Rats with kainate-colchicine hippocampal lesions (HL) and controls (C) were
initially trained in the Morris water maze with procedures that deterred t
heir prepotent thigmotaxic response. Training began with an escape platform
that occupied nearly the entire pool. The area to which the rats could esc
ape was made smaller by substituting smaller platforms as training progress
ed. In contrast to standard procedures, HL rats and C rats showed comparabl
e performance during acquisition and preferentially searched the goal quadr
ant on probe trials during which the platform was removed. In a follow-up e
xperiment, the platform was moved to a random position along the wall, whic
h required a switch to a thigmotaxic response far most effective escape. HL
rats that were thigmotaxic before place training did not switch to a thigm
otaxic response as readily as did controls, behavior consistent with the vi
ew that hippocampal damage reduces pliancy.