A local circuit approach to understanding integration of long-range inputs in primary visual cortex

Abstract

Integration of inputs by cortical neurons provides the basis for the complex information processing performed in the cerebral cortex. Here, we have examined how primary visual cortical neurons integrate classical and nonclassical receptive field inputs. The effect of nonclassical receptive field stimuli and, correspondingly, of long-range intracortical inputs is known to be context-dependent: the same long-range stimulus can either facilitate or suppress responses, depending on the level of local activation. By constructing a large-scale model of primary visual cortex, we demonstrate that this effect can be understood in terms of the local cortical circuitry. Each receptive field position contributes both excitatory and inhibitory inputs; however, the inhibitory inputs have greater influence when overall receptive field drive is greater. This mechanism also explains contrast-dependent modulations within the classical receptive field, which similarly switch between excitatory and inhibitory. In order to simplify analysis and to explain the fundamental mechanisms of the model, self-contained modules that capture nonlinear local circuit interactions are constructed. This work supports the notion that receptive field integration is the result of local processing within small groups of neurons rather than in single neurons.

Functional MRI reveals spatially specific attentional modulation in human primary visual cortex

“…More integrated models, in which responses depend on strong influences other than the bottom-up thalamic inputs, are required (e.g., ref. 44). The results of this study also help to bolster conjectures that perceptual learning occurs within V1 (e.g., refs.…”

Recruitment of Local Inhibitory Networks by Horizontal Connections in Layer 2/3 of Ferret Visual Cortex

“…Although this seems paradoxical, such opposing effects can be explained by local circuit integration yielding emergent inhibition. Our experimental results suggest that high contrast stimuli may evoke emergent inhibition yielding suppression, while low contrast stimuli may fail to recruit inhibitory networks and yield facilitation, consistent with a previous model (Somers et al 1998).…”

“…Thus convergent horizontal connections, which generate purely excitatory events when stimulated individually, may evoke inhibition when stimulated in combination. This idea is supported by evidence that excitation and inhibition are inseparable (Douglas and Martin 1991;Somers et al 1995Somers et al , 1998.…”

Delayed maturation of receptive field center/surround mechanisms in V2

“…monkeys, the details of the circuits underlying center͞surround responses of V1 neurons are currently in dispute (15)(16)(17)(18)(19)(20)(21)(22). A general consensus view is that the center responses of V1 neurons reflect the neural activity of feedforward connections and neighboring local neurons, whereas surround responses are mediated by the intrinsic long-range connections and͞or the feedback connections from extrastriate visual areas.…”