Optogenetic control of the medial septal area leads to reliable pacing of theta oscillations in the medial prefrontal cortex but the endogenous ~4-5 Hz oscillations remained unaffected
The hippocampus (HpC) and medial prefrontal cortex (mPFC) are known to be crucial for working memory. Both of the two brain regions exhibit prominent theta oscillations (7-9 Hz) which coordinate neuronal activity between the HpC and mPFC in working memory. Hippocampal theta oscillations are generated and paced by GABAergic neurons in the medial septal area (MSA), and optical stimulation of the GABAergic septal neurons can be used to modulate hippocampal theta oscillations. In our study, we found that hippocampal and mPFC theta oscillations shifted to the stimulation frequency with optical stimulation in the MSA. In addition, the power of theta oscillations in mPFC and the coherence of the oscillations between the mPFC and HpC also increased at the stimulation frequency. However, we found that mPFC power and mPFC-HpC coherence of endogenous ~4-5 Hz oscillations remained unaffected by septal stimulation. We also examined the effects of MSA stimulation on performance of a figure-8 maze alternation task and no behavioral improvements or impairments were observed.