensate lack of hip and/or knee extension torque from contralateral leg.

Acute aerobic exercise influences the inhibitory process in the go/no-go task in humans.

This study evaluated the influence of acute aerobic exercise on the human inhibitory system. For studies on the neural mechanisms of somato-motor inhibitory processing in humans, the go/no-go task is a useful paradigm for recording event-related potentials. Ten subjects performed somatosensory go/no-go tasks in a control condition and exercise condition. In the control condition, the subjects performed the go/no-go task before and after 20 min of rest. In the exercise condition, the subjects performed the go/no-go task before and after 15 min of treadmill running with the exercise intensity set individually for each subject at 50% of peak oxygen intake. We successfully recorded a clear-cut N140 component under all conditions, and found that the peak amplitude of no-go-N140 at Fz and Cz was significantly enhanced during moderate exercise. In contrast, there were no significant changes in Fz and Cz in the control condition. These results suggest that moderate exercise can affect the amplitude of no-go-N140, which could be interpreted as an index of the human inhibition process in the central nervous system. The human inhibitory system is an important cognitive process, and this system may underlie the hypothetical ability of physical exercise to maintain and improve cognitive performance throughout the lifespan.

Skill-Specific Changes in Somatosensory Nogo Potentials in Baseball Players.

Athletic training is known to induce neuroplastic alterations in specific somatosensory circuits, which are reflected by changes in somatosensory evoked potentials and event-related potentials. The aim of this study was to clarify whether specific athletic training also affects somatosensory Nogo potentials related to the inhibition of movements. The Nogo potentials were recorded at nine cortical electrode positions (Fz, Cz, Pz, F3, F4, C3, C4, P3 and P4) in 12 baseball players (baseball group) and in 12 athletes in sports, such as track and field events and swimming, that do not require response inhibition, such as batting for training or performance (sports group). The Nogo potentials and Go/Nogo reaction times (Go/Nogo RTs) were measured under a somatosensory Go/Nogo paradigm in which subjects were instructed to rapidly push a button in response to stimulus presentation. The Nogo potentials were obtained by subtracting the Go trial from the Nogo trial. The peak Nogo-N2 was significantly shorter in the baseball group than that in the sports group. In addition, the amplitude of Nogo-N2 in the frontal area was significantly larger in the baseball group than that in the sports group. There was a significant positive correlation between the latency of Nogo-N2 and Go/Nogo RT. Moreover, there were significant correlations between the Go/Nogo RT and both the amplitude of Nogo-N2 and Nogo-P3 (i.e., amplitude of the Nogo-potentials increases with shorter RT). Specific athletic training regimens may induce neuroplastic alterations in sensorimotor inhibitory processes.

Whole-body water flow stimulation to the lower limbs modulates excitability of primary motor cortical regions innervating the hands: a transcranial magnetic stimulation study.

Whole-body water immersion (WI) has been reported to change sensorimotor integration. However, primary motor cortical excitability is not affected by low-intensity afferent input. Here we explored the effects of whole-body WI and water flow stimulation (WF) on corticospinal excitability and intracortical circuits. Eight healthy subjects participated in this study. We measured the amplitude of motor-evoked potentials (MEPs) produced by single transcranial magnetic stimulation (TMS) pulses and examined conditioned MEP amplitudes by paired-pulse TMS. We evaluated short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) using the paired-TMS technique before and after 15-min intervention periods. Two interventions used were whole-body WI with water flow to the lower limbs (whole-body WF) and whole-body WI without water flow to the lower limbs (whole-body WI). The experimental sequence included a baseline TMS assessment (T0), intervention for 15 min, a second TMS assessment immediately after intervention (T1), a 10 min resting period, a third TMS assessment (T2), a 10 min resting period, a fourth TMS assessment (T3), a 10 min resting period, and the final TMS assessment (T4). SICI and ICF were evaluated using a conditioning stimulus of 90% active motor threshold and a test stimulus adjusted to produce MEPs of approximately 1-1.2 mV, and were tested at intrastimulus intervals of 3 and 10 ms, respectively. Whole-body WF significantly increased MEP amplitude by single-pulse TMS and led to a decrease in SICI in the contralateral motor cortex at T1, T2 and T3. Whole-body WF also induced increased corticospinal excitability and decreased SICI. In contrast, whole-body WI did not change corticospinal excitability or intracortical circuits.