Awareness of its rich structural pathways has earned the external segment of the globus pallidus (GPe) recognition as a central figure within the basal ganglia circuitry. Interestingly, GPe neurons are uniquely identified by the presence of prominent pauses interspersed among a high-frequency discharge rate of 50-80 spikes/s. These pauses have an average pause duration of 620 ms with a frequency of 13/min, yielding an average pause activity (probability of a GPe neuron being in a pause) of (620 × 13)/(60 × 1000) = 0.13. Spontaneous pause activity has been found to be inversely related to arousal state. The relationship of pause activity with behavioural events remains to be elucidated. In the present study, we analysed the electrophysiological activity of 200 well-isolated GPe pauser cells recorded from four non-human primates (Macaque fascicularis) while they were engaged in similar classical conditioning tasks. The isolation quality of the recorded activity and the pauses were determined with objective automatic methods. The results showed that the pause probability decreased by 9.09 and 10.0%, and the discharge rate increased by 2.96 and 1.95%, around cue and outcome presentation, respectively. Analysis of the linear relationship between the changes in pause activity and discharge rate showed r2 = 0.46 and r2 = 0.66 upon cue onset and outcome presentation, respectively. Thus, pause activity is a pertinent element in short-term encoding of relevant behavioural events, and has a significant, but not exclusive, role in the modulation of GPe discharge rate around these events. Four primates have been trained in classical conditioning tasks where visual cues are associated with reward, aversive or neutral outcome. Neuronal activity of 200 external globus pallidus high frequency discharge pauser cells was analysed. Upon conditioned stimulus or outcome onset, there was an increase in discharge rate and a decrease in pause activity indicating an inverse relationship between the two and suggesting functional relevance of pause activity in encoding behavioral events.
Bibliographical notePublisher Copyright:
© 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.
- Basal ganglia
- Classical conditioning
- Firing rate modulation
- Pause probability