Lesions of the entorhinal cortex impair acquisition of hippocampal-dependent trace conditioning.
Rabbits with the electrolytic lesions of bilateral entorhinal cortex (EC) were trained with the hippocampal-dependent trace conditioning of the nictitating membrane response. The multiple-unit activity of the hippocampal CA1 region was recorded during conditioning. The conditioned stimulus was a tone (1 kHz, 85 dB, 200-ms duration), the unconditioned stimulus was a corneal air puff (3 psi, 150-ms duration), and the interstimulus interval was 750 ms. The EC-lesioned animals showed only 30% conditioned response (CR) by the ninth session while the sham-operated animals showed above 80% CR. The lesioned animals did not show learning-related changes in the hippocampal activity. When the training was switched to the 300-ms interstimulus interval trace conditioning, both groups learned above 80% CR. The EC-lesioned animals, however, showed less learning-related activity in the hippocampus than the sham-operated animals. These results suggest that the development of the learning-related activity in the hippocampus depends on the intact EC, and that the EC may provide a possible pathway conveying learning information from the cerebellum or cerebral cortex to the hippocampus during the trace conditioning.
Ryou
J W
JW
Department of Psychology, Korea University, Seoul, 136-701, Korea. jwryou@u.arizona.edu
Cho
S Y
SY
Kim
H T
HT
D000818:Animals; D001931:Brain Mapping; D003214:Conditioning, Classical / Q000502:physiology*; D003215:Conditioning, Eyelid / Q000502:physiology; D018728:Entorhinal Cortex / Q000502:physiology*; D006624:Hippocampus / Q000502:physiology*; D011939:Mental Recall / Q000502:physiology*; D019580:Perforant Pathway / Q000502:physiology; D011817:Rabbits