Contributions of distinct prefrontal neuron classes in reward processing

The prefrontal cortex (PFC) is thought to be involved in higher order cognitive functions, such as in working memory, abstract categorization, and reward processing. It has been reported that two distinct neuron classes (putative pyramidal cells and interneurons) in the PFC played different functional roles in neural circuits involved in forming working memory and abstract categories. However, it remains elusive how the two types of neurons process reward information in the PFC. To investigate this issue, the activity of single neurons was extracellularly recorded in the PFC of the monkey performing a reward predicting task. PFC neurons were classified into putative pyramidal cells and interneurons, respectively, based on the waveforms of action potentials. Both the two types of neurons encoded reward information and discriminated two reward conditions (the preferred reward condition vs. the nonpreferred reward condition). However, the putative pyramidal neurons had better and more reliable discriminability than the putative interneurons. Also, the pyramidal cells represented reward information in the preferred reward condition, but not in the nonpreferred reward condition by raising their firing rates relative to the baseline rates. In contrast, the interneurons encoded reward information in the nonpreferred reward condition, but not in the preferred reward condition by inhibiting their discharge rates relative to the baseline rates. These results suggested that the putative pyramidal cells and interneurons had complementary functions in reward processing. These findings may help to clarify individual functions of each type of neurons in PFC neuronal circuits involved in reward processing.