Journal of Neuroscience, Vol 4, 298-308, Copyright © 1984 by Society for Neuroscience
Effects of reaction time performance on single-unit activity in the central auditory pathway of the rhesus macaque
AF Ryan, JM Miller, BE Pfingst and GK Martin
The activity of single units at various locations in the central auditory
pathway of rhesus macaques was recorded during the monkeys' performance and
nonperformance in an auditory reaction time task. Evoked unit responses
during performance were compared with those observed during passive
delivery of identical stimuli. Single units were recorded from the cochlear
nucleus, superior olivary complex, lateral lemniscus, inferior colliculus,
medial geniculate nucleus, and auditory cortex. Significant effects of task
performance on unit discharge patterns were observed at all levels of the
central auditory pathway: Spontaneous discharge rates in the more
peripheral auditory nuclei tended to be higher during performance. Evoked
discharge that occurred relatively late during a stimulus presentation
(greater than 75 msec after stimulus onset) was increased during
performance, compared with the nonperformance condition, in nuclei above
the cochlear nucleus. The initial latency of evoked discharge was increased
during performance for subcortical nuclei but was decreased for units in
auditory cortex. These results suggest that the effects of performance may
be mediated by a tonic increase in the excitability of auditory units which
operates primarily at peripheral auditory stations, and a descending,
stimulus-evoked increase in excitability which primarily influences the
cells of higher auditory nuclei. At the cortical level, these changes lead
to increased signal-to-noise ratio of the evoked response during
performance in the auditory task.