Movement related potentials in acutely induced weakness and stroke.

Weakness is a common symptom of neurological illness, and recovery may occur via restorative or compensatory mechanisms. Functional imaging studies have shown varied patterns of activity in motor areas following recovery from stroke. Movement related potentials (MRP) reflect the activity in primary and non-primary motor areas.

Motor unit excitability changes mediating vestibulocollic reflexes in the sternocleidomastoid muscle.

Objective: To investigate the patterns of motor unit firing in single motor units from the sternocleidomastoid (SCM) muscles in response to stimuli previously shown to be capable of evoking vestibulocollic reflexes (loud clicks and electrical stimulation) and to relate these to the previously described surface potentials (VEMPs, vestibular evoked myogenic potentials) evoked by the same stimuli.

Methods: Eleven male subjects (30-43-years-old) were studied. Local anaesthetic was used to block the SCM and confirm that the surface potentials (p13n23) arose from it.

Sway patterns in a case of orthostatic tremor responsive to alcohol.

We describe changes in the extent of sway in a man with orthostatic tremor (OT) who reported increased stability after alcohol. He was tested at baseline and again after 40 g (0.5 g/kg) of alcohol.

Evidence for reflex and perceptual vestibular contributions to postural control.

Vestibular signals are known to have an important role in stance under specific conditions. Potentially these effects could be modulated by vestibular reflexes or by voluntary responses to perceived vestibular signals. Our preliminary aim was to confirm that vestibulospinal reflexes change in parallel with sway under different postural conditions, and then to determine whether any relationship was present between these reflexes and body sway within fixed postural conditions.

Vestibular activation by bone conducted sound.

Objective: To examine the properties and potential clinical uses of myogenic potentials to bone conducted sound.

Methods: Myogenic potentials were recorded from normal volunteers, using bone conducted tone bursts of 7 ms duration and 250-2000 Hz frequencies delivered over the mastoid processes by a B 71 clinical bone vibrator. Biphasic positive-negative (p1n1) responses were recorded from both sternocleidomastoid (SCM) muscles using averaged unrectified EMG.

Anodal vestibular stimulation does not suppress vestibular reflexes in human subjects.

Anodal current applied to the vestibular apparatus has previously been found to inhibit discharge from irregular vestibular afferents in squirrel monkeys. We wished to investigate whether anodal currents applied over the mastoid processes of human subjects would significantly reduce ongoing vestibular activity and thereby the size of galvanic-evoked vestibulospinal reflexes, measured by soleus electromyogram. Nine subjects were tested, of whom six subjects (five females, one male) provided data for the final analysis.

Galvanic and acoustic vestibular stimulation activate different populations of vestibular afferents.

Objective: To deduce whether similar or distinct populations of vestibular afferents are activated by acoustic and galvanic vestibular stimulation by comparing the effectiveness of 'matched' stimuli in eliciting vestibulospinal reflexes.

Methods: Twelve subjects (5 men, 7 women) underwent individual 'matching' of 2 ms tone burst and galvanic stimuli, using vestibulocollic reflexes so that corrected reflex amplitudes to tone burst and galvanic stimuli were within 10% of each other. These same intensities were then administered using 20 ms durations to determine whether they were equally effective in evoking vestibulospinal responses.

Movement-related potentials associated with self-paced, cued and imagined arm movements.

Self-paced movements, movement to a cue and imagined movement have all been reported to be preceded by a prolonged negativity on averaged electroencephalograph (EEG) recordings. Considerable evidence supports an important contribution from the supplementary motor area (SMA) to this potential and all three types of movement have been shown to be associated with SMA activation. This study was designed to compare the premovement component of these movement-related potentials (MRPs) in a group of subjects who performed each of these three types of movement.