Classifying sensory patterns and their effects on locomotion and tremor.

Methods are described for analyzing the patterns of sensory activity in peripheral nerves during unrestrained behaviour. In locomotion, nerves supplying ankle extensors and flexors typically show two bursts of sensory activity per step cycle. Variations in sensory input may be important in modulating the ongoing oscillation. Altered sensory input may also change the phase of an ongoing oscillation (as in human essential tremor) or may only have a transient reflex effect (as in Parkinsonian tremor). Various types of interactions can be analyzed using a model of the peripheral neuromuscular system and its central connections. In general, the following categories are suggested for sensory actions on neural oscillations: (1) modulation of (a) the amplitude or (b) the frequency; (2) resetting (i.e., a maintained change in the timing of an oscillation without changes in frequency); (3) repatterning an oscillation (a) over several cycles (e.g., gait changes in locomotion) or (b) within a cycle or two (e.g., the stumble corrective reaction); and (4) gating an oscillation on or off.