Excitation creates a distributed pattern of cortical suppression due to varied recurrent input.

Dense local, recurrent connections are a major feature of cortical circuits, yet how they affect neurons' responses has been unclear, with some studies reporting weak recurrent effects, some reporting amplification, and others indicating local suppression. Here, we show that optogenetic input to mouse V1 excitatory neurons generates salt-and-pepper patterns of both excitation and suppression. Responses in individual neurons are not strongly predicted by that neuron's direct input. A balanced-state network model reconciles a set of diverse observations: the observed dynamics, suppressed responses, decoupling of input and output, and long tail of excited responses. The model shows recurrent excitatory-excitatory connections are strong and also variable across neurons. Together, these results demonstrate that excitatory recurrent connections can have major effects on cortical computations by shaping and changing neurons' responses to input.

Performance in even a simple perceptual task depends on mouse secondary visual areas.

Primary visual cortex (V1) in the mouse projects to numerous brain areas, including several secondary visual areas, frontal cortex, and basal ganglia. While it has been demonstrated that optogenetic silencing of V1 strongly impairs visually guided behavior, it is not known which downstream areas are required for visual behaviors. Here we trained mice to perform a contrast-increment change detection task, for which substantial stimulus information is present in V1. Optogenetic silencing of visual responses in secondary visual areas revealed that their activity is required for even this simple visual task. In vivo electrophysiology showed that, although inhibiting secondary visual areas could produce some feedback effects in V1, the principal effect was profound suppression at the location of the optogenetic light. The results show that pathways through secondary visual areas are necessary for even simple visual behaviors.

Inhibition stabilization is a widespread property of cortical networks.

Many cortical network models use recurrent coupling strong enough to require inhibition for stabilization. Yet it has been experimentally unclear whether inhibition-stabilized network (ISN) models describe cortical function well across areas and states. Here, we test several ISN predictions, including the counterintuitive (paradoxical) suppression of inhibitory firing in response to optogenetic inhibitory stimulation. We find clear evidence for ISN operation in mouse visual, somatosensory, and motor cortex. Simple two-population ISN models describe the data well and let us quantify coupling strength. Although some models predict a non-ISN to ISN transition with increasingly strong sensory stimuli, we find ISN effects without sensory stimulation and even during light anesthesia. Additionally, average paradoxical effects result only with transgenic, not viral, opsin expression in parvalbumin (PV)-positive neurons; theory and expression data show this is consistent with ISN operation. Taken together, these results show strong coupling and inhibition stabilization are common features of the cortex.

The rat medial frontal cortex controls pace, but not breakpoint, in a progressive ratio licking task.

The medial frontal cortex (MFC) is crucial for selecting actions and evaluating their outcomes. Outcome monitoring may be triggered by rostral parts of the MFC, which contain neurons that are modulated by reward consumption and are necessary for the expression of relative reward value. Here, we examined if the MFC further has a role in the control of instrumental licking. We used a progressive ratio licking task in which rats had to make increasing numbers of licks to receive liquid sucrose rewards. We determined what measures of progressive ratio performance are sensitive to value by testing rats with rewards containing 0%-16% sucrose. We found some measures (breakpoint, number of licking bouts) were sensitive to sucrose concentration and others (response rate, duration of licking bouts) were not. Then, we examined the effects of reversibly inactivating rostral (medial orbital) and caudal (prelimbic) parts of the MFC. We were surprised to find that inactivation had no effects on measures associated with value (e.g., breakpoint). Instead, inactivation altered behavioral measures associated with the pace of task performance (response rate and time to break). These effects depended on where inactivations were made. Response rates increased and time to break decreased when the caudal prelimbic area was inactivated. By contrast, response rates decreased and the time to break increased when the rostral medial orbital cortex was inactivated. Our findings suggest that the medial frontal cortex has a role in maintaining task engagement, but not in the motivational control of action, in the progressive ratio licking task. (PsycINFO Database Record (c) 2019 APA, all rights reserved).