Rat prefrontal cortical neurons selectively code strategy switches.

Howard Eichenbaum

Howard Eichenbaum

Howard Eichenbaum

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Neuronal activity in the prelimbic (PL) and infralimbic (IL) regions of the prefrontal cortex signals switching between the use of hippocampus- and caudate-dependent behavioral strategies in rodents performing maze tasks. These findings confirm lesion studies that revealed the importance of prefrontal areas to strategy switching, and characterize how prefrontal neuronal ensembles signal strategy switching. Previous studies have shown that the prefrontal cortex is needed for switching strategies used to solve maze problems in rats {1,2}. Here, it was observed that neuronal activity in the rodent prefrontal cortex (PL and IL) signals a switch between the use of a hippocampus-dependent place strategy and the use of a caudate-dependent turn strategy in maze performance. PL and IL neurons coded task strategy rather than specific goals, rewards, or overt behaviors, such that their firing patterns changed when a new strategy was adopted, even if the two strategies are expressed in identical behavior, whereas the firing patterns were stable when the same strategy was expressed by different behaviors. These findings align with observations on prefrontal neuronal activity in primates, suggesting conservation of fundamental prefrontal functions across mammalian species.

Norman White

Norman White

Norman White

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This study extends our knowledge of the role of the prefrontal cortex (PFC) in determining the use of different strategies for controlling behavior in rats, based on different types of information acquired by different memory systems. In 1947, Blodgett & McCutchan {1} introduced an elegantly simple method for distinguishing between two different kinds of learning in rats. The apparatus is a maze in the shape of a cross. A rat is easily trained to run from the south arm of the maze to the east arm to obtain food. Two fundamentally different kinds of learning can underlie this acquired behavior: response learning (turn right) or place learning (use information about the location of the food with respect to environmental cues). The two can be distinguished by starting the rat from the north arm. If the rat's behavior is controlled by a learned response it will turn right, entering the west arm; if its behavior is controlled by place information the rat will turn left, entering the east arm. Using this method, Packard & McGaugh {2} showed that response and place learning are dependent on the dorsal striatum and the hippocampus, respectively; the two kinds of information are acquired independently by partially overlapping neural systems in which the two structures are situated. Both systems include PFC. In the present paper, Rich and Shapiro take the next step in this story by showing that PFC neurons participate in the process by which control of behavior switches back and forth between hippocampus-based place learning and dorsal striatum-based response learning; that is, between the response and place "strategies". Rats were trained on pairs of responses from the south and north arms. Taken together, each pair required the use of either the response strategy (make the same turn from both start arms) or the place strategy (go to the same place from both arms). PFC neurons were stable after the rat's performance stabilized on either pair type, but their firing pattern changed while the rat switched between the two pair types. Significantly, there was no change in PFC firing pattern during a switch to a different pair of the same type (e.g. a reversal).