Gamma frequencies coordinate theta oscillations in the hippocampus via cross-frequency coupling

- By: Santiago Canals
- Affiliation: Instituto de Neurociencias CSIC-UMH Alicante
- Date: 2018-05-03T14:30:00+00:00
Cross-frequency coupling (CFC), has been measured in multiple regions during perception, attention and memory formation. It is believed that CFC plays a role in the coordination of local computations and communication, yet the mechanisms underlying this coordination are largely unknown. In the hippocampus, it has been shown that information transmission between the CA1 and its afferent regions in CA3 and the entorhinal cortex (EC) is organized in separated gamma frequency channels that are synchronized by the phase of the slower CA1 theta rhythm. However, recent findings challenge the role of gamma frequencies as substrate for information routing. Here we propose an alternative functional role for these gamma activities: the coordination of theta rhythm generators in the hippocampus. We used multichannel recordings in freely exploring animals to analyze theta and gamma oscillations in hippocampus. We find dynamic theta oscillations with periods of phase-locked waves alternating with periods of theta asynchrony. Moreover, we find that CFC between theta and gamma is stronger between oscillations originated in the same layer. Theta synchronization and CFC are higher when the animal explores novel stimuli during a learning task. Systematic analysis of cross-frequency directionality showed that the amplitude of gamma oscillations consistently drives the phase of theta waves in all layer-specific theta-gamma pairs.