Optogenetic reduction of theta oscillations induces remapping of time cells without memory impairment

In a delayed alternation spatial working memory task, hippocampal time cells fire during specific moments of the delay period to form a sequential representation of the entire delay interval. The causal relationship between these sequences and working memory remains unclear. Similarly, hippocampal theta oscillations are thought to support working memory, primarily through the generation of time cell sequences. To causally examine these relationships, we optogenetically silence the medial septal GABAergic theta-generating circuit during the delay portion of a delayed spatial alternation task. With hippocampal theta oscillations substantially reduced, many time cells exhibit remapping, and new time cells are recruited. Despite partial remapping of time cell sequences, behavioral performance remains intact and trajectory-specific coding is preserved, suggesting that task-relevant information remains available under theta disruption.