EFFECTS OF UNILATERAL REMOVAL OF BASAL FOREBRAIN CHOLINERGIC NEURONS ON CUED TARGET DETECTION IN RATS

Corticopetal cholinergic neurons in the basal forebrain (BF) were remo ved unilaterally from rats by infusing the cholinergic immunotoxin 192 IgG-saporin into the substantia innominata. After 2 weeks, the rats w ith right-hemisphere infusions showed signs of visuospatial neglect fo r targets in the left visual field in a cued visual target detection t ask based upon human covert orienting procedures. No behavioral effect s were evident 4-6 weeks post-infusion. Ten to 22 weeks post-infusion all rats responded more quickly and less accurately to targets in the visual field contralateral to the infusion than to targets ipsilateral to the infusion; further, accuracy for contralateral targets decrease d with increasing time between trial initiation and target presentatio n (target delay), whereas accuracy for ipsilateral targets increased w ith target delay. Cues did not affect responding to targets in the con tralateral visual field more than to targets in the ipsilateral field. The changes in performance could not be attributed to sensory or mnem onic impairment or to response bias. The temporal characteristics of r esponse accuracy and latency suggest the competitive interaction of tw o time-dependent processes: an attentional process which relies upon c holinergic input from the BF, and a response preparation process which is normally inhibited by the attentional process. These results sugge st a role for corticopetal cholinergic pathways in maintaining attenti on to salient stimuli by inhibiting subcortical motor circuits. (C) 19 98 Elsevier Science B.V.