Activity in the ?-frequency band (15-29Hz) is a highly prominent feature of neural recordings found across species, recording techniques, and spatial scales. Changes in ?-activity are particularly prominent during motor processes. Movement-related ?-activity can be observed in the cortical areas of the pyramidal motor system, as well as in the subcortical areas of the extrapyramidal motor system. Pathological ?-activity is a hallmark of movement disorders, most prominently of Parkinson's Disease (PD). Indeed, ?-activity is used both as a neurophysiological marker of disease progression in PD and as a target in newly developed, cutting-edge treatment methods such as closed-loop adaptive neurostimulation. However, recent studies in non-human animals have cast a fundamental layer of doubt on the nature of this neural signal and its relationship to behavior. Past studies of ?-activity have focused on averaged changes of signal-power across time (or across trials of a task), as is typical in neurophysiological studies. What recent studies have shown, however, is that unaveraged ?-band activity is not characterized by the type of steady (de)synchronizations of activity that are found in the average. Instead, ? is characterized by short, transient, burst-like `events'. The burst-like nature of this signal, however, is lost in the average ? and along with it, the systematic relationships that can be found between dynamics of these ?-burst events and motor control on individual trials. Therefore, there is a critical need to investigate how burst-like ?-events relate to both normal and pathological motor control in humans. We here propose a detailed, systematic investigation of this relationship. In an extensive pilot investigation, we have found that both human movement initiation and movement cancellation are accompanied by highly specific and systematic patterns of non-invasively recorded ?-bursts. This suggests the overarching hypothesis that ?- bursts are a universal signature that signify inhibitory processes in the motor system. The work in this grant proposal aims to systematically test this guiding hypothesis by linking specific patterns of ?-bursts to established theoretical models of motor inhibition in the human brain, by investigating the origins of movement-related ?- bursts in both cortical and subcortical regions that constitute the human motor system, and by providing causal evidence for the role of ?-bursts in conveying inhibitory motor control commands across the motor system.
The current proposal aims to investigate the dynamics of burst-like ?-frequency (15-29Hz) events in the human neural field potential in relation to both healthy and abnormal motor control. ?-band activity is a key signature of both pathological and normal movement in humans, but recent high-impact work has shown that existing research mischaracterized the burst-like nature of this signal, casting doubt upon established relationships between ?-activity and movement. This proposal aims to systematically investigate whether burst-like ?-activity reflects specific inhibitory control functions in the human motor system, thereby motivating a novel, detailed, neurophysiologically grounded understanding of motor control in both health and disease.
