Sur, M. — Page 3 | Search bioRxiv

bioRxiv2017

Reliable sensory processing in mouse visual cortex through inhibitory interactions between Somatostatin and Parvalbumin interneurons

Cortical neurons often respond to identical sensory stimuli with large variability. However, under certain conditions, the same neurons can also respond highly reliably. The circuit mechanisms that contribute to this modulation, and their influence on behavior remains unknown. Here we used novel double transgenic mice, dual-wavelength calcium imaging and temporally selective optical perturbation to identify an inhibitory neural circuit in visual cortex that can modulate the reliability of pyramidal neurons to naturalistic visual stimuli. Our results, supported by computational models, suggest that somatostatin interneurons (SST-INs) increase pyramidal neuron reliability by suppressing parvalbumin interneurons (PV-INs) via the inhibitory SST[->]PV circuit. Using a novel movie classification task, we further show that, by reducing variability, activating SST-INs can improve the ability of mice to discriminate between ambiguous stimuli. Together, these findings reveal a novel role of the SST[->]PV circuit in modulating the fidelity of neural coding critical for visual perception.

neuroscience↗

bioRxiv2017

Task-Dependent Representations Of Stimulus And Choice In Mouse Parietal Cortex

The posterior parietal cortex (PPC) has been implicated in perceptual decisions, but whether its role is specific to sensory processing or sensorimotor transformation is not well understood. To distinguish these possibilities, we trained mice of either sex to perform a visual discrimination task and imaged the activity of PPC populations during both engaged behavior and passive viewing. Unlike neurons in primary visual cortex (V1), which responded robustly to stimuli in both conditions, most neurons in PPC responded exclusively during task engagement. However, PPC responses were heterogeneous, with a smaller subset of neurons exhibiting stimulus-driven, contrast-dependent responses in both conditions. Neurons in PPC also exhibit stronger modulation by noise correlations relative to V1, as illustrated by a generalized linear model that takes into account both task variables and between-neuron correlations. To test whether PPC responses primarily encoded the stimulus or the learned sensorimotor contingency, we imaged the same neurons before and after re-training mice on a reversed task contingency. Unlike V1 neurons, most PPC neurons exhibited a dramatic shift in selectivity after re-training and reflected the new sensorimotor contingency, while a smaller subset of neurons preserved their stimulus selectivity. Mouse PPC is therefore strongly task-dependent, contains heterogeneous populations sensitive to stimulus and choice, and may play an important role in the flexible transformation of sensory inputs into motor commands.\n\nSignificance StatementPerceptual decision making involves both processing of sensory information and mapping that information onto appropriate motor commands via learned sensorimotor associations. While visual cortex (V1) is known to be critical for sensory processing, it is unclear what circuits are involved in the process of sensorimotor transformation. While the mouse posterior parietal cortex (PPC) has been implicated in visual decisions, its specific role has been controversial. By imaging population activity while manipulating task engagement and sensorimotor contingencies, we demonstrate that PPC, unlike V1, is highly task-dependent, heterogeneous, and sensitive to the learned task demands. Our results suggest that PPC is more than a visual area, and may instead be involved in the flexible mapping of visual information onto appropriate motor actions.

neuroscience↗