Underlying mechanism of hemodynamic and fMRI response to optogenetic stimulation of somatostatin neurons.

Motivation: SST neurons, 30% of cortical interneurons, are crucial in interpreting fMRI data and understanding neurovascular coupling within the cortex. Goal(s): In this study we want to investigate the the SST-induced hemodynamic response Approach: we used several methods such as neural recording, BOLD-fMRI, and optical intrinsic signaling (OIS) with pharmacological applications. Results: We observed SST neuron activation causing local neural inhibition, resulting in negative BOLD-fMRI at projection sites. Additionally, it triggered initial NO-induced fast vasodilation, followed by astrocyte-mediated slow vasodilation. Impact: BOLD-fMRI reflects neural activity changes, yet certain interneurons induce hemodynamic responses without altering neural activity. Studying SST-induced responses is vital for interpreting fMRI.