Oscillatory Activities in Neurological Disorders of Elderly: Biomarkers to Target for Neuromodulation

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.

Transcutaneous Vagus Nerve Stimulation Modulates EEG Microstates and Delta Activity in Healthy Subjects

“…Delta waves (1–4 Hz) are the most prominent EEG feature of human non-rapid eye movement (NREM) sleep, which have their origin in the cortical layer. Several studies proposed them as sensors for weighing synaptic efficacy and possible effectors of sleep-dependent synaptic plasticity [ 37 , 38 ]. Furthermore, wakefulness delta power increase was correlated with TMS-induced LTP-like plasticity in healthy subjects [ 37 ] and in patients with chronic stroke [ 39 ], as well as with local sleep regulation, functionally linked to learning-related cortical plasticity [ 40 ].…”

Multi-frequency tACS has lasting effects on neural synchrony and audiovisual responses

“…The observed effects on sensory responses promise a means to alter, over extended time periods, aspects of brain function that govern perception and behavior. Follow-up studies, in particular with use of subdural large-scale recordings in chronic preparations, could further promote the development of tACS as a tool to re-adjust brain states in pathological conditions of disturbed functional connectivity [10,12,25].…”

“…Impairment of proper coupling may lead to disorders, such as AD, PD, epilepsy, schizophrenia and autism [9]. This has fueled research into noninvasive approaches to modulate and, possibly, re-adjust neural synchrony by transcranial alternating current stimulation (tACS) [10][11][12][13][14].…”

Metronidazole Encephalopathy EEG Features: A Case Report with Systematic Review of the Literature

“…The increase in theta activity is usually caused by an alteration of the underlying brain tissue or its network [33], and specific theta/beta (4-25 Hz) oscillations of the granule cell layer in the cerebellum have been linked to cerebral cortex activity [32,34]. Di Lazzaro and colleagues have shown that cerebellar functional lesions produced by transcranial magnetic stimulation (TMS) produce an increase in theta EEG activity in frontal areas, suggesting a direct link between cerebellar dysfunction and increased EEG theta frontal activity [35].…”