Dynamic Axis-Tuned Cells in the Monkey Lateral Prefrontal Cortex during a Path-Planning Task

The lateral prefrontal cortex (lPFC) plays a crucial role in the cognitive processes known as executive functions, which are necessary for the planning of goal-directed behavior in complex and constantly changing environments. To adapt to such environments, the lPFC must use its neuronal resources in a flexible manner. To investigate the mechanism by which lPFC neurons code directional information flexibly, the present study explored the tuning properties and time development of lPFC neurons in male Japanese monkeys during a path-planning task, which required them to move a cursor to a final goal in a stepwise manner within a checkerboard-like maze. We identified "axis-tuned" cells that preferred two opposing directions of immediate goals (i.e., vertical and horizontal directions). Among them, a considerable number of these axis-tuned cells dynamically transformed from vector tuning to a single final-goal direction. We also found that the activities of axis-tuned cells, especially pyramidal neurons, were also modulated by the abstract sequence patterns that the animals were to execute. These findings suggest that the axis-tuned cells change what they code (the type of behavioral goal) as well as how they code (their tuning shapes) so that the lPFC can represent a large number of possible actions or sequences with limited neuronal resources. The dynamic axis-tuned cells must reflect the flexible coding of behaviorally relevant information at the single neuron level by the lPFC to adapt to uncertain environments.SIGNIFICANCE STATEMENT The lateral PFC (lPFC) plays a crucial role in the planning of goal-directed behavior in uncertain environments. To adapt to such situations, the lPFC must flexibly encode behaviorally relevant information. Here, we investigated the goal-tuning properties of neuronal firing in the monkey lPFC during a path-planning task. We identified axis-tuned cells that preferred "up-down" or "left-right" immediate goals, and found that many were dynamically transformed from vector tuning to a final-goal direction. The activities of neurons, especially pyramidal neurons, were also modulated by the abstract sequence patterns. Our findings suggest that PFC neurons can alter not only what they code (behavioral goal) but also how they code (tuning shape) when coping with unpredictable environments with limited neuronal resources.