Conditioned enhancement of firing rates and synchrony of hippocampal neurons and firing rates of motor cortical neurons in rats.

The aim of this study was to examine the potential ability of neuronal groups to enhance their activities by conditioning without behaviors. We employed a method of neuronal operant conditioning in which increments in the firing rates and synchrony of closely neighboring neurons in the motor cortex and hippocampus were rewarded in the absence of behaviors. Rats were trained to engage in a free-operant task in which nose-poke behaviors were rewarded in session 1, and firing rates and synchrony above preset criteria were rewarded in sessions 2 and 3, respectively. The firing rates of motor cortical and hippocampal neuron groups were found to increase rapidly in session 2 similarly to the nose-poke behavior in session 1. Placing contingency of reward on firing synchrony resulted in selective enhancement of firing synchrony of only hippocampal neurons in session 3. Control experiments revealed that the enhancement of neuronal firing was not attributable to increments of superstitious behaviors or excitation caused by reward delivery. Analysis of the firing rates and synchrony of individual neurons and neuron pairs in each group revealed that the firing rates and synchrony of some but not all neurons and neuron pairs increased in each group. No enhancement was observed in any neurons and neuron pairs recorded by neighboring electrodes not used for conditioning. These results suggest that neuronal operant conditioning enhances the firing rates and synchrony of only some neurons in small restricted areas. The present findings are expected to contribute to further research into neurorehabilitation and neuroprosthesis.