FORNIX LESIONS CAN FACILITATE ACQUISITION OF THE TRANSVERSE PATTERNING TASK - A CHALLENGE FOR CONFIGURAL THEORIES OF HIPPOCAMPAL FUNCTION

Configural theories of hippocampal function predict that hippocampal d ysfunction should impair acquisition of the transverse patterning task , which involves the concurrent solution of three discrimination probl ems: A+ versus B-; B+ versus C-; and C+ versus A-. The present study t ested this prediction in rats using computer-graphic stimuli presented on a touch-screen. Experiment 1 assessed the effects of fornix lesion s when the three problems were introduced sequentially (phase 1: A+ vs B-; phase 2: A+ vs B-, B+ vs C-: phase 3: A+ vs B-, B+ vs C-, C+ vs A -). Fornix lesions significantly facilitated acquisition of the comple te transverse patterning task (phase 3) but had no effect on the numbe r of sessions or errors required to attain criterion during phase 1 or phase 2, In experiment 2, in which all three problems were presented concurrently from the outset of training, fornix-lesioned animals outp erformed control animals during the seventh block of acquisition trial s and were not impaired during any stage of acquisition, Importantly, these same animals were significantly impaired on two allocentric spat ial tasks: T-maze alternation (experiments 1 and 2) and the Morris Swi m Task (experiment 1). These results contradict the predictions of con figural theories of hippocampal function and cast doubt on the popular notion that spatial learning is a special case of configural learning .