Influence of sports experience on distribution of pro-saccade reaction time under gap condition.

BACKGROUND: Previous studies indicated that substantial individual variation exists in the distribution of pro-saccade reaction times under gap condition. To investigate the influence of sports experience on the distribution, we examined distribution of the pro-saccade reaction time under overlap and gap conditions, for the basketball club, table tennis club, and non-sporting control groups. METHODS: Subjects performed pro-saccade tasks under the overlap and gap conditions, in which the intentional and reflexive disengagement of fixation are important, respectively. Under the overlap condition, the central fixation point was illuminated for a random duration of 1-3 s, then the fixation point was turned off. Just after the switch-off of the fixation point, one of the peripheral targets was illuminated for a duration of 1 s. The visual stimulus under the gap condition was almost the same as that under the overlap condition. However, only the temporal gap between the switch-off of the fixation point and the onset of the target differed between those conditions. The gap duration in the gap condition was set at 200 ms. The mean of median value of the bandwidth showing the earliest peak in the histogram was calculated for each group. Thereafter, for each subject, the bandwidth showing the earliest peak under the gap condition was defined as the criterion bandwidth (0 ms bandwidth). Based on this criterion bandwidth, the mean of the relative frequency was calculated for every 10 ms of bandwidth, for the overlap and gap conditions, in each group. RESULTS: Under the overlap condition, for all subjects, the pro-saccade reaction times showed unimodal distribution. The means of the median value of the bandwidth showing the earliest peak for the basketball and table tennis groups (approximate 170 ms) were significantly earlier than that for the control group (approximate 190 ms). Under the gap condition, the distribution was bimodal for 11 of 15 subjects in the basketball group and for 5 of 15 subjects in the control group. In the table tennis group, the distribution was not bimodal but unimodal for all 15 subjects. For the basketball group, mean of the relative frequency showed bimodal distribution with approximate 120 ms and 170 ms peaks. For the table tennis and control groups, the mean of the relative frequency showed unimodal distribution with approximate 130 ms and 140ms peak, respectively. CONCLUSIONS: The present study indicated that under the gap condition, the sports experience influenced on the distribution of the pro-saccade reaction time. The pro-saccade reaction time under the condition would show a distinct bimodal distribution for the basketball group and show a distinct and early unimodal distribution for the table tennis group. It was suggested that the physiological factor leading the group difference in the distribution was the effect of sports experience on the disengagement function of fixation.

Developmental changes in shortening of pro-saccade reaction time while maintaining neck flexion position.

BACKGROUND: We investigated developmental changes in shortening of pro-saccade reaction time while maintaining neck flexion. METHODS: Subjects comprised 135 children (3-14 years) and 29 young adults (19-23 years). Children were divided into six groups in 2-year age strata. Pro-saccade reaction tasks for 30 s were performed in neck rest and flexion positions. Reaction times under each position were averaged in every 10-s period. RESULTS: Under neck rest position, reaction time in the 0-10 s period was significantly longer in the 3- to 4-year-old group than in the 5- to 6-year-old group and above. No significant age effect was found for reaction time in the 0-10 s period in the 5- to 6-year-old group and above. Although a significant effect of neck flexion was not observed until the 9- to 10-year-old group, significant shortening of reaction time with neck flexion was found in the 11- to 12-year-old group and above. Furthermore, this shortening was maintained until the first 20-s period in the 11- to 12-year-old group and during the entire 30 s in the 13- to 14-year-old and above. CONCLUSIONS: These results suggest that brain activation with the maintenance of neck flexion, related to shortening of the pro-saccade reaction time, was found from a later age of approximately 11 years and above, compared with the age at which information-processing function in the pro-saccade was enhanced. In addition, brain activation with the maintenance of neck flexion was sustained longer with age.

Effect of maintaining neck flexion on anti-saccade reaction time: an investigation using transcranial magnetic stimulation to the frontal oculomotor field.

BACKGROUND: Reaction time for anti-saccade, in which the gaze is directed to the position opposite to an illuminated target, shortens during maintenance of neck flexion. The present study applied transcranial magnetic stimulation (TMS) to the frontal oculomotor field, and investigated the effect of maintaining neck flexion on information processing time in the anti-saccade neural pathway before the frontal oculomotor field. METHODS: The reaction time was measured with the chin resting on a stand ('chin-on' condition) and with voluntary maintenance of neck flexion ('chin-off' condition) at 80% maximal neck flexion angle, with and without TMS. The TMS timing producing the longest prolongation of the reaction time was first roughly identified for 10 ms intervals from 0 to 180 ms after the target presentation. Thereafter, TMS timing was set finely at 2 ms intervals from -20 to +20 ms of the 10 ms step that produced the longest prolongation. RESULTS: The reaction time without TMS was significantly shorter (21.9 ms) for the chin-off (235.9 ± 14.9 ms) than for the chin-on (257.5 ± 17.1 ms) condition. Furthermore, TMS timing producing maximal prolongation of the reaction time was significantly earlier (18.6 ms) for the chin-off than the chin-on condition. The ratio of the forward shift in TMS timing relative to the reduction in reaction time was 87.8%. CONCLUSIONS: We confirmed that information processing time in the anti-saccade neural pathway before the frontal oculomotor field shortened while neck flexion was maintained, and that this reduction time accounted for approximately 88% of the shortening of reaction time.

The effects of neck flexion on cerebral potentials evoked by visual, auditory and somatosensory stimuli and focal brain blood flow in related sensory cortices.

BACKGROUND: A flexed neck posture leads to non-specific activation of the brain. Sensory evoked cerebral potentials and focal brain blood flow have been used to evaluate the activation of the sensory cortex. We investigated the effects of a flexed neck posture on the cerebral potentials evoked by visual, auditory and somatosensory stimuli and focal brain blood flow in the related sensory cortices. METHODS: Twelve healthy young adults received right visual hemi-field, binaural auditory and left median nerve stimuli while sitting with the neck in a resting and flexed (20° flexion) position. Sensory evoked potentials were recorded from the right occipital region, Cz in accordance with the international 10-20 system, and 2 cm posterior from C4, during visual, auditory and somatosensory stimulations. The oxidative-hemoglobin concentration was measured in the respective sensory cortex using near-infrared spectroscopy. RESULTS: Latencies of the late component of all sensory evoked potentials significantly shortened, and the amplitude of auditory evoked potentials increased when the neck was in a flexed position. Oxidative-hemoglobin concentrations in the left and right visual cortices were higher during visual stimulation in the flexed neck position. The left visual cortex is responsible for receiving the visual information. In addition, oxidative-hemoglobin concentrations in the bilateral auditory cortex during auditory stimulation, and in the right somatosensory cortex during somatosensory stimulation, were higher in the flexed neck position. CONCLUSIONS: Visual, auditory and somatosensory pathways were activated by neck flexion. The sensory cortices were selectively activated, reflecting the modalities in sensory projection to the cerebral cortex and inter-hemispheric connections.

Effects of neck flexion on discriminative and cognitive processing in anticipatory postural control during bilateral arm movement.

We investigated the effect of neck flexion on discriminative and cognitive processing in postural control during bilateral arm movement while standing, using event-related potential (ERP) and electromyogram. Fourteen healthy subjects flexed their arms to the target stimuli with a 20% probability in neck resting and flexion positions. Amplitude and latency of N2 and P3, anterior deltoid (AD) reaction time, onset time of postural muscles with respect to AD activation, and peak amplitude and latency of all muscles were measured. With neck flexion, N2 and P3 amplitudes increased, N2 and P3 latencies and AD reaction time shortened, and onset times of all postural muscles became earlier. No significant differences in peak amplitude and latency of each muscle were found between neck positions. Significant positive correlations were found in changes with neck flexion between P3 latency and AD reaction time, and between N2 latency and onset time of erector spinae. These suggest that with neck flexion, attention allocation to discriminative and cognitive processing increased, and the processing speed increased with shortening of reaction time in focal muscles. In addition, the onset time of postural muscles became earlier without changing the activation pattern, which was associated with the hastened discriminative processing.

Eye movement performance and prefrontal hemodynamics during saccadic eye movements in the elderly.

No previous study has investigated age-related changes in prefrontal hemodynamics during saccade tasks in a large number of elderly adults. The purpose of this study was to evaluate prefrontal activity related to the performance of anti-saccade in the elderly using near-infrared spectroscopy (NIRS). Ninety-six elderly adults and 22 young adults performed pro- and anti-saccade tasks. Measures included reaction times of both saccades, error rate during anti-saccade, and concentration of oxyhemoglobin (Deltaoxy-Hb) in the prefrontal cortex during both saccades. Saccade performance, especially error rate, was significantly poorer in the elderly than the young. In the elderly, error rates were widely distributed from 5% to 100%. In about half (48%) of the elderly, error rates were distributed under the mean+3 standard deviations (48%) for the young, and Deltaoxy-Hb did not differ significantly from that in the young. Elderly subjects whose anti-saccade reaction time was over the regression line (of reaction time in anti-saccade to that in pro-saccade in the young)+2 standard errors showed a strong positive correlation (r=0.79) between Deltaoxy-Hb and error rate, as did those whose error rate exceeded 48%. In the elderly subjects whose error rates exceeded 90%, Deltaoxy-Hb was extremely small and deviated greatly from the correlation between Deltaoxy-Hb and error rate. Based on these findings, we propose a method of evaluating inhibitory function and attention allocation in anti-saccade performance, which is mainly related to the prefrontal cortex, in the elderly, using NIRS.

Changes in muscle thickness of gastrocnemius and soleus associated with age and sex.

BACKGROUND AND AIMS: Gastrocnemius and soleus in the triceps surae have functional and histological differences.We therefore investigated age-related changes in muscle thickness of these two muscles, as well as the difference in these changes between men and women. METHODS: Participants comprised 847 healthy adults aged 20 to 79 years. A B-mode ultrasound scanner, with participants sitting on a chair, was used to measure muscle thickness from the midpoint of the gastrocnemius medialis muscle at the level of maximum girth (target point). The ratio of muscle thickness to height was calculated. The inter-rater and intra-rater reliability of measuring muscle thickness with the ultrasound scanner and the validity of the target point were demonstrated before the examination. RESULTS: Gastrocnemius was significantly thinner in women aged 60 or older and in men aged 50 or older, compared with their counterparts in their 20s. For soleus, no significant differences in thickness were found among the age groups in either sex. Decline in muscle thickness from age 40-79 was greater for gastrocnemius than for soleus. CONCLUSIONS: These results confirm that gastrocnemius starts to deteriorate earlier and atrophies at a faster pace than soleus. A significant sex difference was found only in the onset age of gastrocnemius deterioration, which was earlier in men than in women.

Effect of vibration stimulation to neck extensor muscles on reaction time in various saccadic eye movements.

We investigated the effect of vibration stimulation to the neck extensors on reaction time in various saccades that are controlled by different higher neural system. Visually guided, memory-guided and anti saccades were performed under no-vibration and vibration (frequency, 100 Hz; amplitude, 0.5 mm) applied to the trapezius muscles. For memory-guided and anti saccades, the reaction time under the vibration was significantly shorter than that under no-vibration. A significant correlation was found between the shortening of reaction time for memory-guided saccade and that for visually guided saccade (r = 0.726, p <.01), but no significant correlation was found between anti-saccade and other saccades. These findings suggested that the higher saccadic neural pathway was strongly activated during the vibration stimulation to the neck extensors, and furthermore the effect of activation on facilitatory and inhibitory functions differed among the three types of saccades.

Neck-shortening effect on prosaccade reaction time formed through saccadic training accompanied by maintenance of neck flexion.

We investigated the effect of neck-shortening on prosaccade reaction time formed through saccadic training accompanied by maintenance of neck flexion. The subjects were 30 university students who exhibited no significant shortening of prosaccade reaction time during maintenance of neck flexion, assigned to three groups: prosaccade training subjects at rest neck position (rest training group); prosaccade training subjects at 20 degrees neck flexion position (neck training group); and untrained subjects (control group). Saccadic training for 1 min was performed ten times per day, and the training period was 14 days. For the control group, no significant postural or training effects on reaction time were found. For both training groups, reaction time at the rest position after training was significantly shorter than that before training. For the neck training group, reaction time after training was significantly shorter at the neck flexion position than at the rest position. Conversely, no significant neck effect was found for the rest training group. This indicates that the shortening effect associated with maintenance of neck flexion on prosaccade reaction time is formed through saccadic training accompanied by maintenance of neck flexion.

Increase in corticospinal excitability of limb and trunk muscles according to maintenance of neck flexion.

The effect of maintenance of neck flexion on corticospinal excitability of limb and trunk muscles was investigated using transcranial magnetic stimulation (TMS). Nine healthy young subjects participated in this experiment. Every measurement was performed with subjects sitting on a chair. Target muscles were the first dorsal interosseous (FDI), biceps brachii (BB), triceps brachii (TB), rectus abdominis (RA), erector spinae (ES), rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and gastrocnemius (GcM) on the right side. TMS was applied to the left primary motor cortex, and motor evoked potential (MEP) was measured from the muscles listed above. Optimal stimulus location and resting motor threshold (RMT) were identified for each target muscle, and stimulus intensity used was 120% of RMT. MEPs of the target muscle were recorded with the chin resting on a chin support (chin-on condition) with neck in 20 degrees of flexion, and with voluntary maintenance of the neck flexion posture (chin-off condition). Amplitude and latency of MEP and background activity of target muscles were analyzed. For FDI, BB, TB, ES, and RF, amplitude of MEP increased and latency shortened in the chin-off compared with the chin-on condition. No significant difference in background activity of each target muscle was found between the two conditions. Corticospinal excitability of limb and trunk muscles was selectively enhanced while neck flexion was maintained.

Effects of neck flexion on contingent negative variation and anticipatory postural control during arm movement while standing.

We investigated the effects of neck flexion on contingent negative variation (CNV) and anticipatory postural control using an arm flexion task in standing. CNV was adopted to evaluate the state of activation of brain areas related to anticipatory postural control. Subjects were required to flex the arms in response to a sound stimulus preceded by a warning sound stimulus. Two different intervals (2.0 and 3.5s) between these two stimuli were used in neck position in quiet standing (neck resting) and neck position at 80% angle of maximal neck flexion. The mean amplitude of CNV 100-ms before the response stimulus, recorded from a Cz electrode, was calculated. Onset timing of activation of the postural muscles (lumbar paraspinal, biceps femoris and gastrocnemius) with respect to the anterior deltoid was analyzed. Reaction time at the anterior deltoid was significantly shorter in the 2.0s period than in the 3.5s period, and in the neck flexion than in the neck resting in both periods. In the 2.0s, but not in the 3.5s period, neck flexion resulted in an increased CNV amplitude and an increased duration of preceding activation of the postural muscles, and the correlation between these increases was significant.

Changes in the activity of the cerebral cortex relate to postural response modification when warned of a perturbation.

OBJECTIVE: To determine whether the cerebral cortex contributes to modifying upcoming postural responses to external perturbations when provided with prior warning of the perturbation. METHODS: Electroencephalographic (EEG) potentials were recorded from 12 healthy human subjects (21-32 years of age) before perturbing their balance with backward translations of a platform under their feet. The subjects responded with and without a visual cue that warned them 2s before the perturbation (the Cue and No Cue conditions, respectively). RESULTS: Contingent negative variation (CNV) was evident before perturbation onset in only the Cue condition. In the Cue condition, the subjects also produced smaller center of pressure (CoP) displacements than in the No Cue condition. The cue-related difference in the subjects' CNV potentials correlated with the cue-related difference in their CoP displacements. No significant associations existed among the CNV potentials and any cue-related postural adjustments made before the perturbation. CONCLUSIONS: Cortical activity before an externally triggered perturbation associates with modifications of the ensuing postural response. SIGNIFICANCE: This is the first study to demonstrate a cortical correlate for changes in central postural set that modify externally triggered postural responses based on anticipation.

Postural movement pattern and muscle action sequence associated with self-paced bilateral arm flexion during standing.

Investigated were postural movement pattern and action sequence of postural muscles while subjects rapidly flexed both arms during standing. The arm movement was started at the subject's own pace. Subjects were healthy individuals; 48 men and 53 women. Postural movement pattern was classified based on the movement angles of foot-leg (ankle joint) and leg-trunk (hip joint). Electromyograms were recorded from the anterior deltoid, biceps femoris, and erector spinae. The time difference between action onsets of the latter two muscles and the anterior deltoid was analyzed. Movement angles of the ankle and hip for both sexes were distributed on a similar linear regression line (y = -2.092x - 2.552 (r = -.71). The postural movement pattern was categorized based on the distribution into three types: hip flexion (in the 2nd quadrant), backward leaning (the 3rd), and hip extension (the 4th). The proportion of subjects was 26% in the hip flexion type, 55% in backward leaning type, and 19% in hip extension type. The action of biceps femoris and erector spinae significantly preceded that of anterior deltoid in the backward leaning and hip extension types but did not in the hip flexion type.

Optimal vibration stimulation to the neck extensor muscles using hydraulic vibrators to shorten saccadic reaction time.

Optimal vibration stimulation to the neck extensor muscles using hydraulic vibrators to shorten the saccadic reaction time was examined. Subjects were 14 healthy young adults. Visual targets (LEDs) were located 10 degrees left and right of a central point. The targets were alternately lit for random durations of 2-4 seconds in a resting neck condition and various vibration conditions, and saccadic reaction times were measured. Vibration amplitude was 0.5 mm in every condition. The upper trapezius muscles were vibrated at 40, 60, 80, and 100 Hz in a sub-maximum stretch condition in which the muscles were stretched at 70% of maximum stretch. In addition, the muscles were vibrated at 60 Hz with the muscles maximally stretched, with 70% vertical pressure without stretching, and with vibration applied to the skin in the same area as the muscle vibration. At 60, 80, and 100 Hz at 70% maximum stretch, saccadic reaction time shortened significantly compared with the resting neck condition. However, no significant difference in the reaction time was observed among the frequencies. The saccadic reaction times in the maximum stretch condition, muscle pressure condition, and skin contact condition did not differ significantly from that in the resting neck condition. Vibration stimulation to the trapezius with 60-100 Hz frequencies at 0.5 mm amplitude in the sub-maximum stretch condition was effective for shortening saccadic reaction time. The main mechanism appears to be Ia information originating from the muscle spindle.

Changes in saccadic reaction time while maintaining neck flexion in the elderly.

We investigated changes in saccadic reaction time during maintenance of neck flexion in elderly individuals. Subjects comprised 49 volunteers, including 19 young adults and 30 elderly adults. Elderly subjects were separated into 2 groups (trained group: n=18; untrained group: n=12) based on responses to a questionnaire concerning activities of daily living. Saccadic reaction time was measured at angles of neck flexion of 0 degrees (resting position), 10 degrees and 20 degrees , with the chin either resting on a stand (chin-on) or not (chin-off). Reaction time was determined as the latency to the beginning of eye movement toward the lateral target, which was moved at random intervals in jumps of 20 degrees amplitude. In the chin-on posture, the angle of neck flexion had no significant effect on reaction time in any group. In the chin-off posture, the flexion angle significantly affected reaction time in both young and elderly trained groups. Significant shortenings of the reaction time were obtained at 10 degrees and 20 degrees neck flexion in the young group, and at 20 degrees neck flexion in the elderly trained group. No significant shortening of reaction time was noted in the elderly untrained group. These findings suggest that neural function associated with shortening of saccadic reaction time due to neck extensor activity decreases with age, and the decrements become more marked with inactivity in daily life.

Changes in the P100 latency of the visual evoked potential and the saccadic reaction time during isometric contraction of the shoulder girdle elevators.

We investigated changes in the P100 latency of the visual evoked potential (VEP) and the saccadic reaction time (SRT) in relation to the degree of activity of the shoulder girdle elevators. Muscle force was set in 10% increments from 0% to 50% of the maximal voluntary contraction (MVC). The VEP was derived from a midline occipital electrode with reference electrodes on the ears when the right retina was stimulated through the eyelid by light emitting diodes while the eyes were closed. The P100 latency of the VEP was defined as the time from the stimulus onset to the main positive peak. The SRT was defined as the latency until the beginning of eye movement toward the lateral target, which was moved at random time-intervals. P100 latency was shortened until 30% of the MVC, and which it lengthened. The SRT changed in a pattern similar to that observed for the P100 latency. The ratio of the shortening in P100 latency relative to that of the SRT was approximately 20%. All data is presented as the mean value, plus the standard deviation. We believe that the information processing time in the neural pathway from the retina to the visual cortex was shortened up to a certain muscle force of the shoulder girdle elevators, and then this processing time lengthened. These findings indicate that shortening of information processing time in the neural pathway beyond the visual cortex is included in the shortening of the SRT.

Perceived standing position after reduction of foot-pressure sensation by cooling the sole.

We investigated the influence of the reduction of foot-pressure sensation by cooling the sole of the foot, at 1 degree C for 30 or 40 minutes, on the perception of standing position varied in the anteroposterior direction. The subjects were 16 healthy undergraduates. Firstly, for 4 of the subjects, cooling the sole of the foot decreased sensory information from the mechanoreceptors in the sole, by testing for an increase in the threshold for two-point discrepancy discrimination on the sole of the foot and for the disappearance of postural change with vibration to the sole. Next, the perception of standing position was measured by reproduction of a given standing reference position involving forward or backward leaning under both normal and cooled conditions of the feet. Standing position was varied in relation to the location of the center of foot pressure, defined as distance from the heel in percentage of the length of the foot. The reference positions, representing various locations of the center of foot pressure, were set at 10% increments from 20% to 80% of the length of the foot. With eyes closed, the subject first experienced the reference position and then attempted to reproduce it. The mean location of the center of foot pressure in the quiet standing posture was 45.7%. At the 40%, 50%, and 60% reference positions, those closest to quiet standing, absolute errors of reproduction were significantly larger than at other reference positions in both the normal and the cooled conditions. They were significantly larger in the cooled than in the normal condition. The 50% and 60% reference positions were reproduced significantly further forward in the cooled than in the normal condition. These results may be explained as due to an absence of marked changes in sensory information from both muscular activity and foot pressure when moving to reference positions close to the quiet standing posture.

Anticipatory activation of postural muscles associated with bilateral arm flexion in subjects with different quiet standing positions.

We investigated changes in activation timing and magnitude of the postural muscles according to initial standing positions. The subjects were divided into three groups depending on the position of the center of foot pressure (CFP) during quiet standing, namely backward, middle, and forward. Subjects maintained standing postures at various CFP positions in the anteroposterior direction, and then started bilateral arm movement at their own pace. The activation magnitude of the biceps femoris (BF) and erector spinae (ES) did not differ among any of the initial CFP positions. In only the BF, the preceding action to the anterior deltoid (AD) was clearly observed at more forward CFP positions in the order of the forward, middle and backward groups. Between initial CFP positions adjacent to quiet standing posture, the smallest change was observed in the preceding activation time of the BF. Significant correlation was observed between the background activity and activation time in both the BF and ES.

Latency of saccadic eye movement during contraction of bilateral and unilateral shoulder girdle elevators.

We compared the timed latencies of saccadic eye movement during isometric contraction of the bilateral and unilateral shoulder girdle elevators in a sitting posture. Muscle contraction force was increased in 10% increments from 0% to 60% of the maximal voluntary contraction (MVC) of each side. Saccadic latency was measured as the latency to the beginning of eye movement toward the lateral target that was moved at random intervals in 20 degree amplitude jumps. Eye movement was measured using the electro-oculogram technique. During bilateral contraction, saccadic latency decreased until 30% MVC and then began to increase at 40% MVC. During unilateral contraction, saccadic latency decreased until 30% MVC in a similar pattern as in bilateral condition, was constant from 30% MVC to 50% MVC, followed by a slight increase at 60% MVC. The saccadic latencies at 10% and 40-60% MVC were significantly shorter during unilateral contraction than bilateral contraction. Thus, the relative force for producing a marked shortening of saccadic latency is observed within a wider range during unilateral contraction than bilateral contraction.