Recognition memory for objects, place, and temporal order: a disconnection analysis of the role of the medial prefrontal cortex and perirhinal cortex

Abstract

Recognition memory requires judgments of the previous occurrence of stimuli made on the basis of the relative familiarity of individual objects, or by integrating information concerning objects and location, or by using recency information. The present study examined the role of the medial prefrontal cortex (mPFC) and perirhinal cortex (PRH) in these distinct recognition memory processes using a series of behavioral tests: a novel object preference task, an object-in-place task, and a temporal order memory task. Also, a disconnection procedure was used to test whether these regions form components of an integrated system for recognition memory. Male DA rats received bilateral lesions in the PRH or mPFC or unilateral lesions placed in both cortices in either the same (PRH-mPFC IPSI) or contralateral (PRH-mPFC CONTRA) hemispheres. A fifth group underwent sham surgery (SHAM). In the object-in-place and temporal order memory tasks, the PRH, mPFC, and PRH-mPFC CONTRA groups were significantly impaired. However, performance in the novel object preference task was only impaired in the PRH group. No group was impaired in the object location task. These results demonstrate that the mPFC and PRH are crucial for object-in-place associational and recency discriminations, whereas the PRH but not the mPFC is important for the discrimination of novel and familiar individual objects. Importantly, these results provide direct support for the hypothesis that to make discriminations based on associational or recency information, both cortical regions operate within an integrated neural network for recognition memory.

Figure 1.

Diagram of the four object recognition memory tasks. A, Novel object preference task. B, Temporal order task. C, Object-in-place task. D, Object location task.

Figure 2.

Diagrammatic reconstructions showing the cases with the largest (gray) and smallest (black) lesions in the mPFC (A) and PRH (B) groups. The numbers correspond to the approximate position relative to bregma (Swanson, 1998).

Figure 3.

Diagrammatic reconstructions showing the cases with the largest (gray) and smallest (black) lesions in the PRH–mPFC CONTRA group. The numbers correspond to the approximate position from bregma (Swanson, 1998).

Figure 4.

Diagrammatic reconstructions showing the cases with the largest (gray) and smallest (black) lesions in the PRH–mPFC IPSI group. The numbers correspond to the approximate position from bregma (Swanson, 1998).

Figure 5.

Performance of the five experimental groups in the novel object preference task tested with either a 5 min (A) or a 2 h (B) delay between the sample and test phases. Shown for each group is the mean (+SEM) discrimination ratio in the first minute of the test phase only. *p < 0.05.

Figure 6.

Performance of the five experimental groups in the novel object preference task tested with either a 5 min (A) or a 2 h (B) delay between the sample and test phases. Shown for each group is the mean (+SEM) discrimination ratio in the first 2 min of the test phase. *p < 0.05; **p < 0.01.

Figure 7.

Performance of the five experimental groups in the object location task. Shown for each group is the mean (+SEM) discrimination ratio.

Figure 8.

Performance of the five experimental groups in the temporal order memory task. Shown for each group is the mean (+SEM) discrimination ratio. *p < 0.05.

Figure 9.

Performance of the five experimental groups in the object-in-place task. Shown for each group is the mean (+SEM) discrimination ratio. *p < 0.05; **p < 0.01.