Study reveals visual cortex's causal role in generating visual responses in auditory cortex
Researchers used cortical cooling to reversibly inactivate higher-order visual areas in ferrets, demonstrating that these regions causally generate visual responses recorded in auditory cortex. The study found that roughly half of visually responsive auditory neurons lost their visual activity during cooling, while a small subset paradoxically gained or enhanced responses, revealing complex circuit-level interactions. These findings clarify how the brain integrates information across sensory modalities and challenge simple feedforward models of multisensory processing.
Using reversible cortical cooling in ferrets, researchers inactivated the posteromedial lateral suprasylvian cortex (PMLS) and adjacent area 21 — higher-order visual regions — to test their causal role in driving visual responses within auditory cortex. Visual, auditory, and audiovisual responses were recorded across all auditory fields and cortical depths, with visual responses most prominent in infragranular layers and the non-tonotopic secondary auditory cortex of the Anterior Ectosylvian Gyrus (AEG). Cooling produced robust, bidirectional, and stimulus-specific changes in firing rates: approximately 50% of visually responsive units showed reduced or abolished visual responses, confirming a direct functional contribution from PMLS/area 21. Unexpectedly, around 5% of units showed enhanced or newly emergent visual responses during inactivation, indicating that PMLS/area 21 normally suppresses or gates alternative visual pathways into auditory cortex. Counterintuitively, neurons in the AEG — the region most densely innervated by the cooled visual areas — were less frequently affected than those in the posterior ectosylvian gyrus (PEG), contradicting straightforward feedforward anatomical predictions. Together, the results indicate that higher visual cortex shapes cross-modal auditory processing through a combination of direct excitatory drive and broader network-level modulation, adding significant complexity to current models of multisensory integration.
What's missing
The study is conducted exclusively in ferrets, and it remains unclear how directly these findings generalize to primate or human multisensory processing. The cooling method inactivates a relatively broad cortical region, making it difficult to fully disentangle contributions of PMLS versus area 21 individually. The mechanisms underlying the paradoxical enhancement of visual responses in ~5% of units — and the identity of the alternative visual pathways revealed by cooling — are not yet characterized.
What different sources said
- bioRxivCenter
Cortical cooling reveals a role for visual cortex in generating visual responses in auditory cortex
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