Laminar Circuit Organization and Inhibitory Neuronal Control of Primary Visual Cortex

The primary visual cortex (V1) is considered as the first cortical stage for visual information processing and has been extensively studied as the classic cortical model system.  Despite the detailed knowledge of V1 cortical circuit organization from previous anatomical and physiological studies, functional connections and response dynamics in local and micro-cortical circuits have yet to be thoroughly interrogated at the level of single neurons.  Here we used optic based circuit mapping techniques to assess the dominant excitatory and inhibitory pathways across all layers in mouse V1 slices. Mapping experiments combining laser scanning photiostimulation (LSPS) with whole cell recordings and fast voltage-sensitive dye imaging (VSDI), revealed layer-specific topographic organization of excitatory and inhibitory synaptic inputs. Further examining how principle neurons in V1 integrate multiple coincident inputs, near-simultaneous photostimulation was delivered to multiple lamina and the resulting excitatory output was measured. Surprisingly, compared to single inputs, sequential interlaminar coincident stimuli in local V1 circuitry resulted in dramatically reduced excitation but enhanced inhibition to excitatory neurons. The underlying mechanism was found to be due to a non-linear increase in the activation of inhibitory cells types during interlaminar circuit interaction. Taken together, these data provide quantitative evaluations of local excitation and inhibition across V1 cortical layers and further unveil a novel form of circuit performance which may be attributable to the integration of visual information and improvement of spatiotemporal resolution.