Theta rhythm oscillations and sequence encoding in the hippocampus

Phasic changes in variables including membrane depolarization and synaptic input may set appropriate dynamics for encoding and retrieval during each cycle of the hippocampal theta rhythm. Modeling demonstrates that phasic changes allow activation of an appropriate subset of interconnected neurons, resulting in better encoding of sequences in sparse networks. During retrieval, phasic changes in membrane depolarization allow sampling across a range of retrieval strengths, preventing insufficient or excessive retrieval activity. The phasic transition between dynamics dominated by entorhinal input and dynamics dominated by excitatory synapses arising in region CA3 prevents retrieval from interfering with encoding of new input from entorhinal cortex.