Technology Insight: noninvasive brain stimulation in neurology—perspectives on the therapeutic potential of rTMS and tDCS

Abstract

In neurology, as in all branches of medicine, symptoms of disease and the resulting burden of illness and disability are not simply the consequence of the injury, inflammation or dysfunction of a given organ; they also reflect the consequences of the nervous system's attempt to adapt to the insult. This plastic response includes compensatory changes that prove adaptive for the individual, as well as changes that contribute to functional disability and are, therefore, maladaptive. In this context, brain stimulation techniques tailored to modulate individual plastic changes associated with neurological diseases might enhance clinical benefits and minimize adverse effects. In this Review, we discuss the use of two noninvasive brain stimulation techniques--repetitive transcranial magnetic stimulation and transcranial direct current stimulation--to modulate activity in the targeted cortex or in a dysfunctional network, to restore an adaptive equilibrium in a disrupted network for best behavioral outcome, and to suppress plastic changes for functional advantage. We review randomized controlled studies, in focal epilepsy, Parkinson's disease, recovery from stroke, and chronic pain, to illustrate these principles, and we present evidence for the clinical effects of these two techniques.

Bilateral Transcranial Direct Current Stimulation Modulates Activation-Induced Regional Blood Flow Changes during Voluntary Movement

“…It has also been suggested that bilateral tDCS stimulation might bear some advantage for stroke rehabilitation over unilateral application, since the anodal electrode placed over the affected hemisphere would facilitate recruitment of the affected motor cortex directly while the cathode placed over the unaffected hemisphere would reduce transcallosal inhibition to the affected hemisphere and facilitate movement in the affected limb, indirectly (Fregni and Pascual-Leone, 2007;Schlaug and Renga, 2008). The results from our study do not directly support this hypothesis because we only found cathodal stimulation to be effective in terms of MEP and rCBF changes, thus favoring the reduction of transcallosal inhibition as the stronger pathophysiological principle (Traversa et al, 1998).…”

Working memory improvement with non-invasive brain stimulation of the dorsolateral prefrontal cortex: A systematic review and meta-analysis

“…TDCS generates low-intensity electric fields (Datta et al, 2009) in the brain leading to small changes (<1 mV) (Radman, Ramos, Brumberg, & Bikson, 2009) in the membrane potential, thus influencing the frequency of spike timing and modifying net cortical excitability (Purpura & McMurtry, 1965) without triggering action potentials per se (Brunoni et al, 2012;Nitsche et al, 2008). In turn, rTMS causes disruptions in brain activity by delivering strong magnetic pulses to the cortex that pass through the skull and depolarize the underlying neurons of particular areas in the brain Repetitive TMS over the motor cortex facilitates or inhibits brain excitability according to the frequency of stimulation (respectively >1Hz and <1Hz) (Fregni & Pascual-Leone, 2007;George & Aston-Jones, 2010;Hallett, 2007) For cognitive functions, however, there are also other factors that determine rTMS effects, particularly the baseline activity state of the stimulated region ("state-dependency") (Sandrini, Umilta, & Rusconi, 2011;Silvanto, Cattaneo, Battelli, & Pascual-Leone, 2008;van de Ven & Sack, 2013). For instance, Soto et al (2012) observed that the application of TMS during a WM task respectively increased and decreased accuracy whether the cues were valid or invalid.…”

Optogenetic neuronal stimulation promotes functional recovery after stroke

“…The primary motor cortex (M1) is a commonly stimulated area as it directly innervates the corticospinal tract to initiate movement (1,7). Although electrical stimulation and transcranial magnetic stimulation show promise in promoting recovery (17,18), these techniques are limited by imprecision and indiscriminate activation or inhibition of all cell types near the stimulated site; thus, they can produce undesired effects such as psychiatric and motor/speech problems (19)(20)(21). In addition, it has been difficult to elucidate the cell type and mechanisms driving recovery, as multiple cell types such as neurons, astrocytes, and oligodendrocytes have been shown to contribute to remodeling and recovery processes after stroke (5,(22)(23)(24)(25)(26)(27).…”