Woodry, R. | Search bioRxiv

bioRxiv2025

Memory responses in visual cortex track recall success after single-trial encoding

Episodic memory retrieval is thought to rely on the reactivation of prior perceptual representations in sensory cortex, a phenomenon known as cortical reinstatement. Support for this idea in early sensory areas comes from memory studies involving repeated exposure and explicit recall instructions. In everyday life, however, people rely on details from single events without repeated practice or instruction. We used fMRI to test whether memory responses emerge in early visual cortex after a single encoding event. Twenty adults viewed objects presented once in one of four parafoveal locations, then later completed object recognition (old/new) and location recall tasks in which objects were shown foveally. Both memory tasks evoked spatially tuned, albeit substantially lower amplitude, responses compared to encoding in V1 to V3. These responses were tuned to the encoded parafoveal location, even though the recognition task did not ask the participant to remember the encoded location. These responses were more robust and precise for successfully remembered items, linking neural tuning in early visual cortex to one-shot memory performance. Our findings demonstrate that early visual cortex supports the defining property of episodic memory, the ability to retrieve sensory details from a single event. Significance StatementEpisodic memory allows us to vividly recall details from single past experiences. While it is hypothesized that this "mental time travel" relies on reactivating sensory cortex, previous studies used highly practiced associations or explicit visualization cues, which differ from how we naturally recall unique events. In this fMRI study, participants viewed a stream of unique objects at parafoveal locations. We found that later retrieval of these objects spontaneously reactivated early visual cortex in a spatially specific manner even when spatial location was not probed: The memory reactivated the same retinotopic location where the object initially appeared. Furthermore, the precision of this reactivation predicted memory success. These findings demonstrate that sensory cortex is fundamental to the rapid, one-shot learning that characterizes human episodic memory.

neuroscience↗

bioRxiv2024

Feedback scales the spatial tuning of cortical responses during visual memory

Perception, working memory, and long-term memory each evoke neural responses in visual cortex. While previous neuroimaging research on the role of visual cortex in memory has largely emphasized similarities between perception and memory, we hypothesized that responses in visual cortex would differ depending on the origins of the inputs. Using fMRI, we quantified spatial tuning in visual cortex while participants (both sexes) viewed, maintained in working memory, or retrieved from long-term memory a peripheral target. In each condition, BOLD responses were spatially tuned and aligned with the targets polar angle in all measured visual field maps including V1. As expected given the increasing sizes of receptive fields, polar angle tuning during perception increased in width up the visual hierarchy from V1 to V2, V3, hV4, and beyond. In stark contrast, the tuned responses were broad across the visual hierarchy during long-term memory (replicating a prior result) and during working memory. This pattern is consistent with the idea that mnemonic responses in V1 stem from top-down sources, even when the stimulus was recently viewed and is held in working memory. Moreover, in long-term memory, trial-to-trial biases in these tuned responses (clockwise or counterclockwise of target), predicted matched biases in memory, suggesting that the reinstated cortical responses influence memory guided behavior. We conclude that feedback widens spatial tuning in visual cortex during memory, where earlier visual maps inherit broader tuning from later maps thereby impacting the precision of memory. Significance StatementWe demonstrate that remembering a visual stimulus evokes responses in visual cortex that differ in spatial extent compared to seeing the same stimulus. Perception evokes tuned responses in early visual areas that increase in size up the visual hierarchy. Prior work showed that feedback inputs associated with long-term memory originate from later visual areas with larger receptive fields resulting in uniformly wide spatial tuning even in primary visual cortex. We replicate these results and show that the same pattern holds when maintaining in working memory a recently viewed stimulus. That trial-to-trial difficulty is reflected in the accuracy and precision of these representations suggests that visual cortex is flexibly used for processing visuospatial information, regardless of where that information originates.

neuroscience↗