Change in hippocampal theta oscillation associated with multiple lever presses in a bimanual two-lever choice task for robot control in rats.

Hippocampal theta oscillations have been implicated in working memory and attentional process, which might be useful for the brain-machine interface (BMI). To further elucidate the properties of the hippocampal theta oscillations that can be used in BMI, we investigated hippocampal theta oscillations during a two-lever choice task. During the task body-restrained rats were trained with a food reward to move an e-puck robot towards them by pressing the correct lever, ipsilateral to the robot several times, using the ipsilateral forelimb. The robot carried food and moved along a semicircle track set in front of the rat. We demonstrated that the power of hippocampal theta oscillations gradually increased during a 6-s preparatory period before the start of multiple lever pressing, irrespective of whether the correct lever choice or forelimb side were used. In addition, there was a significant difference in the theta power after the first choice, between correct and incorrect trials. During the correct trials the theta power was highest during the first lever-releasing period, whereas in the incorrect trials it occurred during the second correct lever-pressing period. We also analyzed the hippocampal theta oscillations at the termination of multiple lever pressing during the correct trials. Irrespective of whether the correct forelimb side was used, the power of hippocampal theta oscillations gradually decreased with the termination of multiple lever pressing. The frequency of theta oscillation also demonstrated an increase and decrease, before and after multiple lever pressing, respectively. There was a transient increase in frequency after the first lever press during the incorrect trials, while no such increase was observed during the correct trials. These results suggested that hippocampal theta oscillations reflect some aspects of preparatory and cognitive neural activities during the robot controlling task, which could be used for BMI

Nucleus accumbens neurons encode initiation and vigor of reward approach behavior

AbstractThe nucleus accumbens (NAc) is considered an interface between motivation and action, with NAc neurons playing an important role in promoting reward approach. However, the encoding by NAc neurons that contribute to this role remains unknown. Here, we trained male rats to find rewards in an 8-arm radial maze. The activity of 62 neurons, mostly in the shell of the NAc, were recorded while rats ran towards each reward place. General linear model (GLM) analysis showed that variables related to the vigor of the locomotor approach, like speed and acceleration, and the fraction of the approach run completed were the best predictors of the firing rate for most NAc neurons. Nearly 23% of the recorded neurons, here named locomotion-off cells, were inhibited during the entire approach run, suggesting that reduction in firing of these neurons promotes initiation of locomotor approach. Another 24% of the neurons presented a peak of activity during acceleration followed by a valley during deceleration (peak-valley cells). Together, these neurons accounted for most of the speed and acceleration encoding identified in the GLM analysis. Cross-correlations between firing and speed indicated that the spikes of peak-valley cells were followed by increases in speed, suggesting that the activity of these neurons drives acceleration. In contrast, a further 19% of neurons presented a valley during acceleration followed by a peak just prior to or after reaching reward (valley-peak cells). These findings suggest that these three classes of NAc neurons control the initiation and vigor of the locomotor approach to reward.Significance StatementDeciphering the mechanisms by which the NAc controls the vigor of motivated behavior is critical to better understand and treat psychiatric conditions in which motivation is dysregulated. Manipulations of the NAc profoundly impair subjects’ ability to spontaneously approach reward-associated locations, preventing them from exerting effort to obtain reward. Here, we identify for the first time specific activity of NAc neurons in relation to spontaneous approach behavior. We discover three classes of neurons that could control initiation of movement and the speed vs. time trajectory during locomotor approach. These results suggest a prominent but heretofore unknown role for the NAc in regulating the kinematics of reward approach locomotion.</jats:sec