Primary visual cortex is the earliest visual information processing centre in the brain cortex. Visual information is processed differently in visual cortex depending on the properties of the stimuli. The four million neurons of the mouse cortex are classified based on their morphology, biochemistry and physiological properties. Firstly, there are excitatory (or pyramidal neurons) and inhibitory cells (or interneurons). The inhibitory neurons are classified into three main classes: somatostatin (Sst), vasoactive intestinal peptide (Vip), and parvalbumin (Pvalb) expressing interneurons. The main objective of the EU-funded SENSMOD (Microcircuits for behavioral modulation of sensory cortex) project was to understand the distinctive functional properties of the interneurons – Sst, Vip and Pvalb in the mouse primary visual cortex. Visual responses are strongly modulated by context (for example by locomotion). Most of the visual cortex neurons display maximal response to stimuli of a finite spatial size, a phenomenon called size tuning. Researchers studied how different cell classes (Sst, Vip and Pvalb) modulate size tuning by locomotion (running). In previous studies, only single condition (stimulus size or locomotion) was registered with only a few neurons simultaneously recorded. The novelty of the current approach was that researchers recorded hundreds of neuronal responses to a combination of stimulus size and locomotion in the same experiment. Project findings indicated that functional interactions of excitatory and inhibitory neurons strongly depend on sensory and behavioural context. In particular, the data resolved apparent contradictions in the literature and suggested a new model of signal modulation. In the SENSMOD model, Vip and Sst neurons inhibit each other in a stimulus-dependent winner-take-all circuit, while modulating a sub-network of excitatory neurons that interact with Pvalb cells. The results are important as the cortical microcircuits in the brain have strong similarities across different cortical areas of all mammals. A prediction of the project model points out that abnormal behaviour of a specific cell class might lead to a distortion of size tuning. Interestingly, the results might shed light on mental disorders such as schizophrenia as size tuning is significantly reduced in schizophrenia patients.
Visual stimulation, locomotion, primary visual cortex, SENSMOD, behavioural