Top-down control of multimodal sensitivity in the barn owl optic tectum.

We studied the effects of electrically microstimulating a gaze-control area in the owl's forebrain, the arcopallial gaze fields (AGFs), on the responsiveness of neurons in the optic tectum (OT) to visual and auditory stimuli. Microstimulation of the AGF enhanced the visual and auditory responsiveness and stimulus discriminability of OT neurons representing the same location in space as that represented at the microstimulation site in the AGF. At such OT sites, AGF microstimulation also sharpened auditory receptive fields and shifted them toward the location represented at the AGF stimulation site. At the same time, AGF microstimulation suppressed the responsiveness of OT neurons that represented visual or auditory stimuli at other locations in space. The top-down influences of this forebrain gaze-control area on sensory responsiveness in the owl OT are strikingly similar to the space-specific regulation of visual responsiveness in the monkey visual cortex produced by voluntary attention as well as by microstimulation of the frontal eye fields. This experimental approach provides a means for discovering mechanisms that underlie the top-down regulation of sensory responses.