NEUROPHYSIOLOGICAL METHODS FOR STUDIES OF THE MOTOR SYSTEM IN FREELY MOVING HUMAN-SUBJECTS

In this paper, the following experimental methods for studies of the m otor system in freely moving human subjects will be considered: (i) el iciting the H-reflex and understanding its use as a test response, (ii ) methods to measure reciprocal inhibition between antagonist muscles, (iii) methods to measure presynaptic inhibition of Ia-afferent termin als in the spinal cord, (iv) certain aspects of the interpretation of peri-stimulus time histograms (PSTH) of single motor unit discharge, a nd finally, (v) stimulation of the motor cortex and the measurement of response parameters that may reflect task dependent changes. Two clos ely related ideas bearing directly on these methods will be emphasized -the influence of the background level of motor activity on input-outp ut properties of the neural pathway investigated and the operating poi nt on the input-output curves at which the experimental variable is me asured. Finally, in the discussion a simple model that is easily under standable in geometric terms is presented to help predict and interpre t the outcome of these sorts of experiments. (C) 1997 Elsevier Science B.V.