• The single switch paradigm produced a significant dose-dependent impairment in memory encoding for task rules demonstrated by decreased overall accuracy in the post-switch session. • In awake behaving rats we observed local field potentials that showed high activity in the theta band frequency (4-10 Hz). • The overall power of the theta rhythm was reduced in a dose-dependent manner. • In the encoding phase of the task when waveform averages were gated to the light onset, we found clear and consistent synchrony across the EC, DG, and ACC. • There were significant differences in the pre- stimulus vs. post-stimulus waveform, potentially indicating an encoding-stimulus evoked enhancement of the overall theta rhythm. • In the retrieval phase of the task when waveform averages were gated to the onset of the tone, we found preliminary evidence indicating that synchronization between the DG and the ACC increases preferentially during retrieval events. EFFECTS OF ACUTE ETHANOL ON MEMORY ENCODING, RETRIEVAL, AND THE THETA RHYTHM K.S. Edwards, J.N. Gaines, D. Task, B. Givens Department of Psychology, The Ohio State University, Columbus, OH 43210 469.12/FF2 Overview of Operant Task Representative Histology Effects of Ethanol on Within-Session Accuracy Hypothesized MemoryCircuit INTRODUCTION METHODS REFERENCES & ACKNOWLEDGMENTS SUMMARY Experimental Timeline • Subjects: Adult male Long-Evans rats • Operant Task Rule Contingencies: • Delayed match to sample (DMTS) • Delayed non-match to sample (DNMTS) • Rules were counterbalanced • Performance Criterion before switch: • >70% accuracy for 3 sessions • Single Rule Switch • Day 1: Pre-Switch = Rule A • Day 2: Injection 10 min pre-switch=Rule B • Day 3: Post Switch = Rule B • Electrode Construction and Implantation • Recording Wires: stainless steel coated with Teflon (3 microns diameter) • Implanted into three sites: • Anterior Cingulate • Dentate Gyrus • Entorhinal Cortex • Intraperitoneal Ethanol Injections (10 min pre switch): • 0.0, 0.25, 0.50, 0.75, or 1.0 g/kg ethanol (10% w/v) • Physiology Recording and Analysis • Spike 2 Software (CED) • Filtered for theta range (5-12 Hz) Acute exposure to low doses of ethanol (EtOH) affects many cognitive functions including memory (White et al, 2000). The purpose of this study was to adapt a well- validated (Dudchenko, 2004) model of episodic-like memory into a serial rule switching paradigm to assess the effects of EtOH on memory encoding and retrieval for specific task rules while performing simultaneous in vivo recordings of the ongoing theta rhythm in the entorhinal cortex (EC), dentate gyrus of the hippocampus (DG), and anterior cingulate cortex (ACC). The theta rhythm in these regions has been implicated in both the encoding and the retrieval of memories (Hasselmo et al, 2002). We hypothesized that EtOH would disrupt memory encoding more so than retrieval, measured by impaired accuracy in the post-switch session. Furthermore, we hypothesized that disruption of theta rhythm synchrony between the anatomical regions would correlate with this memory impairment. Dudchenko, P. A. (2004). An overview of the tasks used to test working memory in rodents. Neuroscience and Biobehavioral Reviews, 24, 699-709. Hasselmo, M.E., Bodelón, C., Wyble, B.P. (2002). A proposed function for hippocampal theta rhythm: Separate phases of encoding and retrieval enhance reveral of prior learning. Neural Computation, 14, 793-817 White, A. M., Matthews, D. B., & Best, P. J. (2000). Ethanol, memory, and hippocampal function: A review of recent findings. Hippocampus, 10, 88-93. We would like to acknowledge the assistance of R. Mills, B. Morgan, and J.D. Tucker. This research was supported by NIAAA grant 1 R03 AA018214-01A1 Synchronization of mean waveform Averages by dose around light onset (Encoding) and tone onset (Retrieval) by recording location (Anterior Cingulate, Dentate Gyrus, Entorhinal Cortex) Dose-Dependent effects on area under power spectrum curve in theta-band frequency Area Under Power Curve mV