The temporal context of certainty-uncertainty modulates the subthalamic nucleus-mediated anticipatory responding

Lesions of the subthalamic nucleus (STN) in the rat are known to induce anticipatory responses in the preparatory period preceding conditioned movements. This study aimed to investigate how the temporal context in which a stimulus is presented affects the anticipatory responding caused by a unilateral STN lesion. A reaction-time task was employed in which a trigger signal starting a bar-pressing movement was presented at either side of the head in two temporal contexts. In the first, the trigger was presented at a fixed delay (FD paradigm) of 1s following an instruction signal. In the second, the 1s delay was randomly distributed (RD paradigm) among other delays. Reaction time was faster in the FD paradigm with respect to the RD paradigm. An increased readiness to move was observed in animals engaged in the RD paradigm as the delay period shortened, and this function was not abolished by the STN lesion. Anticipatory responding in general was less pronounced than in other paradigms previously reported in the literature, and predominated in the RD paradigm with respect to the FD paradigm. The destruction of the STN worsened the anticipatory responding only in the FD paradigm. A major consequence of the STN lesion was an increase of unconditioned responses to the instruction signal starting each trial. This attention deficit was more pronounced in the RD paradigm with respect to the FD paradigm, and was subsequently worsened by the lesion in both paradigms. The results suggest that the anticipatory responding may depend on the level of uncertainty implicit in each behavioural paradigm whereas inappropriate responding to the behavioural cue starting a trial may be independent from this factor, and highlight the importance of the behavioural paradigms employed when dealing with STN functions.