Long-Term Effects of Transcranial Direct-Current Stimulation in Chronic Post-Stroke Aphasia: A Pilot Study

Abstract

Transcranial direct-current stimulation (tDCS) has been suggested to improve language function in patients with post-stroke aphasia. Most studies on aphasic patients, however, were conducted with a very limited follow-up period, if any. In this pilot, single-blind study on chronic post-stroke aphasic patients, we aimed to verify whether or not tDCS is able to extend its beneficial effects for a longer period of time (21 weeks after the end of stimulation). Three aphasic patients underwent anodal tDCS (A-tDCS, 20 min, 1.5 mA) and sham stimulation (S-tDCS) over the left frontal (perilesional) region, coupled with a simultaneous naming training (on-line tDCS). Ten consecutive sessions (5 days per week for 2 weeks) were implemented. In the first five sessions, we used a list of 40 figures, while in the subsequent five sessions we utilized a second set of 40 figures differing in word difficulty. At the end of the stimulation period, we found a significant beneficial effect of A-tDCS (as compared to baseline and S-tDCS) in all our subjects, regardless of word difficulty, although with some inter-individual differences. In the follow-up period, the percentage of correct responses persisted significantly better until the 16th week, when an initial decline in naming performance was observed. Up to the 21st week, the number of correct responses, though no longer significant, was still above the baseline level. These results in a small group of aphasic patients suggest a long-term beneficial effect of on-line A-tDCS.

Motor System Reorganization After Stroke: Stimulating and Training Toward Perfection

“…Many of the effects described above were only evident for a short period of time after stimulation, but more enduring motor improvements result from stimulation coupled with motor training (105,136,184,189). For example, tDCS paired with 10 consecutive occupation therapy sessions improved paretic upper limb function compared with therapy alone for up to 6 mo, as assessed with the Fugl-Meyer Score (102).…”

“…Vestito et. al (184) found that tDCS paired with practice in naming in aphasic patients improved naming performance for 16 wk compared with controls. There are emerging applications for transcranial stimulation in combination with robot-assisted training (60, 74) and brain-machine interfaces (73).…”

Use of Computational Modeling to Inform tDCS Electrode Montages for the Promotion of Language Recovery in Post-stroke Aphasia

“…Thus, the design and interpretation of most of the research addressed only the current delivered over the targeted region. This led to two neuromodulation strategies: either increasing excitability through anodal stimulation over the left hemisphere [5][6][7][8][9]11,[13][14][15][16]20,21] or by decreasing excitability in the contralesional language homologue areas using cathodal stimulation in order to attenuate the inhibition from the intact right hemisphere [10,12,15,[17][18][19][20]. Indeed, while in the context of acute or subacute lesions of the left hemisphere language network there appears to be greater tendency for reallocation of language function into the right-hemisphere perisylvian circuits, many studies have shown that, over time, there is, for a number of patients at least, diminished recruitment of right hemisphere structures for language tasks with a redistribution of language processing back to the left hemispheric perisylvian areas [22][23][24].…”

“…In the past decade, researchers have investigated the use of noninvasive neuromodulation techniques and, in particular, transcranial direct current stimulation (tDCS) to promote language recovery in poststroke aphasia [3]. While the first published study [4] that documented tDCS use for aphasia rehabilitation did not include a behavioral treatment protocol, studies since then have combined tDCS with speech-language therapy [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. These initial studies generally included behavioral treatment for anomia and implemented noun retrieval as the outcome measure; more recent studies have included additional behavioral treatments for the recovery of verbs [5,7,13], articulation [9] and discourse productivity [6,8].…”

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“…In contrast, tDCS is less expensive than rTMS; a typical tDCS apparatus is batteryoperated, highly portable, and easy to use. In some clinical settings, the effects of tDCS appear to last longer than those of rTMS 18,19 . Furthermore, tDCS has been shown to confer polarity-dependent effects on brain excitability.…”