Tateo Warabi

Effect of aging on sensorimotor functions of eye and hand movements

Changes in coordinated eye and hand movements with aging were studied in normal young and elderly subjects. Electrooculograms, flexor and extensor electromyograms, and potentials representing hand movements were recorded and used to evaluate the performance in aiming tasks. The parameters that reflect motor functions did not change significantly with aging in both eye and hand movements. However, elderly subjects commonly showed increases in reaction times of the initial (open-loop) movements in both eye and hand movements. Interestingly, the time increments were almost equivalent in these two functionally distinct motor systems. The durations of error-correcting (closed-loop) movements also increased significantly with aging in both motor systems. These increases suggest that the aging effects are the manifestation of impairment in the sensory process.

Treadmill walking and overground walking of human subjects compared by recording sole-floor reaction force

In order to clarify differences of treadmill from overground locomotion, experiments were carried out on 10 volunteers (five males and five females). Sole-floor reaction force was recorded from five anatomically discrete points with strain gauge transducers of 14 mm diameter attached firmly to the sole of bare-foot. At first the subject was asked to walk on the laboratory floor at his/her preferred velocity. After the average velocity was obtained, the subject was asked to walk on the treadmill at the same velocity of average overground walking. Stance period at treadmill walking shortened to 93.3% (P < 0.01) of the value at overground walking. Coefficient of variation of stance period was significantly smaller at the treadmill walking than at overground walking. Strain gauge-floor contact times were shorter in the treadmill walking; heel 81.2%, first metatarsal 93.5%, third metatarsal 93.6%, fifth metatarsal 90.6% and at great toe 93.2% of overground locomotion. Cadence during treadmill locomotion was significantly larger than overground walking (106.6%, P < 0.05). These results show that when subjects walk on the treadmill and on laboratory floor at the identical speed, stance period shortened by 6.7% while cadence increased by 6.6% on the treadmill.

The reaction time of eye-head coordination in man

Abstract The reaction time of eye-head coordination was studied in man in connection with different target angles. Both the reaction time of the electromyographic activity in neck and that for the saccadic eye movement increased with increase of visual target angles. The increases of these two reaction times are parallel, with a remaining constant separation around 45 msec. Head movement followed the saccade with an interval of 20–40 msec irrespective of the target angles. The observed increase of reaction time is too large to be explained by intraretinal conduction time. It is postulated to reflect a central mechanism involved in eye-head coordination.

Medial-lateral balance during stance phase of straight and circular walking of human subjects.

Right and left balance during human locomotion has been estimated by the distance between locations of the sequential right and left heel-strikes, or step width. During the stance phase of human locomotion one leg maintains medial-lateral balance for the progression. We focused our attention on this point, and medial-lateral balance during straight-ahead and circular walking was investigated by recording sole-floor reaction force from five anatomically discrete points of human sole; calcaneus, 1st, 3rd, 5th metatarsals and great toe. Forces from these points were recorded during straight walking and circular walking. Medial-lateral balance was obtained by subtracting force at 5th metatarsal from force at 1st metatarsal (x-axis vector). The foot takes off the floor from medial balance in most steps, although in some steps the foot takes off from lateral balance at slower walking speed at 2 km/h or 4 km/h, showing variable patterns of x-axis vector. At faster walking speed at 6 km/h or 8 km/h body weight shifted to 1st metatarsal before taking off the floor. During circular walking body weight shift to 1st metatarsal in the outer foot, and to 5th metatarsal in the inner foot in most cases.

Vestibular-related frontal cortical areas and their roles in smooth-pursuit eye movements: representation of neck velocity, neck-vestibular interactions, and memory-based smooth-pursuit.

Smooth-pursuit eye movements are voluntary responses to small slow-moving objects in the fronto-parallel plane. They evolved in primates, who possess high-acuity foveae, to ensure clear vision about the moving target. The primate frontal cortex contains two smooth-pursuit related areas; the caudal part of the frontal eye fields (FEF) and the supplementary eye fields (SEF). Both areas receive vestibular inputs. We review functional differences between the two areas in smooth-pursuit. Most FEF pursuit neurons signal pursuit parameters such as eye velocity and gaze-velocity, and are involved in canceling the vestibulo-ocular reflex by linear addition of vestibular and smooth-pursuit responses. In contrast, gaze-velocity signals are rarely represented in the SEF. Most FEF pursuit neurons receive neck velocity inputs, while discharge modulation during pursuit and trunk-on-head rotation adds linearly. Linear addition also occurs between neck velocity responses and vestibular responses during head-on-trunk rotation in a task-dependent manner. During cross-axis pursuit–vestibular interactions, vestibular signals effectively initiate predictive pursuit eye movements. Most FEF pursuit neurons discharge during the interaction training after the onset of pursuit eye velocity, making their involvement unlikely in the initial stages of generating predictive pursuit. Comparison of representative signals in the two areas and the results of chemical inactivation during a memory-based smooth-pursuit task indicate they have different roles; the SEF plans smooth-pursuit including working memory of motion–direction, whereas the caudal FEF generates motor commands for pursuit eye movements. Patients with idiopathic Parkinson’s disease were asked to perform this task, since impaired smooth-pursuit and visual working memory deficit during cognitive tasks have been reported in most patients. Preliminary results suggested specific roles of the basal ganglia in memory-based smooth-pursuit.

Posterior-anterior body weight shift during stance period studied by measuring sole-floor reaction forces during healthy and hemiplegic human walking.

Posterior-anterior body weight shift during stance phase of human overground locomotion was investigated by recording sole-floor reaction force from five anatomically discrete points with strain gauge transducers of 14 mm diameter attached firmly to the sole of bare foot. At first the subject was asked to walk straight on the laboratory floor at his/her preferred velocity. Then the subject was asked to walk curved path of about 1m radius. For kicking off the body at the end of stance phase, sole-floor reaction force from 3rd metatarsal was stronger than 1st metatarsal or 5th metatarsal during the straight walking, thus body weight shift is represented from heel to 3rd metatarsal line. When walking along a curved path, two types of strategies were recognized; a group of subjects walked leaning to inner leading foot during stance period as judged by stronger forces recorded from 5th metatarsal combined with stronger force from 1st metatarsal of outer trailing foot. Another group of subjects showed almost the same patterns either in the straight and curved walking, suggesting the subjects changed direction of the foot during the immediately previous swing phase to the tangent direction of the curve and placed the foot without leaning the body weight to either direction. Hemiplegic patients showed strikingly different distribution of sole-floor reaction forces from the five points; strongest forces were recorded from 3rd and 5th metatarsals combined with reduced reaction force from heel, therefore characteristic y-vector patterns were observed.

Progression of human body sway during successive walking studied by recording sole-floor reaction forces.

Strain gauge transducers were firmly attached to five points of the human sole: calcaneus, 1st, 3rd, and 5th metatarsals and great toe. Forces from these five points were recorded during treadmill walking at different speeds. With this method it is possible to obtain data of several dozen steps successively. Lateral-medial force change (x-vector) during progression was obtained from the 5th and 1st metatarsals and posterior-anterior force change (y-vector) was obtained from the calcaneus and 3rd metatarsal. Lateral balance and medial balance were differentiated in x-vector and rearfoot phase and forefoot phase were distinguished in y-vector. The percentage of the forefoot phase among the stance period shows a linear increase with speed of progression. It was concluded that the phase of body sway forward is regulated by walking speeds.

Difficulty in terminating the preceding movement/posture explains the impaired initiation of new movements in Parkinson's disease.

To determine whether the difficulty of initiating volitional movements in Parkinsons disease is primarily due to impaired termination of preceding movement/posture or to impaired initiation of new movement, patients with Parkinsons disease and age-matched controls were first asked to visually fixate a stationary spot and simultaneously align wrist position accurately with it. They were then requested to make rapid movements of eyes and wrist to a test stimulus presented in the peripheral visual field. We analyzed latencies of ocular and manual movements to the test stimulus in two conditions; in the overlap task the stationary spot remained on during illumination of the test stimulus requiring subjects to terminate fixation and wrist positioning themselves to initiate new movements. In the gap task, the stationary spot was turned off 200 ms before illuminating the test stimulus. Latencies of ocular and manual movements were prolonged in the overlap task than those in the gap task. Effects of fixation/wrist positioning on the latency of new movement were evaluated by the difference in latencies between the overlap and gap tasks normalized by the latency difference of the controls. These ratios increased exponentially as Parkinsons stage increased, suggesting the latency prolongation in patients with stage III and IV Parkinsons disease under the overlap condition primarily reflected the contribution of difficulty to terminate existing fixation/wrist positioning.

Effects of stroke-induced damage to swallow-related areas in the brain on swallowing mechanics of elderly patients

Aim:u2003 Our objective was to determine the relationship between defective swallowing mechanics and the location of brain lesions in stroke patients.

Trunk-ocular reflex in man.

The experiments were designed to determine whether twisting of the trunk induces eye movements in man. The subjects head and neck were fixed firmly, and the chair in which the subject sat was turned along a vertical axis sinusoidally at about 1 4 Hz . It was found that the eye deviated horizontally in a direction counter to the twisting of the lower trunk. This ocular movement was accompanied by nystagmus. The gain (the ratio of ocular movement to chair movement) of the trunk-ocular reflex appeared to be about 0.5 with time lag of around 80 msec.