J. E. LEDOUX, N. HARANHALLI, L. W. MASSIE, J. P. LITTLE, *L. R. JOHNSON;
Ctr Neural Sci, NYU, New York, NY.

How memory is organized within neural networks is a fundamental question in neuroscience. We used Pavlovian fear conditioning to study the discrete organization patterns of neurons activated in an associative memory paradigm. In Pavlovian fear conditioning a neutral stimulus, such as an auditory tone, is temporally paired with an aversive unconditioned stimulus (US), such as a foot shock. The previously neutral stimulus becomes a conditioned stimulus (CS) capable of eliciting defensive responses. Given that the lateral amygdala (LA) is a locus for the storage of memories created through Pavlovian fear conditioning and that individual neurons within LA store aspects of the associative fear memory, we asked whether these neurons are organized in a specific manner and whether a patterned organization maybe present across different animals storing the same memory? Rats were habituated and subject to either 5 paired or unpaired presentations of the CS (20sec, 5kHz, 75db tone) and US (0.5sec, 1.0mA foot shock). Animals were then studied behaviorally or anatomically. In the behavioral study rats that received paired training exhibited significantly higher levels of conditioned fear (freezing) to the CS in a novel context. In the anatomical study, exactly 60mins following training (Schafe et al, 2000), brains were prepared for immunocytochemical detection of phosphorylated mitogen activated kinase (pMAPK). pMAPK activated neurons were mapped and quantified using Neurolucida (Microbrightfield, VT). Specific regions of the LA showed greater pMAPK activation. This suggests associatively activated neurons are discretely localized to regions of the nucleus. We next asked if matching constellations of activated neurons could be found across paired animals. We found examples of common constellations in paired animals and in contrast control animals shared fewer matching neurons. We hypothesize that those neurons that are activated in both paired and unpaired animals represent common aspects of the training experience, such as the context and the US, while the neurons unique to the paired animals are representative of the associative aspects of the stored memory. We conclude that associative memory formation in LA involves systematic constellations of neurons.
Support Contributed By: R01MH046516;P50MH058911;K05MH067048;R37MH38774

Program No. 370.8/KK26
Poster presentation:Monday, Oct 16, 2006, 11:00 AM -12:00 PM
Location: Georgia World Congress Center: Halls B3-B5