Electrophysiological and behavioral reactivity to photic stimuli following septal lesions and pharmacological treatments in rats.

Analysis of behavioral reactivity and cortical visual evoked response (VER) to photic stimulation revealed 2 patterns of lesion-induced changes. One pattern of VERs reflected a hypoarousal electrophysiological condition. This pattern, present initially under all conditions, could be simulated with administration of scopolamine. A second pattern of VERs developed gradually and appeared to reflect a hyperaroused electrophysiological condition. This pattern could be simulated with d-amphetamine. While both lesion-induced electrophysiological patterns were associated with augmented behavioral reactivity to flashes, the hyperarousal pattern related to more intense conditions of stimulation and more sustained behavioral reactivity. Scopolamine, as opposed to d-amphetamine, reproduced the heightened behavioral reactivity to the flashes. These results were interpreted in terms of a "hypoarousal hypothesis" of sensory hyperreactivity.