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Weizhen Xie, John Wittig Jr, Sara Inati, Kareem Zaghloul; The causal role of the medial temporal lobe in visual working memory precision. Journal of Vision 2020;20(11):797. doi: https://doi.org/10.1167/jov.20.11.797.
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Patients with medial temporal lobe (MTL) lesions often exhibit poor retention of precise visual information in long-term memory. This deficit has been attributed to the MTL’s role in pattern separation, in that MTL damage compromises the separation of similar visual information and thus reduces visual memory fidelity. However, it remains a heated debate whether the MTL is also critical for short-term retention of precise information in visual working memory (VWM). This is because the MTL is traditionally considered only relevant for long-term memory. This study aims to identify the critical role of the MTL in VWM precision. Study 1 examined how direct electrical stimulation to the MTL versus the parietal cortex affected VWM performance in 6 epilepsy patients with intracranial electrodes placed for seizure monitoring. Electrical stimulation was applied during the delay period (1 second) of a VWM color recall task. We found that hippocampal stimulation selectively reduced VWM precision, introducing more variability in recall responses (n=2). In comparison, as an active control, parietal stimulation did not significantly impact VWM precision (n=4). Study 2 further examined whether surgical removal of the MTL affected VWM performance using a within-subject design. VWM quantity and quality were measured before and after 8 patients’ resection surgery for their epilepsy treatment. We found that MTL lesions (e.g., hippocampus and entorhinal cortex) markedly reduced VWM precision without affecting the quantity of remembered VWM items nor color perception (n=4). Furthermore, in 4 patients who had no MTL resection (1 insula, 1 temporal pole, and 2 no resection), we found little change in VWM measures or color perception. Together, this study provides converging evidence for the causal role of the MTL in VWM precision, which is dissociable from parietal mechanisms underlying VWM quantity. These novel findings are central to a better understanding of the nature of VWM limitations.
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