Taking Sides: An Integrative Review of the Impact of Laterality and Polarity on Efficacy of Therapeutic Transcranial Direct Current Stimulation for Anomia in Chronic Poststroke Aphasia
Table 1
tDCS studies of naming ability of individuals with chronic poststroke aphasia. Images are supplied to illustrate key aspects of the protocol. Ovals represent stimulation site, with size reflecting electrode size. Red ovals represent anodal stimulation, blue ovals represent cathodal stimulation, and grey ovals represent sham stimulation. Symbols on the ovals indicate target site; symbols alone indicate reference electrodes.
2 mA, 10 mins, single sessions, electrodes 35 cm2 Experiment 1 At least a week between anodal or/and cathodal and sham
8 in total
None
Noun picture naming accuracy and reaction time
Naming accuracy increased significantly (+33.6%) following cathodal stimulation but not after anodal or sham stimulation There were no significant changes in reaction time following anodal, cathodal or sham stimulation
N/A
4 + 2 also cathodal
4 + 2 also anodal
24–96
4 × Broca’s 4 × Global
2 months later Experiment 2 Time between cathodal and sham not reported
Reference electrode on contralateral shoulder.
None
Noun picture naming accuracy and reaction time
There were no significant changes in either naming accuracy or reaction time following cathodal or sham stimulation
Noun and verb picture naming accuracy and reaction time
Anodal tDCS significantly improved verb picture naming accuracy (+184.62%) and reduced reaction time (−32.68%) for only 1 ppt, with the most severe anomia There were no significant effects of stimulation on noun picture naming accuracy and speed
Noun picture naming accuracy Treated and untreated items
Anodal tDCS significantly improved the naming accuracy of treated items and numerically increased (from 27.3 to 40/50 after treatment) the number of untreated items named correctly
1 week: the significant effect of anodal stimulation was maintained and the number of untreated items named correctly increased further (42/50, still n.s.)
1 mA, 20 mins × 5 days for 1 week, electrodes 25 cm2 3 weeks between anodal and sham
8
10–150
Fluent
Computerized noun naming therapy
Noun picture naming reaction time Treated and untreated items
Anodal tDCS significantly reduced reaction times (−455.57 ms) for 7/8 ppts on treated items versus sham tDCS (−281.17 ms) There were no significant effects of stimulation on untreated items
3 weeks: all 8 ppts now showed reduced reaction times for treated items after anodal tDCS (−430.6 ms) and not after sham tDCS (−265.86 ms)
1 mA, 20 mins × 5 days for 1 week, electrodes 35 cm2 One week between anodal and sham
3
21–71
Nonfluent (1 × mild, 1 × moderate, 1 × severe)
Computerized noun naming therapy
Noun picture naming accuracy and reaction time Treated items only
Naming accuracy significantly increased (+21% more than sham) and reaction time significantly reduced following anodal tDCS rather than sham tDCS (1486 ms versus 1763 ms)
1 and 3 weeks (only 2/3 ppts): some reduction in naming accuracy from the end of therapy to 1 week follow-up (still significant) effects on reaction times maintained
1 mA, 20 mins × 5 days for 1 week, electrodes 35 cm2 Six days between anodal Wernicke’s, anodal Broca’s and sham, one month between noun cycle and verb cycle
7
7–84
Nonfluent with noun and verb retrieval deficits
Computerized noun and verb naming therapy
Noun and verb picture naming accuracy Treated items only
Anodal tDCS to Broca’s area significantly improved verb naming accuracy (Broca’s versus Wernicke’s = +24%, Broca’s versus sham = +22%). Anodal tDCS to Wernicke’s area significantly improved noun naming accuracy (Wernicke’s versus Broca’s = +17%, Wernicke’s versus sham = +24%)
1 and 4 weeks: significant effects of Broca’s stimulation on verb naming and of Wernicke’s stimulation on noun naming persisted
1.5 mA, 20 mins × 5 days for 2 weeks, electrodes 25 cm2 Anodal one hour after sham
3
20–64
2 × nonfluent (1 × high, 1 × very high severity) 1 × Anomic (moderate severity)
Noun and verb naming therapy Therapy task difficulty was increased for the second week (different item set with increased number of lower frequency words)
Noun and verb picture naming accuracy Treated items only Boston Naming Test (BNT), Aachen Aphasia Test (AAT) (naming, oral/written comprehension)
Anodal stimulation significantly increased the number of items correctly named from baseline, with initial increases following the first session and further increases over the remaining sessions each week for ppt 1 (week 1 15/24/28, week 2 8/24/30) and ppt 3 (26/30/35, week 2 27/31/36), and for week 2 for ppt 2 (16/22/26) Therapy task difficulty was unrelated to naming outcomes Anodal stimulation increased % correct responses for all ppts on the BNT (ppt 2 and ppt 3 n.s.) and AAT (ppt 3 n.s.)
4, 8, 12, 16, and 21 weeks: effects on number of correct responses persisted significantly for all ppts to 16 weeks and persisted up to 21 weeks (n.s.) % correct responses on the AAT and BNT persisted significantly up to 12 weeks and persisted up to 21 weeks (n.s.)
1 mA, 15 mins × single sessions, electrodes 35 cm2 Two hours between cathodal and sham
25
>3 (mean = 15)
Picture naming deficits Range of severity of aphasia 11 ppts with lesions involving Broca’s area (B+), 14 with lesions not involving Broca’s area (B−)
None
Noun picture naming accuracy (calculated as a function of the number of correct and partially correct (e.g., containing one phonemic error) responses)
Naming accuracy of B+ ppts increased significantly following cathodal tDCS, naming accuracy of 13/14 of B− ppts decreased or remained the same following cathodal stimulation Greater improvements in naming were also associated with greater integrity of the arcuate fasciculus
1 mA, 20 mins × twice per day for 3 days (at start of each training hour), electrodes 35 cm2 3 weeks between anodal, cathodal and sham
12
14–260
2 × Anomic 7 × Broca’s 1 × Global 1 × Wernicke’s 1 × not classified
Computerized noun naming therapy involving a decreasing cueing hierarchy
Noun picture naming accuracy Treated items only
All conditions resulted in increased naming ability (= 83%), but anodal tDCS led to significantly greater improvements than cathodal or sham stimulation Ppts with more severe anomia showed the greatest therapy gains
2 mA, 30 mins, single sessions, electrodes 25 cm2, therapy given during last 15 minutes of stimulation >24 hours between anodal + sham and bilateral conditions Reference electrodes were placed over the ipsilateral buccinator muscles
11
6+
4 × Broca’s 2 × Transcortical motor 5 × Anomic
Picture naming and reading short paragraphs
Noun picture naming accuracy and reaction time on Korean version of the BNT Verbal fluency
Naming accuracy significantly increased in both conditions Reaction time decreased in both conditions, but this was only significant for the bilateral stimulation condition Stimulation had no effect on verbal fluency
2 mA, 25 minutes × 5 days for 4 weeks, electrodes 35 cm2 Anodal and cathodal delivered simultaneously
1
8
Mild nonfluent
None 25 minutes of semantic-phonological therapy given directly after each stimulation session
Nonverbal reasoning, verbal fluency, Aachen Aphasia Test (AAT), Battery for the Analysis of Aphasia Deficits (BADA), Stroke and Aphasia Quality of Life Scale-39 (SAQOL-39), noun and verb picture naming accuracy Treated and untreated items
There were a number of significant changes at 4 weeks after stimulation Phonemic fluency: significant increase SAQOL-39: significant increases in psychosocial/mood and communication scales Verb naming: significant increases in % named correctly (treated and untreated items) and significant decreases in number of “circumlocution” and “replacement with noun” errors
12, 24, and 48 weeks of phonemic fluency: further increases at 48 weeks SAQOL-39: effects on psychosocial/mood scale maintained at 24 weeks and on communication scale at 48 weeks Verb naming: effects on % named correctly maintained at 48 weeks and effects on error type maintained at 24 weeks
Pilot study 3 single sessions, one week between conditions
None
Scores on a noun and verb naming task (calculated as a function of correct responses without cues and with one/two letter phonological cues)
Naming scores were significantly higher than baseline following anodal left/cathodal right stimulation than following either cathodal left/anodal right or sham stimulation () There was no significant difference between noun and verb naming
N/A
1 month later Experiment 1 20 minutes × 5 days for 2 weeks 9 days between simultaneous and sham
1
30
Severe nonfluent Possible crossed aphasia
None
Scores on the noun and verb naming task
Naming scores were significantly higher than baseline following active than following sham stimulation () There was no significant difference between noun and verb naming
Scores taken every three days after stimulation; effect maintained for 9 days
4 months later Experiment 2 20 minutes × 5 days for 2 weeks 9 days between simultaneous and sham
None
Scores on the noun and verb naming tas
There was no significant difference in naming scores following active or sham stimulation There was no significant difference between noun and verb naming
N/A
4 months later Experiment 3 20 minutes × 5 days for 2 weeks 9 days between simultaneous and sham
None
Scores on the noun and verb naming task
Naming scores were significantly higher than baseline following active than following sham stimulation () There was no significant difference between noun and verb naming
Scores taken every three days after stimulation; effect maintained for 6 days
