NUNEZ, ANTONIO ALBERTO.

Rats with bilateral, electrolytic, dorsal-hippocampal lesions
were compared with operated controls in a straight runway to assess
the effects of the lesion on the animals' reactions to food-incentive
shifts. Within each surgical group, half the animals received 40
preshift trials with low reward while the other half received the same
number of trials with high reward, following this all Ss were shifted
to the opposite reward magnitude and received 40 additional trials.
At this point, the Ss were shifted back to original reward magnitudes
for another 40 trials. Finally, all Ss underwent experimental
extinction. The data failed to support the hypothesis that dorsal
hippocampal rats "overreact" to incentive shifts. Lesion animals, as
compared to controls, were less sensitive to the reward shifts and
showed more resistance to extinction. The results suggest that the
lesion produces a deficit in the Ss ability to vary behavior specially
on tasks that require response decrements. However, the lesion-produced
hyperactivity introduced confounding aspects to this interpretation.