Tuning noninvasive brain stimulation with MRI to cope with intersubject variability

Abstract

a,c,dPurpose of review The review aims at highlighting the additional benefit that can be gained from combining noninvasive brain stimulation as well as repetitive sensory stimulation protocols with MRI techniques to account for the intersubject variability observed in those treatments. Potentially, this should help to identify predictive patterns in the individual receptiveness to the treatment. Recent findingsKnowledge about the underlying physiological principles of excitability changes as induced by noninvasive brain stimulation or repetitive sensory stimulation is accumulating, revealing strong associations with plasticity processes at the synaptic level. In this context, MRI techniques, such as magnetic resonance spectroscopy and functional MRI, emerged as valuable tools for the qualitative assessment of baseline states and induced changes. Those physiological readouts can help explain the interindividual heterogeneity found in behavioural and/or clinical responses to the specific stimulation protocols. This knowledge will eventually translate, first, into the preliminary classification of study participants into treatment groups according to their neurophysiological baseline state and expected responses to a particular stimulation. Subsequently, this should also aid the optimization of stimulation protocols according to the classification outcome, resulting in retuned protocols for particular groups of study participants. SummaryThe consistent MRI-based monitoring of stimulation effects in the neural network promises a considerable gain for the customization of intervention protocols with improved therapeutic potential and rehabilitative predictions.

Anodal tDCS Enhances Verbal Episodic Memory in Initially Low Performers

“…While tDCS helped elderly participants to regain a brain activation pattern found in younger individuals ( Meinzer et al, 2013 ), tDCS-induced benefits in healthy young adults seem to be limited by an inherent threshold, which requires further characterisation. Behavioral measures, however, might be too superficial to be used as a predictor whereas neurophysiological parameters like neurotransmitter levels and neural oscillations might represent better options ( Habich et al, 2016 ). This is all the more relevant as previous studies in the primary motor cortex revealed positive correlations between the magnitude of the anodal tDCS-induced γ-aminobutyric acid (GABA) decrease and the performance in a force-adaptation task ( Kim et al, 2014 ) and motor sequence learning, respectively ( Stagg et al, 2011 ).…”

No Effect of Anodal tDCS on Verbal Episodic Memory Performance and Neurotransmitter Levels in Young and Elderly Participants

“…For the most part, earlier studies focussed on the separate exploration of tDCS effects on behaviour on the one hand and the influence of the stimulation on neurophysiological measures on the other hand. Only the combination of all three aspects (i.e., tDCS, behavioural, and neurophysiological measures) in a single study provides an adequate setting to test if and how changes induced by tDCS on a neurophysiological level produce performance changes in cognitive paradigms [ 66 ]. Heretofore, research in the primary motor cortex is the vanguard in this kind of combinatorial study design and produced relatively consistent outcomes.…”

Der Einfluss von nicht invasiver transkranieller Stromstimulation auf das assoziative episodische Gedächtnis

“…Die Inter-Individuelle-Variabilität in der Anatomie des Schädels und des Gehirns wird dabei jedoch nicht beachtet, was zu einem inakkuraten Modelling führen und daher das Ergebnis der Studie beeinflussen könnte. Hier sind, wie bereits erwähnt, mittels fMRT-Technik Spezifizierungen möglich(Habich et al 2016). Fertonani und Miniussi 2017).…”