Abstract
Neurons in the primate lateral prefrontal cortex (LPFC) can uniquely maintain representations of remembered stimuli in the absence of sensory stimuli and regardless of distractors. This resilience to distraction and change in environment may be key to our ability to maintain WM signals in real-world situations. Traditional spatial WM tasks in primates require sustained fixation and use simplified stimuli. It remains unclear whether under conditions with higher ecological validity-- with changing visual scenes and unconstrained eye movements-- LPFC neurons robustly maintain the contents of WM.
Here we use a novel spatial WM task set in a virtual environment to demonstrate resilient encoding of WM signals in LPFC neurons. In this task, a target is presented in a virtual arena for three seconds. It then disappears, followed by a two second delay period. Movement in the environment is then enabled and animals must navigate to the target location using a joystick. Neural recordings from the LPFC (area 8A dorsal/ ventral) were performed in two male rhesus macaques using two 10x10 Utah arrays.
Both animals were able to perform this task proficiently. Within a population of 2584 single neurons, we show robust spatial tuning to target location during the delay period (ventral array: 41% of neurons; dorsal array: 56% of neurons). Neural populations and neural ensembles are shown to contain large amounts of information about target location during the delay period based on high degrees of decoding accuracy on a single trial basis (~50%, 11% chance). Information content of the neural population remained stable after eye movement as well as changes in visual scene and motor activity that occurred during virtual navigation. Results demonstrate the robustness of WM encoding within the primate prefrontal cortex in the presence of eye movements and 3D navigation that reflect naturalistic conditions.