Abstract Body

Aims

Oscillatory brain activity reflects brain states associated with learning and memory. In the hippocampus, slow gamma (25-55 Hz) and fast gamma (60-100 Hz) oscillations are related to the encoding and retrieval of memories, respectively. Theta oscillations (4-12 Hz) are associated with information encoding. Interestingly, slow and fast gamma appear to be nested within different theta phases, and therefore, associated with its cycles. Although such interactions are likely to be related to mnemonic functions, the relationship between theta phase of gamma oscillations and memory demands remains unclear.

Methods

We recorded from the hippocampal CA1region while animals were learning an appetitive task in a T-maze over a three day period. We assessed the theta-phase preference of gamma oscillations in the starting zone, and the junction zone of the maze i.e. maze location where animals must choose a right or left turn.

Results

We found a ~180 degree shift in theta-phase preference of slow gamma when animals learned the task and evolved their performance from novice to skilled. This phase-shift occurred in the starting zone and not in the junction zone, suggesting that either a recall or a decision process took place at the starting zone.

Conclusions

Our findings support the idea of a double role of slow gamma oscillations in encoding and retrieval of memories which is dependent on the theta-phase at which it occurs.

Acknowledgements

This work was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) to D.M.-V. and S.C (SFB 1280/A04 & F01, project number: 316803389).