Khoury, C. F. | Search bioRxiv

bioRxiv2024

Wider spread of excitatory neuron influence in association cortex than sensory cortex

The basic structure of local cortical circuits, including the composition of cell types, is highly conserved across the cortical processing hierarchy. However, computational roles and the spatial and temporal properties of population activity differ fundamentally in sensory-level and association-level areas. In primary sensory cortex, the timescale of population activity is shorter and pairwise correlations decay more rapidly over distance between neurons, supporting a population code that is suited to encoding rapidly fluctuating sensory stimuli. In association cortex, the timescale of population activity is longer, and pairwise correlations are stronger over wider distances, a code that is suited to holding information in memory and driving behavior. Here, we tested whether these differences in population codes could potentially be explained by intrinsic differences in local network structure. We targeted single excitatory neurons optogenetically, while monitoring the surrounding ongoing population activity in sensory (auditory cortex) and association (posterior parietal cortex) areas in mice. While the temporal impacts of these perturbations were similar across regions, the spatial spread of excitatory influence was wider in association cortex than in sensory cortex. Our findings suggest that differences in recurrent connectivity could contribute to the different properties of population codes in sensory and association cortex, and imply that circuit models of cortical function should be tailored to the properties specific to individual regions. Significance statementCell-type-specific functional interactions and connectivity patterns have largely been studied in sensory cortex. Yet the properties of local network activity differ dramatically across the cortical hierarchy, possibly due to differences in intrinsic connectivity patterns. Here, we compared the functional impacts of individual excitatory neurons on local population activity, finding differences in the spatial spread of excitatory influence across regions. Our findings suggest that the structure of local networks differs across the cortical processing hierarchy, and these differences should be considered in circuit models of processes such as decision-making and working memory.

neuroscience↗

bioRxiv2022

Specialization in somatostatin subnetworks in sensory and association cortex

Arousal powerfully influences cortical activity, in part by modulating local inhibitory circuits. Somatostatin-expressing inhibitory interneurons (SOM) are particularly well-situated to shape local population activity in response to shifts in arousal, yet the relationship between arousal state and SOM activity has not been characterized outside of sensory cortex. To determine whether SOM activity is similarly modulated by behavioral state across different levels of the cortical processing hierarchy, we compared the behavioral modulation of SOM neurons in auditory cortex (AC), a primary sensory region, and posterior parietal cortex (PPC), an association-level region of cortex. Behavioral state modulated activity differently in AC and PPC. In PPC, transitions to high arousal were accompanied by large increases in activity across the full PPC neural population, especially in SOM neurons. In AC, arousal transitions led to more subtle changes in overall activity, as individual SOM and Non-SOM neurons could be either positively or negatively modulated during transitions to high arousal states. The coding of sensory information in population activity was enhanced during periods of high arousal in AC, but not PPC. Our findings suggest unique relationships between activity in local circuits and arousal across cortex, which may be tailored to the roles of specific cortical regions in sensory processing or the control of behavior. Significance statementThe effects of arousal on brain networks are profound, but vary across regions. Somatostatin neurons may carry out some of the effects of arousal on local network activity in sensory cortex, by modulating response gain and decorrelating population activity. However, SOM neurons have not been well studied outside of sensory cortex, and so it is unknown whether SOM neurons are similarly affected by shifts in brain state throughout the cortex. Here, we have revealed specialization in the relationship between arousal and activity in SOM neurons that could contribute to the diversity of arousal-related impacts on local computation across cortical regions.

neuroscience↗