Treating Traumatic Brain Injury With Transcranial Direct Current Stimulation

Change in Selective attention and cognitive flexibility as assessed by the Attention Network Task (ANT)

This will be measured using the Attention Network Task (ANT). An efficiency score for executive attention is derived by comparing scores on trials with congruent flankers to trials with incongruent flankers. Subjects will tend to be slower and less accurate for incongruent trials, the size of the difference indicates the extent to which an individual can supress conflicting response tendencies. A larger difference between congruent and incongruent trials score indicates a lower executive efficiency (score range: 0-96)..

Change in attention and task switching as assessed by the N-Back score

The N-back task is a well-established task that assesses working memory and working memory capacity. Participants are presented with words in sequence and instructed to reply whether the current word matches the one presented 2 words ago (2-back). Scoring will be based on the total number of correct responses (hit rate) minus the number of incorrect responses (false alarm rate), where a greater score is better (score range: 0-80).

Change in Self-Ordered Pointing Task (SOPT)

The SOPT is a test used to assess executive functioning. In this task, participants are shown a series of pages, each displaying the same set of abstract images arranged in a random order. On each page, the participant must point to one image, ensuring not to select the same image more than once across the entire series. A correct response involves selecting a previously un-chosen image, while an error is recorded when a participant selects an image already chosen on a previous page. Performance will be measured by total number of errors measured out of the total number of possible responses, with a higher error count indicating greater impairment.

Change in attention and task switching as assessed by the Trail Making Task

This will be measured using Trail Making Task and N-Back scores. The Trail Making Test is scored by time. Participants are allowed 0 - 300 seconds to complete the task. Less time needed to complete the task is indicative of better task-switching.

Change in Digit Span Forward

Digit span forward involves the recall of a series of single digits (sets of 1-8 digits) in the same order the digits were presented. Scoring is based on the number of digits or blocks shown in a trial (i.e. 1,7 is 2 digits). There are two trials for each span, if both trials are correct the score is a whole number (i.e. 2). If one trial is incorrect in a span, subtract 0.5 from that tier (i.e. 1.5). A higher number is considered better. (Score range for forward tasks: 0-9)

Change in Digit Span Backward

This will be measured using Digit Span Backward for verbal working memory and spatial span Backward for spatial working memory. The digit span backward is a well-established task that assesses rote immediate verbal memory and working memory. Participants are presented with a series of digits and are instructed to repeat the digits in the reverse order. Scoring is based on the number of digits shown in a trial (i.e. 1,7 is 2 digits). There are two trials for each span, if both trials are correct the score is a whole number (i.e. 2). If one trial is incorrect in a span, subtract 0.5 from that tier (i.e. 1.5). A higher number is considered better. (Score range for backwards tasks: 0-8)

Change in attention and inhibition as assessed by the Simon Task

This will be measured using Simon test scores. The Simon task assesses an individual's ability to flexibly shift the perceptual focus in response to changing demands, particularly the participant's capacity to inhibit a habitual response in favor of an unconventional one. Performance on the Simon task is typically scored based on measures such as reaction time and accuracy. Increased reaction times and higher error rates on incongruent trials are indicative of greater difficulty in inhibiting the interference caused by the word's meaning, reflecting decreased cognitive flexibility and inhibition abilities (accuracy score range: 0-120).

Change in Global Cognitive Scores as assessed by the Montreal Cognitive Assessment (MoCA)

This will be measured using the Montreal Cognitive Assessment (MoCA). Scored from 0-30 points, higher is better.

Change in verbal fluency task score

Verbal fluency tasks (semantic and letter fluency) involve generating as many words as possible in one minute. Scoring will be based on number of words generated per minute. The investigators will compute the raw score of items correct and compute change in outcome between baseline and each time point. Increase in score is considered benefit.

Change in semantic content of connected speech

Using the Cookie Theft image from the Boston Diagnostic Aphasia Examination (BDAE) investigators will obtain representative language samples as participants describe the images. The investigators will compute the raw score of items (semantics) correct and transform to percent correct (range: 0-100%), computing change in outcome in percent difference between before intervention and each time point after. Increase in score is considered a benefit.

Change in spelling as assessed by the Johns Hopkins Dysgraphia battery

Accuracy in spelling using the Johns Hopkins Dysgraphia battery will be compared for tDCS and sham conditions. The investigators will compute the raw score of items correct using a spelling scoring system accounting for additions, substitutions, and deletions. Each word will get a score from 0-1 and the average of pseudowords and real words will be computed and transformed to percent correct (range: 0-100%), computing change in outcome in percent difference before intervention and each time point after. Increase in score is considered a benefit.