Glutamate Infused Posttraining into the Hippocampus or Caudate-Putamen Differentially Strengthens Place and Response Learning

• Published in: Proceedings of the National Academy of Sciences - PNAS 1999-10, Vol.96 (22), p.12881-12886
• Main Author: Packard, Mark G.
• Format: Article
• Language: English
• Subjects: Animal memory; Animal training; Animals; Behavior, Animal - drug effects; Behavior, Animal - physiology; Behavioral neuroscience; Biological Sciences; Brain; Experimentation; Glutamic Acid - administration & dosage; Glutamic Acid - pharmacology; Hippocampus; Hippocampus - physiology; Injections; Learning; Learning - drug effects; Learning - physiology; Male; Mazes; Memory; Neurology; Nonassociative learning; Putamen - physiology; Rats; Rats, Long-Evans; Training
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.96.22.12881

A cross-maze task that can be acquired through either place or response learning was used to examine the hypothesis that post-training 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 μ g/0.5 μ l) or intracaudate (2 μ g/0.5 μ l) injections of either glutamate or saline (0.5 μ l). 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.