Elsevier

Brain Stimulation

Volume 1, Issue 4, October 2008, Pages 326-336
Brain Stimulation

Original Research
Efficacy of repetitive transcranial magnetic stimulation/transcranial direct current stimulation in cognitive neurorehabilitation

https://doi.org/10.1016/j.brs.2008.07.002Get rights and content

Summary

Cognitive deficits are a common consequence of neurologic disease, in particular, of traumatic brain injury, stroke, and neurodegenerative disorders, and there is evidence that specific cognitive training may be effective in cognitive rehabilitation. Several investigations emphasize the fact that interacting with cortical activity, by means of cortical stimulation, can positively affect the short-term cognitive performance and improve the rehabilitation potential of neurologic patients. In this respect, preliminary evidence suggests that cortical stimulation may play a role in treating aphasia, unilateral neglect, and other cognitive disorders. Several possible mechanisms can account for the effects of transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) on cognitive performance. They all reflect the potential of these methods to improve the subject's ability to relearn or to acquire new strategies for carrying out behavioral tasks. The responsible mechanisms remain unclear but they are most likely related to the activation of impeded pathways or inhibition of maladaptive responses. Modifications of the brain activity may assist relearning by facilitating local activity or by suppressing interfering activity from other brain areas. Notwithstanding the promise of these preliminary findings, to date no systematic application of these methods to neurorehabilitation research has been reported. Considering the potential benefit of these interventions, further studies taking into consideration large patient populations, long treatment periods, or the combination of different rehabilitation strategies are needed. Brain stimulation is indeed an exciting opportunity in the field of cognitive neurorehabilitation, which is clearly in need of further research.

Section snippets

Transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) is a technique that uses a magnetic field, inducing an electrical current in the underlying brain tissue,6 which interacts with ongoing activity in the neural tissue. Trains of repetitive stimuli (rTMS), present the opportunity to interact even more effectively with cortical activity.7, 8, 9

Interference with cognitive processing when TMS is applied during performance of a task is called online TMS.10 In contrast, in the case of offline stimulation, TMS is

Online studies

Online TMS applied over cortical areas involved in verbal processing (perisylvian cortex of the dominant, usually left hemisphere) has been reported to facilitate picture naming and other language-related tasks in healthy subjects,22, 23, 24, 25, 26, 27, 28, 29 as well as in epileptic patients.15 Similar facilitatory effects of online rTMS were observed with picture naming after stimulation of prefrontal cortices (PFCs) in healthy volunteers15 and in patients with Alzheimer's disease (AD).30

Online studies

Enhancement of visual attention functions has been found in healthy subjects after stimulation of the parietal cortex.14, 56, 57 RTMS can be seen in this area as a interventional tool in sensory extinction58, 59 or unilateral neglect60, 61, 62 patients. Unilateral neglect can be defined as a defective ability to orient, detect, and report novel stimuli presented in the hemispace contralateral to the brain lesion, in which cannot be attributed to sensory-motor impairment functions (ie,

Transcranial direct current stimulation

At the end of the last century, another stimulation technique received renewed attention from the scientific community,72, 73 although knowledge of its existence and documentation of its clinical applications date back, at least, at the beginning of the 19th century.74 This method relies on application of direct currents (DC) and is known as transcranial DC stimulation (tDCS).73, 75, 76 Electrical currents are applied constantly at low intensities (1-2 mA) over a long period, usually in minutes

General discussion

The effects induced by rTMS or tDCS stimulation on cortical function are complex. The observed behavioral modifications reflect changes in cortical activity, which are dependent on a number of variables, such as the frequency of stimulation, its polarity, duration, intensity, and the site of stimulation. Moreover, we should bear in mind that the brain does not react passively to cortical stimulation, but that the response depends on its state of activation. It has been shown that offline rTMS

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