Glutamate infused posttraining into the hippocampus or caudate-putamen differentially strengthens place and response learning.
A cross-maze task that can be acquired through either place or response learning was used to examine the hypothesis that posttraining neurochemical manipulation of the hippocampus or caudate-putamen can bias an animal toward the use of a specific memory system. Male Long-Evans rats received four trials per day for 7 days, a probe trial on day 8, further training on days 9-15, and an additional probe trial on day 16. Training occurred in a cross-maze task in which rats started from a consistent start-box (south), and obtained food from a consistent goal-arm (west). On days 4-6 of training, rats received posttraining intrahippocampal (1 microgram/0.5 microliter) or intracaudate (2 microgram/0.5 microliter) injections of either glutamate or saline (0.5 microliter). On days 8 and 16, a probe trial was given in which rats were placed in a novel start-box (north). Rats selecting the west goal-arm were designated "place" learners, and those selecting the east goal-arm were designated "response" learners. Saline-treated rats predominantly displayed place learning on day 8 and response learning on day 16, indicating a shift in control of learned behavior with extended training. Rats receiving intrahippocampal injections of glutamate predominantly displayed place learning on days 8 and 16, indicating that manipulation of the hippocampus produced a blockade of the shift to response learning. Rats receiving intracaudate injections of glutamate displayed response learning on days 8 and 16, indicating an accelerated shift to response learning. The findings suggest that posttraining intracerebral glutamate infusions can (i) modulate the distinct memory processes mediated by the hippocampus and caudate-putamen and (ii) bias the brain toward the use of a specific memory system to control learned behavior and thereby influence the timing of the switch from the use of cognitive memory to habit learning to guide behavior.
Packard
M G
MG
Department of Psychology, Yale University, New Haven, CT 06520, USA. Mark.Packard@yale.edu
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D018698:Glutamic Acid / Q000008:administration & dosage* / Q000494:pharmacology; D006624:Hippocampus / Q000502:physiology*; D007858:Learning / Q000187:drug effects / Q000502:physiology*; D008297:Male; D011699:Putamen / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans
D018698:Glutamic Acid