Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2004 Apr 6;101(14):5064-8.
doi: 10.1073/pnas.0308528101. Epub 2004 Mar 29.

Visual Memory Task for Rats Reveals an Essential Role for Hippocampus and Perirhinal Cortex

Affiliations
Free PMC article

Visual Memory Task for Rats Reveals an Essential Role for Hippocampus and Perirhinal Cortex

G T Prusky et al. Proc Natl Acad Sci U S A. .
Free PMC article

Abstract

Visual recognition memory is subserved by a distributed set of neural circuits, which include structures of the temporal lobe. Conflicting experimental results regarding the role of the hippocampus in nonspatial forms of such memories have been attributed to species, task, and lesion discrepancies. We have overcome obstacles that have prevented a direct evaluation of the role of the hippocampus in this type of memory by developing for rats a nonspatial, picture-based, trial-unique, delayed matching-to-sample task that is a procedural analogue of standard visual recognition memory tasks used in primates. With this task, we demonstrate that rats have a visual memory profile, which is analogous to that in primates and depends on the function of perirhinal cortex. We also find that selective lesions of hippocampus impair delay-dependent visual memory with a profile different from that produced by damage to the perirhinal cortex. These data demonstrate that rats have a visual recognition memory system fundamentally similar to primates that depends on the function of the hippocampus.

Figures

Fig. 1.
Fig. 1.
Visual water task configured for MTS. (Left) Sample pool. (Right) Choice pool. (Upper) Top view. (Lower) Front view. Sample pool: A sample picture (+) was displayed on a computer monitor that faced into the wide end of a trapezoidal-shaped tank containing water. A platform was hidden under the surface of the water directly below the monitor, and a faux divider was situated 46 cm from the front wall of the tank. Choice pool: The sample image (+) and a novel image (-) were each displayed on monitors facing into the end of a trapezoidal-shaped pool. A 46-cm divider extended into the pool from the front wall of the tank and a platform was hidden under the surface of the water directly below the sample picture.
Fig. 2.
Fig. 2.
MTS performance of intact rats and control tests. (A) MTS accuracy of rats decreased gradually as the delay between the sample and choice phase was increased. Performance of >80% accuracy was maintained with delays up to 2 min. Performance fell with longer delays, but was still above chance at a delay of 16 min. Random performance was seen at a 120-min delay. ±SEMs are smaller than the data point symbols. (B) Probe test. The accuracy of animals during a choice phase with a 1-min delay was 82% when the hidden platform was placed under the sample picture on (Probe +). Accuracy in choosing the sample picture fell to 10% when the hidden platform was placed under the novel picture (Probe -). (C) Long-term stability in delay performance; average choice accuracy with 1-min delay before and after trials completed with 120-min delay. Animals performed with high accuracy (81%) when 1-min delay was tested the first time (Pre1 min), and performance fell to chance (50%) with a 120-min delay was implemented (2 h). When 1-min delay performance was retested on the next day (Post1 min), performance returned to Pre1 min levels (86%).
Fig. 3.
Fig. 3.
Outline of perirhinal cortex and hippocampal lesions. (A) Reconstruction of perirhinal lesions in six animals. Brains were sectioned, stained, and photographed, and the lesions were reconstructed. Three coronal planes of section through perirhinal cortex (from bregma -3.8 mm, -5.3, and -6.72 mm) were chosen for presentation (23) and the reconstructions were superimposed (gray) on line drawings modified from Burwell (24). The size of the lesions varied, with some lesions encroaching on lateral portions of entorhinal cortex and temporal neocortex. All rats, however, sustained bilateral damage to the perirhinal cortex, and none of the lesions involved the hippocampus. (B) Reconstruction of hippocampal lesions in four animals. Brains of animals that sustained hippocampal injections of N-methyl-d-aspartate were sectioned, stained, and photographed, and the lesions were reconstructed. Three coronal planes of section through hippocampus are presented (from bregma -3.8 mm, -5.3, and -6.72 mm) for each animal in the form of line drawings modified from Burwell (24). The extent of hippocampal damage varied (gray), but all lesions covered >75% loss of the principal subfields. In no animal did evidence occur of the lesion encroaching into subicular or entorhinal cortices.
Fig. 4.
Fig. 4.
Effect of sham surgery, perirhinal cortex removal, and hippocampal lesions on delay-dependent MTS performance. (A) The performance of sham-lesioned animals (n = 5) before (filled circles) and after (open circles) surgery did not differ. (B) Bilateral perirhinal cortex damage dramatically decreased DMTS performance (open squares) compared with prelesion values (filled squares) at all delays except the longest, 16 min. (C) Hippocampal lesions (open diamonds) significantly reduced MTS performance at all delays, compared with prelesion values from the same animals (filled squares). (D) Perirhinal cortex lesions (open squares) resulted in significantly worse performance at delays of 30 sec, 1 min, and 2 min, than did hippocampal lesions (filled diamonds). *, P < 0.05; ±SEMs, which were smaller than the data point symbols.

Similar articles

See all similar articles

Cited by 33 articles

See all "Cited by" articles

Publication types

Feedback