CONDITIONAL LEARNING AND MEMORY IMPAIRMENTS FOLLOWING NEUROTOXIC LESION OF THE CA1 FIELD OF THE HIPPOCAMPUS

Monkeys with bilateral lesions of the CAI field of the hippocampus pro duced by the injection of neurotoxin diagonally along the length of th e hippocampus were found to have a severe impairment on the retention of a conditional task learnt prior to surgery and on the new acquisiti on of several types of this task. They were equally impaired on condit ional tasks that required a spatial response or an object choice in re sponse to either visual or spatial cues. They were not impaired on sim ple visual discrimination tasks, simple spatial discrimination tasks o r reversal learning of these tasks. This pattern of impairment resembl es that seen in the same species with neurotoxic lesions within the ve rtical limb of the diagonal band of Broca or transection of the fornix . Monkeys with subtotal lesions of the adjacent medial temporal area w ere not consistently impaired on any of these tasks. The results sugge st that hippocampal lesions produce anterograde and retrograde amnesia for information other than reward association.