Journal of Neurophysiology, Vol 54, Issue 5 1194-1212, Copyright © 1985 by APS

ARTICLES

Effects of single intracortical microstimuli in motor cortex on activity of identified forearm motor units in behaving monkeys

S. S. Palmer and E. E. Fetz

We examined the magnitude and extent of output effects elicited from focal cortical sites on the activity of individual motor units (MUs) by delivering single-pulse intracortical microstimuli (S-ICMS) (5-15 microA) during isometric wrist activity. Stimulation sites in the precentral gyrus (area 4) were chosen for study if stimulus-triggered averages (stimulus-TAs) of multiunit electromyograms (EMGs) revealed poststimulus facilitation (PStimF) of EMG activity in any of the coactivated wrist muscles. Single MUs were then isolated in the facilitated muscles with a remotely controlled tripolar microelectrode. MUs were identified by their signatures in their parent muscles (from MU-triggered averages of EMGs) and by their firing pattern during ramp-and-hold wrist responses. One objective was to quantify the magnitude and time course of the effects on single MUs by compiling peristimulus histograms of MU firing. The cross-correlation histograms between S-ICMS and MU action potentials showed peaks with onset latencies of 8.8 +/- 1.7 ms (mean +/- SD, n = 64) and durations of 1.8 +/- 1.2 ms (n = 104). The cumulative sums of the correlogram peaks resembled the rising phase of corticomotoneuronal excitatory postsynaptic potentials previously recorded in forelimb motoneurons. Comparison of correlogram peaks with stimulus-TAs of MU potentials suggests that the duration of PStimF of multiunit EMG can be accounted for, in approximately equal proportions, by l) the variation in firing time of single MUs (i.e., the width of the MU correlogram peaks), 2) the width of single MU potentials, and 3) the contribution of different MUs at different latencies. The sizes of the correlogram peaks relative to base line were larger than the PStimF of multiunit EMGs, and increased more rapidly with stimulus intensity, indicating appreciable cancellation in the multiunit records. A second objective was to determine whether S-ICMS affected all the MUs of a facilitated muscle, or only a particular subset. Of 104 MUs sampled in facilitated muscles, 99 (95%) were found to be individually facilitated (P less than 0.05). MU firing patterns during isometric ramp-and-hold torque responses were characterized as phasic, phasic-tonic, tonic, or decrementing; stimulation at a given cortical site was found to facilitate all four types of MUs. When more than one muscle showed PStimF from a site, MUs belonging to each of the facilitated muscles were facilitated individually by S-ICMS at that site.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				M. Rivlin-Etzion, O. Marmor, G. Saban, B. Rosin, S. N. Haber, E. Vaadia, Y. Prut, and H. Bergman Low-Pass Filter Properties of Basal Ganglia Cortical Muscle Loops in the Normal and MPTP Primate Model of Parkinsonism J. Neurosci., January 16, 2008; 28(3): 633 - 649. [Abstract] [Full Text] [PDF]

				A. G. Davidson, V. Chan, R. O'Dell, and M. H. Schieber Rapid Changes in Throughput from Single Motor Cortex Neurons to Muscle Activity Science, December 21, 2007; 318(5858): 1934 - 1937. [Abstract] [Full Text] [PDF]

				M. H. Schieber and G. Rivlis Partial Reconstruction of Muscle Activity From a Pruned Network of Diverse Motor Cortex Neurons J Neurophysiol, January 1, 2007; 97(1): 70 - 82. [Abstract] [Full Text] [PDF]

				S. N. Baker, M. Chiu, and E. E. Fetz Afferent Encoding of Central Oscillations in the Monkey Arm J Neurophysiol, June 1, 2006; 95(6): 3904 - 3910. [Abstract] [Full Text] [PDF]

				S. I. Perlmutter, M. A. Maier, and E. E. Fetz Activity of Spinal Interneurons and Their Effects on Forearm Muscles During Voluntary Wrist Movements in the Monkey J Neurophysiol, November 1, 1998; 80(5): 2475 - 2494. [Abstract] [Full Text] [PDF]

				A. Belhaj-Saif, J. H. Karrer, and P. D. Cheney Distribution and Characteristics of Poststimulus Effects in Proximal and Distal Forelimb Muscles From Red Nucleus in the Monkey J Neurophysiol, April 1, 1998; 79(4): 1777 - 1789. [Abstract] [Full Text] [PDF]