STIMULUS SEPARATION IN ENSEMBLES OF MUSCLE AFFERENTS

A new method was used for analysis of ensemble coding in populations of receptor afferents. The aim was to investigate ensemble coding in populations of primary muscle spindle afferents (MSAs) and to assess the role of the fusimotor system for the encoding ability of these ensembles. Secondly, to investigate ensemble coding in mixed populations of different muscle afferents, and to compare the capacity of mixed populations with populations of only one type of afferent. Thirdly we studied the effects of muscle fatigue on the stimulus separation in ensembles of primary MSAs. The results show that ensembles of primary MSAs discriminated better between muscle stretches than individual MSAs. Mixed ensembles of afferents discriminated better between muscle stretches than ensembles of only one type of afferent. The increase in separation with increasing ensemble size was considerably reduced after cutting the ventral roots or induction of muscle fatigue in heteronymous muscles, signifying the importance of an intact fusimotor drive for stimulus separation in ensembles of primary MSAs.