Prefrontal cortex neurons encode ambient light intensity differentially across regions and layers

While light can affect emotional and cognitive processes of the medial prefrontal cortex (mPFC),
no light-encoding was hitherto identified in this region. Here, extracellular recordings in awake
mice revealed that over half of studied mPFC neurons showed photosensitivity, that was
diminished by chemogenetic inhibition of intrinsically photosensitive retinal ganglion cells
(ipRGCs), or of the upstream thalamic perihabenular nucleus (PHb). In 15% of mPFC
photosensitive neurons, firing rate changed monotonically along light-intensity steps and
gradients. These light-intensity-encoding neurons comprised four types, two enhancing and two
suppressing their firing rate with increased light intensity. These types were also identified in the
PHb, where they exhibited shorter latency and increased sensitivity. Light suppressed prelimbic
activity but boosted infralimbic activity, mirroring their contrasting roles in fear-conditioning,
drug-seeking, and anxiety. We posit that prefrontal photosensitivity represents a substrate of
light-susceptible, mPFC-mediated functions, which could by studied as a therapeutical target in
psychiatric and addiction disorders.