Dissociation of endogenous components of auditory evoked potentials following carbachol microinjection into the cholinoceptive pontine inhibitory area

Abstract

Microinjections of the cholinergic agonist, carbachol, into an area ventromedial to the principal nucleus of the locus coeruleus produce pronounced suppression of postural somatomotor and sympathetic visceromotor functions, and profound unresponsiveness to external stimuli. In order to clarify whether this unresponsiveness is due exclusively to disruption of motor components of various behavioral responses, we examined changes in the endogenous components of auditory evoked potentials recorded in conjunction with a tone discrimination task. Concomitant with carbachol-induced behavioral unresponsiveness, the late positive component (LPC) at 250–350 ms disappeared, while the early positive component at 80–150 ms was enhanced. This result suggests that, after the onset of carbachol-induced behavioral unresponsiveness, external stimuli enter the brain but are not integrated in neural processes reflected in LPC which has previously been implicated in processes mediating orienting responses, selective attention, and/or cognitive evaluation.