Dn. Harper et al., THE EFFECT OF MEDIAL SEPTAL AND MAMMILLARY BODY LESIONS ON THE SERIALPOSITION CURVE IN RATS, Psychobiology, 21(2), 1993, pp. 130-138
The effect of medial septum and mammillary body radio-frequency lesion
s on memory for list items was examined in rats. Subjects were exposed
, one arm at a time, to a list of 7 arms presented in a 12-arm radial
maze and were then required to return to a list arm in the subsequent
test phase. Before surgery, rats in both groups displayed a serial pos
ition curve-that is, superior recognition for arms presented at the be
ginning of the list (primacy effect) and the end of the list (recency
effect) but not the middle of the list. Medial septal lesions had two
major effects on performance: accuracy at all serial positions was red
uced, but while the primacy effect disappeared, a recency effect was r
etained. Following lesions of the mammillary bodies, the primacy and t
he recency effects disappeared, but there was no significant reduction
in overall accuracy. The disruptive effect of both lesions on memory
performance was robust despite extended training after surgery and was
unaffected by increasing the exposure time to list arms during presen
tation. The memory impairment observed in rats following a medial sept
al lesion mimics the disruption in memory for list items that has been
observed in patients with mild Alzheimer's disease and with Korsakoff
's syndrome, two diseases that involve neuropathological changes in th
e medial septum.