Abstract
Non-invasive brain stimulation (NIBS) has been under investigation as adjunct treatment of various neurological disorders with variable success. One challenge is the limited knowledge on what would be effective neuronal targets for an intervention, combined with limited knowledge on the neuronal mechanisms of NIBS. Motivated on the one hand by recent evidence that oscillatory activities in neural systems play a role in orchestrating brain functions and dysfunctions, in particular those of neurological disorders specific of elderly patients, and on the other hand that NIBS techniques may be used to interact with these brain oscillations in a controlled way, we here explore the potential of modulating brain oscillations as an effective strategy for clinical NIBS interventions. We first review the evidence for abnormal oscillatory profiles to be associated with a range of neurological disorders of elderly (e.g., Parkinson’s disease (PD), Alzheimer’s disease (AD), stroke, epilepsy), and for these signals of abnormal network activity to normalize with treatment, and/or to be predictive of disease progression or recovery. We then ask the question to what extent existing NIBS protocols have been tailored to interact with these oscillations and possibly associated dysfunctions. Our review shows that, despite evidence for both reliable neurophysiological markers of specific oscillatory dis-functionalities in neurological disorders and NIBS protocols potentially able to interact with them, there are few applications of NIBS aiming to explore clinical outcomes of this interaction. Our review article aims to point out oscillatory markers of neurological, which are also suitable targets for modification by NIBS, in order to facilitate in future studies the matching of technical application to clinical targets.
Highlights
Oscillatory activities in neural systems may play a functional role (Gray, 1994) and abnormalities in neural synchronization mechanisms might be involved in the pathophysiology of several neuropsychiatric disorders (Uhlhaas and Singer, 2006)
Progress has been limited despite the huge experimental efforts spent to identify Non-invasive brain stimulation (NIBS) applications that can be used during rehabilitation for additive treatment of motor and linguistic deficits in stroke, Parkinson disease, or for drug-resistant epilepsy, Alzheimer disease and psychiatric disorders
One clue may reside in the fact that, in most of the clinical trials, the only biological neurophysiological variable targeted by neuromodulation is cortical excitability and its marker, i.e., the amplitude of MEP
Summary
Oscillatory activities in neural systems may play a functional role (Gray, 1994) and abnormalities in neural synchronization mechanisms might be involved in the pathophysiology of several neuropsychiatric disorders (Uhlhaas and Singer, 2006). Alpha-band activity is the dominant oscillation in the awake human brain It is prominently observed over areas of the visual and attention network, where it is negatively related to visual perception (Hanslmayr et al, 2005; Thut et al, 2006), which is in line with the hypothesis that this frequency band plays an inhibitory role (Klimesch et al, 2007). After levodopa administration in PD patients, alpha-activity is increased in the pedunculopontine nucleus (PPN), bidirectionally-coupled with similar changes in cortical EEG, when participants perform self-paced movements (Androulidakis et al, 2008) These findings suggest a possible physiological role of these oscillations in the PPN area, such as promoting motor related attentional processes, which can be affected in non-treated PD. Beta activity should be considered in a wider context of information gating favoring the maintenance of the status quo of the selected neuronal system (pyramidal and extrapyramidal; Engel and Fries, 2010; Brittain and Brown, 2014; Figure 1)
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