1007 Working Memory is Supported by Ramping Evidence Accumulation in the Dorsolateral Prefrontal Cortex

INTRODUCTION: Working memory (WM) is a fundamental and ubiquitous cognitive process allowing for the temporary storage and manipulation of information necessary for complex cognitive tasks often localized to the dorsolateral prefrontal cortex (DLPFC) in animal studies and fMRI studies. Sequential sampling and evidence accumulation represent one theory of how the brain computes working memory but lacks rigorous empirical evidence in humans. METHODS: Ten phase-2 epilepsy participants with DLPFC intracranial coverage engaged in an N-back WM task over multiple sessions. Intracranial EEG was analyzed with custom burst analysis, demixed PCA, and cluster based permutation statistics. Hierarchical drift diffusion modeling (HDDM) was applied to the behavioral data. Functional and anatomic control areas of Frontal Eye Fields (FEF) and White Matter (WM) were used. Generalized linear mixed effects models were used to compare behavioral and neural data. RESULTS: We found strong evidence supporting evidence accumulation in LFP signals in the DLPFC. Our findings reveal that evidence accumulates primarily in the high gamma band, with the slope of these accumulating signals correlating with the difficulty of the working memory task (p < 0.0004). The 2D cluster analysis and gamma burst rate analyses further supported these findings, highlighting the DLPFC's role in integrating and processing information during working memory tasks. CONCLUSIONS: This study provides the first direct human evidence of the DLPFC's role in evidence accumulation during working memory-based decision-making. The strong correlation between the slope of gamma band activity and task difficulty underscores the importance of the DLPFC in processing and integrating information. These findings advance our understanding of the neural mechanisms underlying working memory and suggest new directions for investigating cognitive processes in complex decision-making tasks.