Components of the responses of a population of DSCT neurons determined from single-unit recordings

1. Impulse activity of single units belonging to the dorsal spinocerebella tract (DSCT) was recorded in response to electrical stimulation of peripheral muscle nerves at group I intensities. The responses for 187 units were determined using a spike train analysis technique that facilitates the comparison of poststimulus response time course across units (response probability function, RPF; 16). 2. The poststimulus changes in impulse activity were represented in the waveform of the RPF. Principal component analysis was used to determine the component waveforms that were common to the responses across units. The analysis showed that there were a few waveforms that dominated the majority of the responses (85% of the total variability was accounted for by five principal component waveforms). 3. A cluster analysis based on three principal component waveforms revealed seven major groups of responses according to the patterns of their poststimulus activity. These response types were composed of different combinations of short- or long-latency excitation and inhibition. The same clusters were formed regardless of response amplitude or the source of the stimulus. 4. The responses were characterized by three general features, revealed by the first three principal components. The primary feature was the sign of the response, either mostly excitatory or inhibitory. The second feature was a distinction between a short- (up to 15 ms) and long- (approximately 30 ms) latency to peak response, and the third feature was the appearance of two separate phases of opposite sign in some of the responses.(ABSTRACT TRUNCATED AT 250 WORDS)