Abstract
The medial prefrontal cortex (mPFC) is thought to control the shift from automatic to controlled action selection when conflict is present or when mistakes have been recently committed. Growing evidence suggests that this process involves frequency specific communication in the theta (4–8Hz) band between the mPFC and the subthalamic nucleus (STN), which is the main target of deep brain stimulation (DBS) for Parkinson's disease. Key in this hypothesis is the finding that DBS can lead to impulsivity by disrupting the correlation between higher mPFC oscillations and slower reaction times during conflict. In order to test whether theta band coherence between the mPFC and the STN underlies adjustments to conflict and to errors, we simultaneously recorded mPFC and STN electrophysiological activity while DBS patients performed an arrowed flanker task. These recordings revealed higher theta phase coherence between the two sites during the high conflict trials relative to the low conflict trials. These differences were observed soon after conflicting arrows were displayed, but before a response was executed. Furthermore, trials that occurred after an error was committed showed higher phase coherence relative to trials that followed a correct trial, suggesting that mPFC–STN connectivity may also play a role in error related adjustments in behavior. Interestingly, the phase coherence we observed occurred before increases in theta power, implying that the theta phase and power may influence behavior at separate times during cortical monitoring. Finally, we showed that pre-stimulus differences in STN theta power were related to the reaction time on a given trial, which may help adjust behavior based on the probability of observing conflict during a task.
Highlights
Being able to execute tasks quickly and accurately is a key skill
We build on our previous work in which we have separately shown that the flanker task induces theta band phase locking which entrains individual subthalamic nucleus (STN) neurons (Zavala et al, 2013, 2015a) and that mesial frontal cortex theta oscillations drive those of the STN in a gradually evolving conflict task that did not involve stimulus locked theta phase locking (Zavala et al, 2014)
There was no Gratton effect on reaction time (Gratton et al, 1992): the reaction time of high conflict trials was not affected by the level of conflict in the previous trial (p N 0.05, signed rank test ), and the same was true for low conflict trials (p N 0.05, signed rank test)
Summary
Being able to execute tasks quickly and accurately is a key skill. as important, is the ability to dynamically alter the amount of time dedicated to a task based on the task's difficulty and based on previous performance. One area of the brain implicated in speed-accuracy trade off, in scenarios that require a quick action in the face of conflict, is the medial prefrontal cortex (mPFC). Previous work has shown that mPFC activity is higher for high conflict tasks (Botvinick et al, 2004; Sheth et al, 2012) it is directly correlated to the reaction time during conflict (Cavanagh et al, 2011; Cohen and Cavanagh, 2011; Cohen and Donner, 2013). According to some models (Cavanagh et al, 2011, 2012; Cohen and Cavanagh, 2011), increased mPFC theta band (4–8 Hz) activity is thought to increase the amount of evidence that has to be integrated by the brain prior to the selection of an action (i.e. increased “evidence threshold”). The mechanisms by which the mPFC is able to rapidly and dynamically alter behavior, are still unclear
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