Abstract
Abstract The effects of two types of weak visual stimuli (short and long trains of light flashes perceived binocularly) on alpha motoneuron response were investigated in a phasic stretch reflex in normal human subjects. These types of visual stimuli affect the frequency and amplitude of mesencephalic reticular neurons of intact cats in predictable ways. The reticular formation has connections with fusimotor neurons which can be readily and quickly activated along the pyramidal tract. Since fusimotor discharge has a powerful effect on alpha motor activity by biasing spindle sensitivity, it may be assumed that the arousal and attenuation characteristics of reticular neurons to visual stimulation will be reflected in alpha motoneuron response. Experimental results from five adults (three females, two males) showed that brief presentation of the intermittent visual stimuli increased both the variance and the mean amplitude of the muscle action potential whilst continued presentation reduced these measures at least to control level. The findings indicate that fusimotor activity may be determined by use of surface EMG, provided proper control is exercised over variables which affect the reflex response.
Published Version
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