Differences in the recruitment properties of the corticospinal pathway between the biceps femoris and rectus femoris muscles.

The neuromuscular activity in the hamstring and quadriceps muscles is vital for rapid force control during athletic movements. This study aimed to investigate the recruitment properties of the corticospinal pathway of the biceps femoris long head (BFlh) and rectus femoris (RF) muscles. Thirty-two male subjects were participated in this study. Corticospinal excitability was investigated for BFlh and RF during the isometric knee flexion and extension tasks, respectively, using transcranial magnetic stimulation. A sigmoidal relationship was observed between the stimulus intensity and amplitude of motor-evoked potentials and characterized by a plateau value, maximum slope, and threshold. Compared with RF, BFlh had a significantly lower plateau value (P < 0.001, d = 1.17), maximum slope (P < 0.001, r = 0.79), and threshold (P = 0.003, d = 0.62). The results showed that the recruitment properties of the corticospinal pathway significantly differ between BFlh and RF. These results reveal that when a sudden large force is required during athletic movements, the RF can produce force through a rapid increase in the recruitment of motor units. The BFlh, on the other hand, requires larger or more synchronized motor commands for enabling the proper motor unit behavior to exert large forces. These differences in the neurophysiological factors between the hamstrings and quadriceps can have a substantial effect on the balance of force generation during athletic activities.

Effect of Long-Term Classical Ballet Dance Training on Postactivation Depression of the Soleus Hoffmann-Reflex.

Classical ballet dancing is a good model for studying the long-term activity-dependent plasticity of the central nervous system in humans, as it requires unique ankle movements to maintain ballet postures. The purpose of this study was to investigate whether postactivation depression is changed through long-term specific motor training. Eight ballet dancers and eight sedentary subjects participated in this study. The soleus Hoffmann reflexes were elicited at after the completion of a slow, passive dorsiflexion of the ankle. The results demonstrated that the depression of the soleus Hoffmann reflex (i.e., postactivation depression) was larger in classical ballet dancers than in sedentary subjects at two poststretch intervals. This suggests that the plastic change through long-term specific motor training is also expressed in postactivation depression of the soleus Hoffmann reflex. Increased postactivation depression would strengthen the supraspinal control of the plantarflexors and may contribute to fine ankle movements in classical ballet dancers.

Acquisition of novel ball-related skills associated with sports experience.

Some individuals can quickly acquire novel motor skills, while others take longer. This study aimed to investigate the relationships between neurophysiological state, sports experience, and novel ball-related skill acquisition. We enrolled 28 healthy collegiate participants. The participants' neurophysiological data (input-output curve of the corticospinal tract) were recorded through transcranial magnetic stimulation. Subsequently, the participants performed a novel motor task (unilateral two-ball juggling) on a different day, after which they reported their previous sports experience (types and years). We found that individuals with more years of experience in ball sports showed faster acquisition of novel ball-related skills. Further, this result was not limited to any single ball sport. Therefore, the acquisition of novel ball-related skills is associated with familiarity with a ball's nature. Furthermore, gain of the corticospinal tract was negatively and positively correlated with the years of experience in primary ball and non-ball sports (implemented for the longest time in individuals), respectively. These results could be associated with the extent of proficiency in their primary sport. The chosen type of sports (e.g., ball or non-ball) could critically influence the future acquisition of novel motor skills. This study provides important insights regarding how to approach sports and physical activities.

Acquisition and maintenance of motor memory through specific motor practice over the long term as revealed by stretch reflex responses in older ballet dancers.

The present study addressed whether motor memory acquired earlier in life through specific training can be maintained through later life with further training. To this end, the present study focused on the training effect of a specific ballet practice and investigated the spinally mediated stretch reflex responses of the soleus muscle in ballet dancers of upper-middle to old age (60.6 ± 5.4 years old) with experience levels of 28.4 ± 7.4 years ("older ballet" group). Comparisons were conducted with a group of young ballet dancers ("young ballet" group) and groups of both young and older individuals without weekly participation in physical activities ("young sedentary" and "older sedentary" groups). The results revealed natural age-dependent changes, with reflex responses being larger in older sedentary than in young sedentary individuals. A training-induced effect was also observed, with responses being smaller in ballet dancers than in sedentary groups of the same age. Furthermore, the responses were surprisingly smaller in the older ballet dancers than in the young sedentary group, at an equivalent level to that of the young ballet dancers. The influence of training, therefore, overcame the natural age-dependent changes. On the other hand, the onset latencies of the responses showed a solely age-dependent trend. Taken together, the present is the first to demonstrate that the motor memories in the spinal cord acquired through specific ballet training earlier in life can be maintained and carried forward in later life through further weekly participation in the same training.

High rebound mattress toppers facilitate core body temperature drop and enhance deep sleep in the initial phase of nocturnal sleep.

Recently, several new materials for mattresses have been introduced. Although some of these, such as low rebound (pressure-absorbing/memory foam) and high rebound mattresses have fairly different characteristics, effects of these mattresses on sleep have never been scientifically evaluated. In the current study, we have evaluated effects of a high rebound mattress topper [HR] on sleep and its associated physiology, and the effects were compared to those of a low rebound mattress toppers (LR) in healthy young (n = 10) and old (n = 20) adult males with a randomized, single-blind, cross over design. We found that sleeping with HR compared to LR induced a larger decline in core body temperature (CBT) in the initial phase of nocturnal sleep both in young (minimum CBT: 36.05 vs 36.35°C) and old (minimum CBT: 36.47 vs. 36.55°C) subjects, and declines in the CBT were associated with increases in deep sleep/delta power (+27.8% in young and +24.7% in old subjects between 11:00-01:00). We also found significantly smaller muscle activities during roll over motions with HR (-53.0 to -66.1%, depending on the muscle) during a separate daytime testing. These results suggest that sleeping with HR in comparison to with LR, may facilitate restorative sleep at the initial phase of sleep.

Evidence for existence of trunk-limb neural interaction in the corticospinal pathway.

In humans, trunk muscles have an essential role in postural control as well as walking. However, little is known about the mechanisms of interaction with different muscles, especially related to how trunk muscles interact with the limbs. Contraction of muscles can modulate the corticospinal excitability not only of the contracted muscle, but also of other muscles even in the remote segments of the body. However, "remote effect" mechanism has only been examined for inter-limb interactions. The aim of our current study was to test if there are trunk-limb interactions in the corticospinal pathways. We examined corticospinal excitability of: (a) trunk muscles at rest when hands, legs and jaw muscles were contracted and; (b) hand, leg, and jaw muscles at rest when trunk muscles were contracted. We measured motor evoked potentials elicited using transcranial magnetic stimulation in the rectus abdominis, flexor digitorum superficialis, masseter, tibialis anterior muscles under the following experimental conditions: (1) participants remained relaxed (Rest); (2) during trunk contraction (Trunk); (3) during bilateral hand clenching (Hands); (4) during jaw clenching (Jaw); and (5) during bilateral ankle dorsiflexion (Legs). Each condition was performed at three different stimulation intensities and conditions were randomized between participants. We found that voluntary contraction of trunk muscle facilitated the corticospinal excitability of upper-limb and lower-limb muscles during rest state. Furthermore, voluntary contraction of upper-limb muscle also facilitated the corticospinal excitability of trunk muscles during rest state. Overall, these results suggest the existence of trunk-limb interaction in the corticospinal pathway, which is likely depended on proximity of the trunk and limb representation in the motor cortex.

Dissociating the neural correlates of tactile temporal order and simultaneity judgements.

Perceiving temporal relationships between sensory events is a key process for recognising dynamic environments. Temporal order judgement (TOJ) and simultaneity judgement (SJ) are used for probing this perceptual process. TOJ and SJ exhibit identical psychometric parameters. However, there is accumulating psychophysical evidence that distinguishes TOJ from SJ. Some studies have proposed that the perceptual processes for SJ (e.g., detecting successive/simultaneity) are also included in TOJ, whereas TOJ requires more processes (e.g., determination of the temporal order). Other studies have proposed two independent processes for TOJ and SJ. To identify differences in the neural activity associated with TOJ versus SJ, we performed functional magnetic resonance imaging of participants during TOJ and SJ with identical tactile stimuli. TOJ-specific activity was observed in multiple regions (e.g., left ventral and bilateral dorsal premotor cortices and left posterior parietal cortex) that overlap the general temporal prediction network for perception and motor systems. SJ-specific activation was observed only in the posterior insular cortex. Our results suggest that TOJ requires more processes than SJ and that both TOJ and SJ implement specific process components. The neural differences between TOJ and SJ thus combine features described in previous psychophysical hypotheses that proposed different mechanisms.

Posture-related modulation of cortical excitability in the tibialis anterior muscle in humans.

Corticospinal excitability in the lower leg muscles is enhanced during standing as compared to other postures. In the present study, we investigated how the excitability of intracortical circuits that control the tibialis anterior muscle (TA) is modulated during standing. Short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were assessed by the paired-pulse transcranial magnetic stimulation technique during standing (STD) and sitting (SIT) with a comparable background activity level in both the soleus and the TA muscle. The results demonstrated that SICI was less effective during STD than during SIT, whereas ICF was more effective during STD than during SIT. These findings suggest that the excitabilities of these cortical neural circuits are modulated depending on posture. A decrease in SICI and an increase in ICF may reflect subliminal enhancement of the cortical excitability in the TA muscle during standing as compared with that during sitting.

Contraction history produces task-specific variations in spinal excitability in healthy human soleus muscle.

INTRODUCTION: In human movements muscles lengthen and then shorten, or occasionally shorten and then lengthen, but it is unclear whether the nature of neural activation of the initial phase influences the neural state of the subsequent phase. We examined whether contraction history modulates spinal excitability in the healthy human soleus muscle. METHODS: Subjects performed six blocks of 10 repetitions of four muscle actions consisting of specific combinations of passive shortening (PAS), and passive lengthening (PAL), shortening contraction (SHO), and lengthening contraction (LEN); that is: (1) SHO+PAL; (2) PAS+LEN; (3) PAS+PAL; and (4) SHO+LEN. RESULTS: Compared with baseline, the H-reflex increased in the block of 300-400 s after SHO+PAL and decreased in the block of 0-100 s after PAS+LEN and SHO+LEN. CONCLUSIONS: Our results suggest that spinal excitability is potentiated during a muscle action preceded by muscle shortening, but it becomes depressed during a muscle action preceded by muscle lengthening.

TMS-induced artifacts on EEG can be reduced by rearrangement of the electrode's lead wire before recording.

OBJECTIVE: Our purpose was to establish a technique to reduce residual artifacts after transcranial magnetic stimulation (TMS) from electroencephalographic (EEG) signals. METHODS: We investigated the effects of coil direction and stimulus intensity on residual artifacts in an artificial circuit, and tested whether or not the size of the circuit area affects the residual artifact (the model study). Based on the results, the optimization by rearranging the electrode's lead wire was tested on the human scalp (the human study). RESULTS: The residual artifact after TMS was dependent on the direction of the figure-of-eight coil, and on the artificial circuit area size. CONCLUSIONS: In accordance with the model study, the scalp EEG shows that TMS-induced artifacts can be reduced dramatically before the amplifier input stages in TMS-EEG experiments by a step-wise procedure rearranging the lead wires relative to the fixed coil orientation. SIGNIFICANCE: Our technique makes it possible to significantly reduce the residual artifacts from recordings of short-latency TMS-evoked potentials.

The role of the dorsolateral prefrontal cortex in the inhibition of stereotyped responses.

Stereotyped behaviors should be inhibited under some circumstances in order to encourage appropriate behavior. Psychiatrists have used the modified rock-paper-scissors (RPS) task to examine the inhibition of stereotyped behavior. When subjects are required to lose in response to a gesture, it is difficult for them to lose, and they have a tendency to win involuntarily. It is thought that the win response is the stereotyped response in the RPS task, and the difficulty in making positive attempts to lose is due to the requirement for inhibition of the stereotyped response. In this study, we investigated the brain regions related to inhibition of the stereotyped response using functional magnetic resonance imaging (fMRI). Subjects were assigned to one of two groups: the "win group" or the "lose group." The lose group showed higher activation of the left dorsolateral prefrontal cortex (DLFPC) when compared to the win group. We also delivered transcranial magnetic stimulation (TMS) while the subjects performed the modified RPS task to investigate whether the left DLPFC (middle frontal gyrus, Brodmann area, BA 9) was directly involved in the inhibition of the stereotyped response. When TMS was delivered before onset of the visual stimulus, the subjects displayed increased response errors. In particular, the subjects had a tendency to win erroneously in a lose condition even though they were required to lose. These results indicate involvement of the left DLPFC in inhibition of the stereotyped responses, which suggests that this region is associated with inhibition of the preparatory setting for stereotyped responses rather than inhibition of ongoing processing to produce a stereotyped response.

An fMRI study of musicians with focal dystonia during tapping tasks.

Musician's dystonia is a type of task specific dystonia for which the pathophysiology is not clear. In this study, we performed functional magnetic resonance imaging to investigate the motor-related brain activity associated with musician's dystonia. We compared brain activities measured from subjects with focal hand dystonia and normal (control) musicians during right-hand, left-hand, and both-hands tapping tasks. We found activations in the thalamus and the basal ganglia during the tapping tasks in the control group but not in the dystonia group. For both groups, we detected significant activations in the contralateral sensorimotor areas, including the premotor area and cerebellum, during each tapping task. Moreover, direct comparison between the dystonia and control groups showed that the dystonia group had greater activity in the ipsilateral premotor area during the right-hand tapping task and less activity in the left cerebellum during the both-hands tapping task. Thus, the dystonic musicians showed irregular activation patterns in the motor-association system. We suggest that irregular neural activity patterns in dystonic subjects reflect dystonic neural malfunction and consequent compensatory activity to maintain appropriate voluntary movements.

Enhanced excitability of the corticospinal pathway of the ankle extensor and flexor muscles during standing in humans.

The purpose of this study was to investigate how the recruitment properties of the corticospinal pathway are modulated in the soleus (SOL) and tibialis anterior (TA) muscles depending on postures. A wide range of stimulus intensities were applied via transcranial magnetic stimulation over the primary motor cortex during standing (STD) and sitting (SIT) with a comparable background activity level in each muscle. The relationship between the stimulation intensities and the size of motor-evoked potentials was assessed by the Boltzmann sigmoid function, which is characterized by a plateau value, maximum slope, and threshold. The plateau value and maximum slope were significantly higher during STD than during SIT in the SOL muscle (STD vs. SIT, plateau value: 50.0 +/- 21.8 vs. 33.9 +/- 12.3 mV ms, maximal slope: 1.6 +/- 0.7 vs. 1.2 +/- 0.5 mV ms/% maximal stimulator output). Similar changes of the parameters were also observed in the TA muscle (STD vs. SIT, plateau value: 71.0 +/- 22.9 vs. 41.4 +/- 16.1 mV ms, maximal slope: 5.0 +/- 2.0 vs. 2.5 +/- 0.7 mV ms/% maximal stimulator output). The threshold did not differ significantly between the two conditions and both muscles. These results indicate that the central nervous system requires a different control for each postural condition; that is, the relative balance of the excitatory and inhibitory inputs to the corticospinal pathways as well as the number of neurons of subliminal fringe in the corticospinal pathway was increased during STD compared with those during SIT.

Anterior prefrontal cortex activities during the inhibition of stereotyped responses in a neuropsychological rock-paper-scissors task.

Stereotyped responses must be suppressed at certain times during daily life, which can be difficult for patients with lesions in the frontal cortices. Neuropsychologists have used the rock-paper-scissors (RPS) task to evaluate patients' ability to suppress a stereotyped response. In this study, we measured functional magnetic resonance imaging signals to investigate how frontal cortex activities change corresponding to subjects' performance as they tried to lose (successfully inhibiting the typical response to win) when presented with a gesture signifying rock, paper, or scissors. Performance rates ranged from 50% to 100%, and results indicated that activation in the bilateral anterior part of the prefrontal cortex increased parametrically corresponding to subjects' successful performance. This result implies that the anterior prefrontal cortex plays a key role in the successful completion of a modified RPS task and may play a role in the suppression of stereotyped responses.

Enhanced stretch reflex excitability of the soleus muscle in experienced swimmers.

The purpose of this study was to investigate effects of long-term participation to swimming on adaptations of spinal reflex excitability. To this end, mechanically induced stretch reflex (SR) and electrically induced Hoffmann (H-) reflex of the soleus muscle were investigated between swimmers with experience of more than 10 years and non-trained individuals while sitting at rest. The amplitude and the gain (stretch velocity vs. amplitude of the reflex response) of the SR were significantly greater in the swimming group than in the non-trained control group. Similarly, the responses of the H-reflex were also significantly greater in the swimming group than in the non-trained control group. Results of this study demonstrated that the spinal reflex excitability in experienced swimmers was far more enhanced than in non-trained individuals.

Modulation of corticospinal excitability during lengthening and shortening contractions in the first dorsal interosseus muscle of humans.

Lengthening and shortening contractions are the fundamental patterns of muscle activation underlying various movements. It is still unknown whether or not there is a muscle-specific difference in such a fundamental pattern of muscle activation. The purpose of this study was, therefore, to investigate whether or not the relationship between lengthening and shortening contractions in the modulation of corticospinal excitability in the first dorsal interosseus (FDI) muscle is the same as that of previously tested muscles because the hand muscles are anatomically and functionally different from the other muscles. To this end, we investigated the relationship between the input-output curves of the corticospinal pathway (i.e., the relationship between the stimulus intensities vs. the area of motor-evoked potentials) during lengthening and shortening contractions in 17 healthy subjects. The shape of this relationship was sigmoidal and characterized by a plateau value, maximum slope, and threshold. The plateau value was at the same level between lengthening and shortening contractions. However, the maximum slope (P < 0.01) and threshold (P < 0.01) were significantly higher during lengthening contractions than during shortening contractions. These findings were different from the results of other muscles tested in previous studies (i.e., the soleus muscle and the elbow flexors). That is to say, the plateau value and the maximum slope during lengthening contractions were significantly lower than those during shortening contractions in previous studies. This study provides tentative evidence that the relationship between lengthening and shortening contractions in the modulation of corticospinal excitability differs between muscles, indicating that the underlying neural control is not necessarily the same even though the fundamental patterns of muscle activation are carried out.

Effects of loading and unloading of lower limb joints on the soleus H-reflex in standing humans.

OBJECTIVE: To investigate the effects of loading and unloading of the lower limb joints on the soleus H-reflex in standing humans. METHODS: H-reflexes were elicited in the soleus muscle in subjects standing on a force platform in a water tank under the following loading conditions of the ankle and knee joints: control condition; reduced loads of -10 and -20 N; imposed loads of 10 and 20 N. The joint loading was altered by changing the combinations of buoys and weights attached to the lower limb segments, while total body weight was kept constant. RESULTS: As the ankle- or knee-joint load was reduced, the H-reflex was significantly enhanced compared to that under the control condition. In contrast, the H-reflex was decreased as the ankle- or knee-joint load was increased. In both cases, similar levels of background activity were recorded. CONCLUSIONS: The present results suggest that joint afferents might mediate the suppression of the soleus H-reflex in standing humans. However, the identification of the receptors and/or the mechanisms cannot be addressed under the current experimental set up. SIGNIFICANCE: The results of this study give some basic insights into reflex control in an upright posture.

Differences in recruitment properties of the corticospinal pathway between lengthening and shortening contractions in human soleus muscle.

The purpose of this study was to investigate how the recruitment properties of the corticospinal pathway are modulated in the soleus muscle of the lower limb during lengthening (LEN) and shortening (SHO) contractions by comparing the shape of the input-output (I/O) relation of the corticospinal pathway. To this end, we investigated the relationship between various stimulus intensities applied via transcranial magnetic stimulation and the size of motor-evoked potentials in 14 healthy subjects during voluntary plantarflexion and dorsiflexion (active lengthening) with a similar background activity (BGA) level. The shape of this relationship was sigmoidal and was characterized by a plateau value, maximum slope and threshold. The plateau value was clearly lower during LEN contractions than during SHO contractions. Likewise, the maximum slope was lower during LEN contractions. However, the threshold did not differ significantly between the two tasks. Since the plateau value and the maximum slope clearly differed between LEN and SHO contractions despite the similarity of their BGA levels, the central nervous system appears to have a different activation strategy for each of these tasks. Namely, the relative balance between excitatory and inhibitory components of the corticospinal volleys, as well as the subliminal fringe of the corticospinal pathway, were reduced during LEN contractions compared with SHO contractions. These strategies may help to avoid reflexive contractions brought about by higher discharge of muscle spindles and enable fine motor actions in voluntary lengthening contractions.

Inhibition of the human soleus Hoffman reflex during standing without descending commands.

The purpose of the present study was to ascertain the contribution of peripheral sensory inputs to posture-related Hoffman reflex (H-reflex) modulation in the human soleus muscle. The soleus H-reflexes were elicited in the sitting (SI) and passive standing (ST) conditions in patients with clinically complete spinal cord injuries (SCI) and in neurologically normal subjects. The results clearly showed suppression of the H-reflex amplitude during the ST compared with the SI condition especially in the SCI group. Considering the lack of a descending neural command in the SCI patients, our findings suggest that peripheral sensory inputs primarily contribute to the reduction of the soleus H-reflex during the upright standing posture.