Hippocampal area CA1 and remote memory in rats - PubMed (original) (raw)
Hippocampal area CA1 and remote memory in rats
Amber C Ocampo et al. Learn Mem. 2017.
Abstract
Hippocampal lesions often produce temporally graded retrograde amnesia (TGRA), whereby recent memory is impaired more than remote memory. This finding has provided support for the process of systems consolidation. However, temporally graded memory impairment has not been observed with the watermaze task, and the findings have been inconsistent with context fear conditioning. One possibility is that large hippocampal lesions indirectly disrupt (by retrograde degeneration) the function of areas that project to the hippocampus that are important for task performance or thought to be important for storing consolidated memories. We developed a discrete lesion targeting area CA1, the sole output of the hippocampus to neocortex, and tested the effects of this lesion on recent and remote memory in the watermaze task, in context fear conditioning, and in trace fear conditioning. In all three tasks, recent and remote memory were similarly impaired after CA1 lesions. We discuss factors that help to illuminate these findings and consider their relevance to systems consolidation.
© 2017 Ocampo et al.; Published by Cold Spring Harbor Laboratory Press.
Figures
Figure 1.
Lesions targeted both dorsal and ventral regions of CA1. Photomicrographs of six coronal histological sections through the hippocampus of a representative (A) sham brain and (B) a brain with a CA1 lesion. The sections are arranged from anterior (top) to posterior (bottom). Arrows indicate the CA1 borders in each section for the sham animal.
Figure 2.
Lesions encompassed the majority of area CA1, while leaving the rest of the hippocampus largely intact. The black bars show the mean percent damage to the CA1 subregion of the hippocampus for animals in the recent condition (top, n = 16) and remote condition (bottom, n = 16). Extra-CA1 damage is shown in white.
Figure 3.
Spatial memory retention in the watermaze was impaired following CA1 lesions in both the recent and remote conditions. (A) Test probe performance measured as the mean percent time spent in the target quadrant. The dashed line indicates chance performance (25%). (B) Test probe performance measured as the mean percent time spent in the platform location. The dashed line indicates chance performance (4%). Performance after CA1 lesions is shown in black (recent n = 16, remote n = 16). Sham performance is shown in white (recent n = 16, remote n = 16). Error bars indicate SEM; sham scores are well above chance, P < 0.0001; (*) P < 0.005.
Figure 4.
Context and trace fear memory were impaired following CA1 lesions in both the recent and remote conditions. (A) Context fear retention measured as mean percent freezing during the 8-min context test. (B) Trace fear retention during the tone test measured as mean percent freezing during the 240 sec after the onset of the tone. Performance after CA1 lesions is shown in black (recent n = 16, remote n = 16). Sham performance is shown in white (recent n = 16, remote n = 16). Error bars indicate SEM; (*) P < 0.0001.
References
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- Anagnostaras SG, Gale GD, Fanselow MS. 2002. The hippocampus and Pavlovian fear conditioning: reply to Bast et al. Hippocampus 12: 561–565. -PubMed
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- Bolhuis JJ, Stewart CA, Forrest EM. 1994. Retrograde amnesia and memory reactivation in rats with ibotenate lesions to the hippocampus or subiculum. Q J Exp Psychol B 47: 129–150. -PubMed
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