Familiarity-modulated synapses model cortical microcircuit novelty responses

Since environments are constantly in flux, the brain’s ability to identify novel stimuli that fall outside its own internal representation of the world is crucial for an organism’s survival. Within the mammalian neocortex, inhibitory microcircuits are proposed to regulate activity in an experience-dependent manner and different inhibitory subtypes exhibit distinct novelty responses. Discerning the function of diverse neural circuits and their modulation by experience can be daunting unless one has a biologically plausible novelty mechanism that is both understandable and flexible. Here we introduce a simple novelty mechanism, familiarity modulated synapses (FMSs), which exhibit synaptic changes following exposure to a stimulus via unsupervised, local modulations. FMSs stand apart from other familiarity mechanisms in their simplicity: they require no separated training and testing phases, no specialized connectomics, and can distinguish novelty without relying on slow recurrent convergence. Implementing FMSs within a model of a cortical microcircuit that includes multiple inhibitory subtypes, we simultaneously reproduce three distinct novelty effects recently observed in experimental data from visual cortical circuits in mice. This includes oddball and omission responses as well as novelty effects that occur over drastically different time scales. The model demonstrates how experimentally-observed microcircuit structure give rise to qualitatively distinct novelty responses across the various cell populations. Altogether, our findings highlight the flexibility of FMSs and opens the door to computationally and theoretically investigating how distinct synapse modulations can lead to a variety novelty responses in a simple, understandable, and biologically plausible setup.