PROJECT SUMMARY Advancing our understanding of the neural basis of human cognition is limited due to the rarity of intracranial recordings in humans, and the inherent inadequacy of animal models. Additionally, studying something as complex and flexible as executive function will likely require recording from hundreds of neurons simultaneously, a scenario not currently possible in humans with the existing recording technology. Here we propose to use a new probe, the Neuropixels probe, with 960 possible recording electrodes on a single shank, to study human executive function. Placing these Neuropixels probes in the dorsolateral prefrontal cortex during awake deep brain stimulation recordings, we will assess the neural population activity during an executive function task that employs feature selection, conflict processing, and decisions (Aims 1 and 2). Making use of the unique recording structure of the probe, with electrodes placed regularly along the shank, we will evaluate the local topography, expecting cortical layers to stratify neural responses to task-conditions (Aim 1). We will also evaluate the neural population response to task conditions, hypothesizing that the neural dimensions and geometry exhibit features that explain the flexibility so crucial to executive function (Aim 2). This study will establish the neural underpinnings of human executive function.