Browsing by Subject "stopping"

The general question of this research is how beta oscillations are implicated in stopping an ongoing movement. Previous studies regarding movement cancellation have found a significant increase in beta activity in sensorimotor areas, especially in the form of transient increases in beta oscillations, called beta bursts. However, the functional role of beta band activity in stopping is still unclear, mainly because the behavioural tasks used cannot measure the exact timing when the subjects start the stopping process and therefore it is only possible to infer the stopping time. To resolve this, we used head-fixed rats running on a treadmill while performing a Go/NoGo task. In some NoGo trials, the rat starts to run, realizes the mistake and stops before crossing a fixed distance threshold. These are the events being analyzed, called near-mistake events (N=39,366). We found a single beta burst occurring prior to stopping in all five brain regions analyzed (from 44.2±20.1 ms to 55.8±16.0 ms) and positive correlations of beta burst number and power increase with movement speed before stopping. We also found a single alpha burst prior to and during stopping in all brain regions (from 45.9±20.1 ms to 57.1±19.3 ms), supporting previous studies’ findings of alpha band involvement in inhibitory motor actions. Our findings on beta bursts suggest a causality role in stopping an ongoing movement while our results of alpha bursts need to be further analyzed to understand its functional role.

Beta frequency (15-25 Hz) oscillations in the extracellular field potential recorded by cortical EEG and depth electrodes have been connected to stopping. Especially short increases in beta power, so called beta bursts, occur more frequently close to stopping an ongoing movement or when cancelling a planned action. However, there are discrepancies about the causal role of these beta bursts on stopping. Although some studies indicate causality, in others the bursts occur too late for being causal or their number does not increase prior to stopping. One explanation to the disagreement may lie in the behavioral task commonly used to study the neural correlates of action inhibition, the stop signal task. In this task the movement is cancelled before it starts, and actual stopping is thus hidden from the experimenter. Instead, an estimated stop signal reaction time is mathematically modelled. It is likely that this reaction time varies trial by trial, which causes inaccuracy in the results. We were able to define an exact stopping time using head fixed rats running on a treadmill. This enabled us to align brain activity precisely with stopping. With this task, we showed that the number of transient beta bursts increases just prior to stopping. Moreover, the increase correlates with the velocity. These results indicate that beta bursts are causal to stopping. Beta bursts have been noted to be disturbed in Parkinson’s disease and our results may open new doors for early diagnoses or treatments.