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Description:
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Several lines of evidence suggest that initial acquisition of learned behavior
involves multiple memory systems . In particular , lesions of the hippocampus impair the
acquisition of cognitive or relational memory , but do not impair the acquisition of
stimulus -response habits . Extinction behavior also involves new learning , and therefore
it is possible that multiple forms of memory may also underlie extinction .
We examined this hypothesis by training rats in a task in which extinction
behavior could putatively be acquired by either a cognitive or habit memory system .
Adult male Long -Evans rats were initially trained to run in a straight alley maze for food
reward . Following training they were placed into one of two extinction conditions . In
one condition rats were allowed to run to an empty goal box (i .e . response extinction ) . In
a second condition rats were placed into an empty goal box without making a running
response (i .e . latent or non -response extinction ) . Prior to each daily session of extinction
training , rats received intra -hippocampal infusions of either the local anesthetic
bupivacaine (0 .75 % solution /0 .5 ul ) , or saline .
Rats receiving saline infusions displayed extinction behavior in both the response
and non -response conditions . In contrast , rats receiving intra -hippocampal infusions ofbupivacaine extinguished normally in the response condition , but did not display nonresponse
extinction . This latent extinction effect was enhanced by decreasing the amount
of time between the last extinction trial and the probe trial . Additionally , administering
extinction training and probe trials in different contexts did not appear to prevent latent
extinction , however large variability may be masking this effect . The new context
administered during extinction prevented latent extinction in some animals , but not
others . These findings suggest that , similar to initial acquisition , the learning that occurs
during extinction also involves multiple memory systems . Specifically , the hippocampus
may selectively mediate extinction under conditions in which new stimulus -response
learning is prevented . |