RUNNING HEAD: Encoding and retrieval in CA3 CONTACT INFORMATION:

Encoding and retrieval in CA3 1 Past research (Hasselmo et al. 2002) suggests that some funda-mental tasks are better accomplished if memories are encoded and recovered during dierent parts of the theta cycle. A model of the CA3 subeld of the hippocampus is presented, using biophysical rep-resentations of the major cell types including pyramidal cells and two types of interneurons. Inputs to the network come from the septum and the entorhinal cortex (directly and via the dentate gyrus). A mechanism for parsing the theta rhythm into two epochs is proposed and simulated: in the rst half, the strong, proximal input from the dentate to a subset of CA3 pyramidal cells and coincident, direct in-put from the entorhinal cortex to other pyramidal cells creates an environment for strengthening synapses between cells, thus encoding information. During the second half of theta, cueing signals from the entorhinal cortex, via the dentate, activate previously strengthened synapses, retrieving memories. Slow inhibitory neurons (O-LM cells) play a role in the disambiguation during retrieval. We compare and contrast our computational results with existing experimental data and other contemporary models