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.

Keywords: brain stimulation; chronic aphasia; long term effects; stroke; tDCS.

Figures

Figure 1

The figure shows a single CT scan acquisition of all the three patients. (A) Patient #1 suffered from a left (fronto)temporal hemorrhage. (B) Patient #2 had a left frontal ischemic stroke. (C) Patient #3 had a left temporal hemorrhage.

Figure 2

Overview of experimental design. All three patients underwent a daily naming training (first list of 40 figures) for five consecutive days. Concurrently, tDCS (20 min) was administered over the left frontal region. Two stimulations were given: first sham, then anodal, with a 60-min pause interval. After a 2-day pause interval, all the patients underwent a second daily naming training with a second list of 40 figures (more difficult in terms of word frequency). The same simultaneous tDCS paradigm was applied. At the beginning of each week (to measure baseline performance), at the end of the stimulation period, after 4, 8, 12, 16, and 21 weeks (first, second, third, fourth, and fifth follow-up), patients were shown the two lists of figures and asked to name them. The Aachener Aphasia Test (AAT) and the Boston Naming Test (BNT) were administered 1 week before the experiment, at the end of each stimulation period and at each follow-up (not shown in the figure).

Figure 3

Statistical analysis of the on-line effects of A-tDCS vs S-tDCS (McNemar test) on the first (left) and second (right) naming training. (A) Patient #1; (B) Patient #2; (C) Patient #3.

Figure 4

Follow-up observation after the end of on-line A-tDCS: statistical analysis on the patients’ naming performance for naming list 1, naming list 2, Aachener Aphasie Test (AAT) and Boston Naming Test (BNT). (A) Patient #1; (B) Patient #2; (C) Patient #3.