Anterograde amnesia and temporally graded retrograde amnesia for a nonspatial memory task after lesions of hippocampus and subiculum

Abstract

We studied the importance of the hippocampus and subiculum for anterograde and retrograde memory in the rat using social transmission of food preference, a nonspatial memory task. Experiment 1 asked how long an acquired food preference could be remembered. In experiment 2, we determined the anterograde amnesic effects of large lesions of the hippocampus that included the subiculum. In experiment 3, large lesions of the hippocampus that included the subiculum were made 1, 10, or 30 d after learning to determine the nature and extent of retrograde amnesia. Normal rats exhibited memory of the acquired food preference for at least 3 months after learning. Hippocampal lesions that included the subiculum produced marked anterograde amnesia and a 1-30 d temporally graded retrograde amnesia. The results show the importance of the hippocampus and related structures for nonspatial memory and also demonstrate the temporary role of these structures in long-term memory.

Fig. 1.

A, The influence of strength of training on percent preference for the familiar food across delays.White bars indicate performance of groups given a 10 min interaction with demonstrator rats, striped barsindicate performance of groups given a 30 min interaction with demonstrator rats, and black bars indicate performance of groups given 30 min interactions with different demonstrator rats on 3 consecutive days. B, The influence of strength of training when the delays were combined. C, Percentage of preference for the familiar food across delays (strength of training combined at each delay). Error bars show SEM.

Fig. 2.

Reconstructions of coronal sections showing the largest (striped) and smallest (black) lesions in rats with ibotenic acid lesions. Each series of sections progresses (left to right) from anterior to posterior levels. Numbers represent the distance in millimeters posterior to bregma.

Fig. 3.

Percent preference for the familiar food for control (n = 16) animals and H-IBO (n = 15) animals. Training occurred after the lesions were made, and retention was tested 48 hr later. The control group performed above chance and scored higher than the H-IBO group. The H-IBO group did not perform above chance. *p < 0.05, significant difference between the two groups. Error bars show SEM.

Fig. 4.

Reconstructions of coronal sections showing the largest (striped) and smallest (black) lesion in rats with radiofrequency lesions. Each series of sections progresses (left to right) from anterior to posterior levels. Numbers represent the distance in millimeters posterior to bregma.

Fig. 5.

Percent preference for the familiar food for control animals (CON) and H-RF animals across three training–surgical intervals. For the 1 d condition, the control group performed significantly better than the H-RF group. The H-RF groups did not perform above chance in the 1 and 10 d conditions. In the 30 d condition, the two groups performed similarly, and both groups performed well above chance. *p < 0.05, significant difference between the control and H-RF groups. Error bars show SEM.