A Direct Circuit Between Auditory & Visual Cortices Explains Cross-Modal Memory Formation, Suppression

Article: Remembering Is Seeing
Source: Harvard Medical School
Published: March 8, 2022

Direct projections between the auditory cortex (AuC, red) 
and the primary visual cortex (V1, green)

Memory is traditionally thought of as being processed in higher-order regions of the brain. Yet, in the sensory areas of the brain, there is an undeniable interplay between both these higher-order cognitive regions and the receptor organs, such as the eyes and the ears, where information about the world is initially received. Why there is more feedback from the higher-order cognitive regions compared to the receptor organs in the formation of memory, or why there seems to be communication between the visual and auditory cortices before sending information to higher-order brain regions, is not fully understood. Researchers at HMS further explored this interaction—how and where they take place in the brain—to better understand how memory helps us make predictions about our world, and how memory (experience) alters our interpretation of sensory information. Specifically, the scientists used a mouse model and a virtual reality system to investigate the projection of axons between the auditory and visual cortices, which prior research had established exists in both humans and mice. They found that the auditory axons had both auditory and (retinotopically matched) visual responses to the primary visual cortex (V1), and the number of visually responsive axons increased as the mouse was trained to associate the auditory and visual cues. When an auditory cue was used to trigger a memory about a visual stimulus, the memory association with the auditory cue selectively suppressed neuronal response to the visual stimulus (that is, the circuit from the auditory cortex likely targets local inhibitory neurons) in V1, but only after conditioning. More broadly, this finding provides a mechanism to explain the suppression of sensory response after learned experience, and ultimately, the research helps to inform how memory affects conditions such as post-trauma stress disorder (PTSD) that results in part from the cognitive misinterpretation of sensory stimuli due to traumatic prior experience.

Visual responses of neurons inhibited (blue) compared to neurons excited (red) late in conditioning (bottom) to a visual stimulus (left) compared to control (right); inhibited neurons in V1 show increased response after conditioning to auditory input (bottom left, blue)

My rating of this study: ⭐⭐⭐

Garner AR and Keller GB. "A cortical circuit for audio-visual predictions." Nature Neuroscience.  25:98-105. 2 December 2021. https://doi.org/10.1038/s41593-021-00974-7