Engaging in an auditory task suppresses responses in auditory cortex.

Although systems that are involved in attentional selection have been studied extensively, much less is known about nonselective systems. To study these preparatory mechanisms, we compared activity in auditory cortex that was elicited by sounds while rats performed an auditory task ('engaged') with activity that was elicited by identical stimuli while subjects were awake but not performing a task ('passive'). We found that engagement suppressed responses, an effect that was opposite in sign to that elicited by selective attention. In the auditory thalamus, however, engagement enhanced spontaneous firing rates but did not affect evoked responses. These results indicate that neural activity in auditory cortex cannot be viewed simply as a limited resource that is allocated in greater measure as the state of the animal passes from somnolent to passively listening to engaged and attentive. Instead, the engaged condition possesses a characteristic and distinct neural signature in which sound-evoked responses are paradoxically suppressed.