Unreliable feedback leads to changes in EEG in Parkinson’s disease
A study by Maarten van den Heuvel and colleagues from the VU University and VU Medical Centre in Amsterdam shows differences in EEG characteristics between patients with Parkinson’s disease and healthy controls when incongruent feedback is provided. The results, published in the upcoming issue of the journal Clinical Neurophysiology, support the idea that some patients with PD show unwarranted higher confidence in visual feedback (VF) during perceptual-motor tasks.
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Parkinson’s disease (PD) is a complex disease, confronting patients with impairments in movement-related capacities, as well as in a variety of aspects that are not movement-related. Characteristic (motor) components of the disease are slowness of movement, difficulties initiating a movement, trembling, and postural instability. It has been long known that cueing strategies, in which one tries to synchronize one’s movements with a (rhythmic) external stimulus, can help to facilitate motor performance. At the same time, observations across a wide spectrum of tasks, including balance tasks, suggest that patients with PD overly rely on visual information.
To provide helpful strategies to patients it is thus essential to answer the question: when do visual cues help, and when do they hurt? In a previous study we found that patients with PD are less proficient in adapting to situations with incongruent VF than healthy controls. Recent research in PD patients suggests that certain EEG-parameters may have a role in assessing the reliability of such sensory feedback.
In the present study, we used EEG to investigate motor-related activation in the cortex during a postural task. Subjects were asked to follow an oscillating target, shown on a monitor, by swaying their body from left to right. During the task, subjects received continuous feedback, which was congruent (i.e. reliable) in some conditions, and incongruent (i.e. unreliable) in other conditions. We compared the activity of 24 patients with PD with that of 15 healthy controls.
For congruent VF no significant differences in cortical activity between the two groups were present. Yet for incongruent VF, the PD group showed significantly higher beta modulation in primary motor cortex, and higher alpha modulation in primary visual cortex. In other words, both in the motor network and in visual areas some EEG-parameters discriminated between groups, suggesting partially altered visuomotor processing in PD patients. We hypothesize that the unwarranted higher confidence in VF in the PD group is related to the observed differences in alpha/beta modulation.