Journal of Neuroscience, Vol 10, 1472-1478, Copyright © 1990 by Society for Neuroscience
Learning and behavioral-long-term potentiation: importance of controlling for motor activity
EL Hargreaves, DP Cain and CH Vanderwolf
Department of Psychology, University of Western Ontario, London, Canada.
A series of brief, high-frequency trains of electrical stimulation
delivered to the perforant-path results in long-term potentiation (LTP) of
the dentate gyrus as measured by average evoked potentials (EPs). Similar
increases in dentate evoked potentials have been reported after natural
learning. Previous studies of this behavioral LTP have not adequately
controlled for ongoing behavior at the time of recording, even though motor
activity also influences the amplitude of EPs. Chronically implanted rats
were trained in both a radial-arm maze and an avoidance task using a
crossover design. EPs in the dentate gyrus following perforant-path
stimulation were recorded daily under 3 different behavioral conditions:
immobility, movement, and freely behaving. After completion of both tasks,
animals were given tetanizing stimulation of the perforant path. Results
indicated strong improvements in the performance of both tasks.
Tetanization induced significant LTP, which was still present at the end of
5 d. Significant differences were found between EPs collected during
immobility and movement throughout the experiment. No evidence of
behavioral LTP was observed, and the EPs remained consistent with baseline
measures. These data show the necessity of controlling for ongoing behavior
at the time of recording in electrophysiological studies of learning. The
data also indicate that the phenomenon of behavioral LTP, as assessed by
hippocampal EPs, is not universal to all learning experiences.
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