SEPTAL-LESIONS IMPAIR THE ACQUISITION OF A CUED PLACE NAVIGATION TASK- ATTENTIONAL OR MEMORY DEFICIT

These experiments were designed to analyze how medial septal lesions r educing the cholinergic innervation in the hippocampus might affect pl ace learning. Rats with quisqualic lesions of the medial septal area ( MS) were trained in a water maze and on a homing table where the escap e position was located at a spatially fixed position and further indic ated by a salient cue suspended above it. The lesioned rats were signi ficantly impaired in reaching the cued escape platform during training . In addition rats, did not show any discrimination of the training se ctor during a probe trial in which no platform or cue was present. Thi s impairment remained significant during further training in the absen ce of the cue. When the cued escape platform was located at an unpredi ctable spatial location, the MS-lesioned rats showed no deficit and sp ent more time under the cue than control rats during the probe trial. On the homing board, with a salient object in close proximity to the e scape hole, the MS rats showed no deficit in escape latencies, althoug h a significant reduction in spatial memory was observed. However, thi s was overcome by additional training in the absence of the cue. Under these conditions, rats with septal lesions were prone to develop a pu re guidance strategy, whereas normal rats combined a guidance strategy with a memory of the escape position relative to more distant landmar ks. The presence of a salient cue appeared to decrease attention to en vironmental landmarks, thus reducing spatial memory. These data confir m the general hypothesis that MS lesions reduce the capacity to rely o n a representation of the relation between several landmarks with diff erent salience. (C) 1998 Academic Press.