Post by Shireen Parimoo
What's the science?
Cognitive control is the ability to flexibly adapt behavior in the face of changing goals or demands, and it involves suppressing irrelevant information in the presence of conflict. The medial prefrontal cortex (mPFC) is thought to be involved in exerting control during conflict or during errors, after which behavior must be adjusted. Recent research also suggests that neural oscillations in the subthalamic nucleus (STN) are closely linked with those in the mPFC during conflict. However, it is unclear how changes in neural activity in the mPFC and STN are related to behavioral responses during tasks requiring varying levels of cognitive control. This week in Brain, Zavala and colleagues used intracranial electroencephalography and electrode recordings to investigate oscillatory activity in the mPFC and STN during a cognitive control task.
How did they do it?
Neural activity was recorded from 22 Parkinson’s disease patients who were undergoing deep brain stimulation surgery. Local field potentials and multiunit spiking activity were recorded from the STN using depth electrodes, and intracranial electroencephalography recordings were obtained from the superior mPFC. The participants performed a cognitive control task with three trial types: Go, Conflict, and No-go trials. In the Go trials, an arrow was presented on the screen, and participants had to move a joystick in the direction of the arrow; in the Conflict trials, participants had to move the joystick in the opposite direction to the arrow on the screen. In the No-go trials, they had to withhold their response. Feedback was provided at the end of each trial. The authors determined the average oscillatory power (or amplitude) for each trial type in the theta (2-5 Hz) and beta (8-30 Hz) frequency bands, which provided an index of the strength of oscillatory activity on a given trial. They also computed the phase coherence between the STN and the mPFC, which is a measure of the consistency of the phase of oscillatory signals. Higher phase coherence indicates that there is greater synchronization of activity between the two regions.
What did they find?
Participants made more errors and were slower on the Conflict trials. They were also slower and less accurate on Go trials that occurred after Conflict trials, compared to consecutive Go trials. In the No-go and Conflict trials, just before participants made a response, there was an increase in theta power in both the mPFC and the STN. This increase occurred several hundred milliseconds earlier in the mPFC than the STN and was greater during Conflict trials than the Go trials. During No-go trials in which a response had to be withheld, there was a large increase in theta power in the mPFC but a small change in the STN. Similarly, multiunit activity in the STN decreased during No-go trials, but greatly increased during Conflict trials that required inhibiting a prepotent response and performing the opposite movement. This indicates that the mPFC is involved in providing top-down signals to indicate that behavior must be adjusted, whereas the STN is responsible for modulating the actual behavioral response. Theta phase coherence was higher during Conflict and No-go trials than during the Go trials. As pre-response theta power increased before participants made a response, it suggests that theta oscillations are involved in adjusting cognitive control within trials, especially when the demand for control is high.
Beta power in the STN decreased prior to the participants’ response, whereas beta power in the mPFC increased after the response. In the mPFC, post-response beta power was lower during Conflict trials and when participants made an error. Conversely, beta power in the STN on a given Go trial was modulated by Conflict and errors on the previous trial. That is, beta power was higher on Go trials that occurred after Conflict trials. A similar pattern of activity was observed during Go trials that occurred after participants made an error, compared to Go trials that occurred after participants provided a correct response. Thus, beta oscillations in the STN may regulate responses in situations requiring a change in behavior, such as after an error is made or after high conflict trials.
What's the impact?
This study is the first to show how changes in oscillatory activity in the mPFC and the STN contribute to different aspects and temporal stages of cognitive control. Theta oscillations are involved in control during a trial, while beta oscillations play a role in exerting control across trials, particularly when control demands are higher. This research has important implications for understanding conditions in which cognitive control is impaired, such as schizophrenia and dementia.
Zavala et al. Cognitive control involves theta power within and beta power across trials in the prefrontal-subthalamic network. Brain (2018). Access the original scientific publication here.