Hippocampectomy disrupts trace eye-blink conditioning in rabbits.
The role of the hippocampus (HPC) in trace eye-blink conditioning was evaluated using a 100-ms tone conditioned stimulus (CS), a 300- or 500-ms trace interval, and a 150-ms air puff unconditioned stimulus (UCS). Rabbits received complete hippocampectomy (dorsal & ventral), sham lesions, or neocortical lesions. Hippocampectomy produced differential effects in relation to the trace interval used. With a 300-ms trace interval, HPC-lesioned Ss showed profound resistance to extinction after acquisition. With a 500-ms trace interval, HPC-lesioned Ss did not learn the task (only 22% conditioned responses (CRs) after 25 sessions, whereas controls showed greater than 80% after 10 sessions), and on the few trials in which a CR occurred, most were "nonadaptive" short-latency CRs (i.e., they started during or just after the CS and always terminated prior to UCS onset). The authors conclude that the HPC encodes a temporal relationship between CS and UCS, and when the trace interval is long enough (e.g., 500 ms), that the HPC is necessary for associative learning of the conditioned eye-blink response.
Moyer
J R
JR
Department of Cell, Molecular, and Structural Biology, Northwestern University Medical School, Chicago, Illinois 60611.
Deyo
R A
RA
Disterhoft
J F
JF
D000818:Animals; D001245:Association Learning / Q000502:physiology*; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology; D003215:Conditioning, Eyelid / Q000502:physiology*; D004292:Dominance, Cerebral / Q000502:physiology; D005108:Extinction, Psychological / Q000502:physiology; D006624:Hippocampus / Q000502:physiology*; D007858:Learning / Q000502:physiology*; D008297:Male; D011939:Mental Recall / Q000502:physiology; D009474:Neurons / Q000502:physiology; D011817:Rabbits; D011930:Reaction Time / Q000502:physiology