Descending Projections from Extrastriate Visual Cortex Modulate Responses of Cells in Primary Auditory Cortex

Abstract

Primary sensory cortical responses are modulated by the presence or expectation of related sensory information in other modalities, but the sources of multimodal information and the cellular locus of this integration are unclear. We investigated the modulation of neural responses in the murine primary auditory cortical area Au1 by extrastriate visual cortex (V2). Projections from V2 to Au1 terminated in a classical descending/modulatory pattern, with highest density in layers 1, 2, 5, and 6. In brain slices, whole-cell recordings revealed long latency responses to stimulation in V2L that could modulate responses to subsequent white matter (WM) stimuli at latencies of 5-20 ms. Calcium responses imaged in Au1 cell populations showed that preceding WM with V2L stimulation modulated WM responses, with both summation and suppression observed. Modulation of WM responses was most evident for near-threshold WM stimuli. These data indicate that corticocortical projections from V2 contribute to multimodal integration in primary auditory cortex.

A mouse model of higher visual cortical function

“…Another consequence of the small size of the mouse brain is that some of the higher visual areas abut other primary sensory areas such as auditory (A1) and somatosensory (S1) cortex[37]. In fact, RL and A have robust projections to S1 while LI, P and POR project to A1[••43,56]. Conversely, the higher visual areas receive sensory input from these other modalities as well[57](N. Jikomes and MA, personal communication ), supporting multisensory integration at a comparatively early stage in cortical processing.…”

Intracortical Circuits in Thalamorecipient Layers of Auditory Cortex Refine after Visual Deprivation

“…A nonexclusive further possibility is that the observed changes reflect homeostatic adjustment of latent multisensory processing in A1. Because extrastriate visual cortex can alter A1 activity (Banks et al, 2011), decreased visual activity during DE could lead to a homeostatic rebalancing of auditory circuits. Although our experiments cannot distinguish between these mechanisms, the sum of our observations indicates changes in both excitatory and inhibitory connections consequent to DE in L4 as well as L2/3.…”

Where are multisensory signals combined for perceptual decision-making?

“…cooling, pharmacological inactivation, or micro-stimulation) (Figure 2b). In multisensory systems, this is particularly problematic as sensory pathways interconnect at cortical and subcortical levels [22][23][24][25]49,50]. For example, visual information in non-primary auditory cortex may originate from direct connections with visual cortex, from earlier interactions between primary auditory and visual cortices (or multisensory thalamus) that are subsequently inherited through the ascending auditory system, or from top-down feedback from higher brain regions.…”