John Farley¹ (), Ziam Khan², Alexander Ksendzovsky², Sara Inati⁴, Yaoda Xu³, Kareem Zaghloul⁴, Weizhen Xie^1,2,4; ¹Department of Psychology, University of Maryland, College Park, ²Department of Neurosurgery, University of Maryland, Baltimore, ³Department of Psychology, Yale University, ⁴Surgical Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health

The ability to maintain visual short-term/working memory (STM/WM) for goal-directed behavior is often attributed to delay-period activity in neocortical regions, such as the prefrontal cortex (PFC). However, recent evidence implicates the medial temporal lobe (MTL), traditionally associated with long-term memory, in visual WM. This raises the question of whether the PFC and MTL redundantly represent WM content or serve distinct roles. One possibility is that the PFC retains task-relevant stimulus information, including task structure and prior knowledge shared across individuals, while the MTL captures idiosyncratic, context-specific aspects of the encoded stimuli. Alternatively, both regions may represent the same WM content, communicated through coupled neuronal activity during retention, as suggested in recent studies. To test these possibilities, we recorded intracranial EEG from the PFC and MTL in seven participants performing a delay-match-to-sample task. Participants viewed a single object from one of eight categories (e.g., cats, cars) for 200 ms, followed by a 1300-ms delay, and judged whether a test object drawing from the same category matched the encoded object. Decoding analyses revealed object category information in both regions during the delay. However, representational geometry analyses uncovered striking differences: whereas PFC representations were remarkably consistent across individuals, MTL representations exhibited high variability. Using the same stimuli, prior fMRI research demonstrated that WM representations during delay aligned across sensory and posterior parietal cortices. The PFC representations revealed by intracranial EEG here aligned closely with those found in fMRI, whereas MTL representations showed weaker correspondence. These findings highlight complementary roles for the PFC and MTL in supporting visual WM: While the PFC provides stable representations that generalize across observers and regions, the MTL encodes more flexible, observer-specific representations. Combined, these mechanisms integrate shared and unique aspects of stimulus information, enabling robust WM for adaptive goal-directed behavior.

Acknowledgements: Y.X. is supported by NIH grant R01EY030854; W.X. is supported by NIH grant R00NS126492