Naoe Kiyota

Adaptation changes in dynamic postural control and contingent negative variation during backward disturbance by transient floor translation in the elderly

BackgroundWe investigated adaptation changes in dynamic postural control and contingent negative variation (CNV) in 13 young and 12 elderly adults. Subjects repeatedly underwent backward postural disturbance by a forward floor translation (S2) 2 s after an auditory warning signal (S1). Initial and second sets were conducted, each set with 20 trials. Posterior peak position of the center of pressure in the anteroposterior direction (CoPy) after S2 was identified. Electroencephalograms from Cz were averaged for each set, and the CNV negative peak was identified.ResultsCompared with the first trial, the posterior peak position of CoPy changed significantly forward from the 12th trial in the young and from the 19th trial in the elderly during the initial set. The mean of the posterior peak position was more forward in second set than in the initial set for both groups and was significantly backward in the elderly compared to the young for both sets. These findings indicate that subjects in both groups adapted better to the postural disturbance in the second set than in the initial set, and the adaptation was later in the elderly. Late CNV in the young started to increase negatively from the middle of the S1-S2 period and peaked just before S2. Peak CNV amplitude was larger in the second set than in the initial set. In contrast, late CNV in the elderly exhibited no negative increase as in the young and peaked in the middle of the S1-S2 period, which was followed by gradual decreasing toward S2. No adaptive changes were found in late CNV for the elderly.ConclusionsIt is conceivable that reduced activation of the frontal lobe may be one of the factors contributing to the decrease in postural adaptability in the elderly. The elderly may use various brain regions for the adaptation of dynamic postural control compared with the young.

Changes in event-related potentials associated with postural adaptation during floor oscillation.

The event-related potential (ERP) mainly reflecting activation of the frontal lobe was measured during periodic floor oscillation, and changes in postural preparation and attention to the postural disturbance according to this adaptation were investigated. The experiment consisted of two tasks with eyes closed: adaptation to floor oscillation and finger flexion coinciding with the anterior and posterior reversals of oscillation. Subjects were 20 healthy young adults. They maintained a standing posture for 1 min (1 trial) on the force platform which oscillated in the anteroposterior direction at 0.5 Hz and an amplitude of 2.5 cm. ERP from a Cz electrode, activity of postural muscles and the center of foot pressure in the anteroposterior direction (CoPy) were analyzed. In the adaptation task, the speeds of CoPy fluctuation gradually decreased and reached a plateau between 4th and 14th trials, with inter-subject differences. Posterior postural muscles were activated in response to the anterior reversal of oscillation according to adaptation and also in the finger flexion task, with the largest activation of the gastrocnemius (GcM). A negative ERP peak was observed to occur locally around the anterior reversal of oscillation after adaptation. The peak ERP time had the strongest positive correlation with the peak activation time of the GcM, and the amplitude of the negative peak decreased with adaptation. In the finger flexion task, a negative ERP peak was observed around each target point. This negative peak was related to the anticipatory attention directed to the reversal point and to motor preparation for finger flexion. It is conceivable that the increasing negative ERP in the adaptation task reflects the dynamics of motor preparation and attention mainly for the anterior reversal, where the negative ERP peak is closely related to anticipatory information processing of somatosensory stimuli arising around the time of the reversal.

Adaptation changes in dynamic postural control and contingent negative variation during repeated transient forward translation in the elderly

BackgroundAdaptation changes in postural control and contingent negative variation (CNV) for the elderly were investigated during repeated forward floor translation.MethodsFifteen healthy elderly persons, living in the suburban area of Kanazawa City, Japan, underwent backward postural disturbance by a forward-floor translation (S2) 2 s after an auditory warning signal (S1). A set with 20 trials was repeated until a negative peak of late CNV was recognized in the 600-ms period before S2, and the last set was defined as the final set. Electroencephalograms, center of foot pressure in the anteroposterior direction (CoPap), and electromyograms of postural muscles were analyzed.ResultsCoPap displacement generated by the floor translation was significantly decreased until the twelfth trial in the first set, and mean CoPap displacement was smaller in the second and final sets than in the first set. The mean displacement was significantly smaller in the final set than the previous set. A late CNV with a negative peak was not recognized in the first and second sets. However, most subjects (13/15) showed a negative peak by the fourth set, when the late CNV started to increase negatively from about 1,000 ms after S1 and peaked at about 300 ms before S2. At about 160 ms before the CNV peak, the CoPap forward shift started. The increase in timing of the gastrocnemius activity related to the CoPap shift was significantly correlated with the CNV peak timing (r = 0.64). After S2, peak amplitudes of the anterior postural muscles were significantly decreased in the final set compared to the first set.ConclusionsIt was demonstrated that even for the elderly, with so many repetitions of postural disturbance, a late CNV with a negative peak was recognized, leading to accurate postural preparation. This suggests the improvement of frontal lobe function (e.g., anticipatory attention and motor preparation) in the elderly.

Postural control during transient floor translation while standing with the leg and trunk fixed

Postural movement was restricted above the ankle, and contingent negative variation (CNV) and postural muscle activity were investigated during a transient floor translation (S2) 2s after an auditory warning signal (S1). For 13 healthy young adults, the joints of the knee, hip, and trunk were fixed using a cast brace. Under no-fixation and fixation, a set of 10 translations was repeated at least 4 times, and center of pressure in the anteroposterior direction (CoPap), posterior postural muscle activity of the body (elector spinae (ES), biceps femoris (BF), gastrocnemius (GcM) and soleus (Sol)), and late CNV at Cz were analyzed in the initial two sets (initial set) and last two sets (late set). In the no-fixation, CoPap forward displacement after S2 gradually decreased. In the first trial of the fixation, it had significantly increased, and then rapidly decreased across subsequent trials. CNV peak amplitude was largest in the late set of the fixation. The activity of postural muscles increased just before S2 and in the late set the start time showed high correlations with CNV peak time in all muscles (ES (r=0.88), BF (0.92), GcM (0.80), and Sol (0.89)) under the no-fixation, but exclusively in the GcM (0.84) and Sol (0.88) under the fixation. When postural control was restricted mainly to the ankle, attention would have been focused mainly on processing sensory information from the triceps surae just before the floor translation.

Postural responses to various frequencies of vibration of the triceps surae and forefoot sole during quiet standing.

The purpose of this study was to determine the role of somatosensory input to the sensory reference system in quiet standing. We applied vibration (0.5 mm amplitude, 1–60 Hz) to the triceps surae and the forefoot sole to stimulate the muscle spindles and the mechanoreceptors, respectively, and evaluated postural responses. Thirteen young healthy adults who showed backward-lean and forward-lean responses to vibration at high and low frequencies, respectively, participated in the full experiment. The lowest vibration frequencies inducing backward-lean responses (B-LF) were 15–55 Hz for the triceps surae and 16–60 Hz for the forefoot sole. The highest frequencies inducing forward-lean responses (F-HF) were 3–18 Hz for the triceps surae and 1–20 Hz for the forefoot sole. When vibration was simultaneously applied to the triceps surae and forefoot sole at F-HF, no response was induced in 70% of trials. A forward-lean response was induced in the remaining 30% of trials. Simultaneous vibration of the triceps surae and forefoot sole at B-LF induced backward-lean responses in all trials. All postural responses occurred 0.5–4.3 s after vibration onset. Postural responses to highfrequency vibration conceivably occur as a compensatory movement to the illusionary perception that standing position is deviating forward from quiet standing, which must be a reference position. Postural responses to low-frequency vibration possibly occur to equalize the positional information that is received from the triceps surae and the forefoot sole. Both postural responses are likely to involve the sensory reference system, which is located in the supraspinal nervous system.

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

BackgroundA 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.MethodsTwelve 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.ResultsLatencies 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.ConclusionsVisual, 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.

Postural Responses Accompanying Achilles Tendon Vibration Stimulation during Various Phases of Sit-to-Stand Movement

The aim of this study was to determine the postural response accompanying Achilles tendon vibration stimulation during various phases of the sit-to-stand movement. Twelve healthy young adults performed the sit-to-stand movement in response to an auditory signal 2 s after a first one. Vibration stimulation with a 100 Hz frequency was applied to both Achilles tendons during the following phases: (1) 10 s of sitting before standing up; (2) 10 s plus a period until the standing position was achieved; and (3) 5 s after standing. The postural response after standing was analyzed with the center of foot pressure in the anteroposterior direction. Forward-leaning responses were identified in 78.3% and 63.3% of trials under conditions 1 and 2, respectively. Backward-leaning responses were identified in 93.3% of the trials under condition 3. Response latency (± standard deviation) was significantly longer under conditions 1 and 2 than under condition 3 (1: 872 ± 576, 2: 1026 ± 542, and 3: 555 ± 322 ms; ps < 0.05). Sensory information at the standing point might be anticipated based on sensory information received while sitting. Consequently, postural response as a compensatory movement would occur via the sensory reference system within the supraspinal nervous system.