| SYSTEMS RECONSOLIDATION: THE EXISTENCE OF MULTIPLE
RETROGRADE AMNESIC GRADIENTS. |
| J. Debiec1; J.E. LeDoux1*;
K. Nader2 |
| 1. Center for Neural Science, New York University, New
York, NY, USA |
| 2. Department of Psychology, McGill University, Montreal,
PQ, Canada |
|
Lesion studies suggest a time-limited role
for the hippocampus in the acquisition of conditioned contextual fear
memories. Typically, the length of the retrograde amnesic (RA) gradient
is in the order of weeks. Recently, we found that reactivation of
temporally remote and hippocampally independent contextual fear memories
rendered the memories hippocampal dependent again. Here we asked how
long the reactivated remote memory depends on the hippocampus again
(systems reconsolidation). Rats were placed in a chamber and given
8, 1mA, 1 sec shocks. They were returned to the training context 45
days later for 90 sec to reactivate the memory. Following reactivation
animals received sham or electrolytic lesions of the hippocampus 4,
24 or 48 hours later. Lesioned rats demonstrated impaired freezing
only when the surgery was done 4 or 24 hours, but not 48, hours after
reactivation. Repeated weekly testing of the 4 hr group did not show
any spontaneous recovery for 5 weeks. Whereas the length of the retrograde
gradient for new information is weeks (1st RA gradient), the remote
reactivated memory depends on the hippocampus only for 2 days (2nd
RA gradient). To test whether a trace can undergo a 3rd round of systems
reconsolidation, another group of rats were treated identically as
the 48 hr group in the last experiment, except immediately prior to
surgery they had a reactivation session. Again lesioned rats showed
a deficit. These data are the first to describe a complete 2nd RA
gradient and to demonstrate the existence of a 3rd gradient.
Supported by: Grants MH: 46516, 38774, 00956, 58911 to JL and VW
I/77 376, HSFP RGP0094/2001-B to KN and JL.
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