Introduction: The alpha rhythm (8-14 Hz) is thought to reflect a mechanism of functional inhibition, regulating the engagement and disengagement of neuronal populations based on task demands. Broadband activity in the high gamma range (70-150 Hz) is considered a correlate of multi-unit activity. We track activity within these two frequency bands across a range of cortical areas using electrocorticography recordings in human patients with intractable epilepsy performing a cognitive interference task that allows us to address various cognitive aspects including attention, perception, decision-making and the subsequent motor response.
Methods: Subjects performed the multi-source interference task (MSIT), which combines elements of the Stroop, Simon, and Eriksen flanker tasks. We recorded ECoG activity from 18 subjects with coverage over a broad range of frontal, temporal, and parietal regions.
Results: We find a negative relationship between alpha power and broadband high gamma activity. Combined, these activation patterns reflect temporal tracking of task-engaged regions, with alpha decrease and broadband increase locked to specific task aspects. We report different categories of responses, distributed over cortex, including sites that only respond to the stimulus presentation, sites that only respond to the decision report and/or the feedback, and interestingly, sites that track the time on task. The latter allows prediction of behavioral performance in terms of reaction times. Furthermore, we find a small subset of sites that show modulation with task difficulty, predominantly in temporal areas, and modulation based on task history.
Conclusions: Our results support the notion that alpha reflects functional inhibition at the local neuronal population level, gating neuronal activity as reflected by broadband high gamma. Crucially, the combination of these signals correlates with various task aspects and allows us to predict behavioral performance. We provide evidence for the generality of this mechanism across cortical areas, including prefrontal cortex.
Patient Care: Understanding the networks responsible for decision-making in the human brain will lead to new advances in treating disorders of the involved networks.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Define alpha and high gamma band ranges;
2) Describe qualitative differences between alpha and high gamma;
3) Describe how interactions between the two shape human decision making.