Effect of Frontal Transcranial Direct Current Stimulation on Word Fluency in Healthy Adults
Havela, Riikka (2020)
2020
Lääketieteen lisensiaatin tutkinto - Licentiate of Medicine
Lääketieteen ja terveysteknologian tiedekunta - Faculty of Medicine and Health Technology
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Hyväksymispäivämäärä
2020-03-17
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202003072587
https://urn.fi/URN:NBN:fi:tuni-202003072587
Tiivistelmä
Introduction: Transcranial direct current stimulation (tDCS) is a noninvasive and well tolerated method for stimulating the brain in a subthreshold manner. It has shown some promise e.g. in treatment of major depressive disorder. The prefrontal cortex is an interesting target for tDCS studies, since the executive functions it performs are compromised in many diseases of the brain. Verbal fluency tasks are one way of measuring executive functions, albeit inherently being a combined task that measures several other functions, such as verbal ability, as well. In this study, we wanted to explore whether tDCS targeted to the dorsolateral prefrontal cortex influences performance in phonemic and semantic word fluency tasks in healthy adults.
Materials and methods: 23 healthy participants, aged 21-34 years, were randomized into two groups, one receiving active tDCS stimulation and the other one receiving sham stimulation. They performed a one-minute phonemic and semantic fluency test before (session 1) and after (session 2) performing Executive reaction time test, a computer-based test engaging several executive functions simultaneously, during which the active or sham stimulation was administered. The number of words produced during the verbal fluency tests was analyzed for the full one-minute test period, and in 15 second intervals using analysis of variance and Student’s T-test.
Results: The semantic fluency task proved to be easier for the participants, as expected. There was also a tendency to perform better in session 2 (post-stimulation) than session 1 (pre-stimulation) in both fluency tasks and in both active and sham stimulation groups, implying learning. Interestingly, there was a statistically significant difference in the semantic fluency test session 2 (post-stimulation) second quarter (15-30 s from the beginning of the test) between the number of words produced by the active and sham stimulation groups with those having received tDCS producing more words.
Conclusions: The results indicate significant learning in repeated verbal fluency tasks influencing the assessment of an intervention on executive functions. tDCS improved verbal fluency in the second quarter of the fluency test. We speculate based on the exponential decay curve of performance in the fluency task that the second quarter is most dependent on executive functions, and thus subtle alterations in executive functions may be more easily detected during this quarter. This is in contrast to the first quarter that relies on semiautomatic access of frequent words rather than effortful retrieval of infrequent words. Furthermore, it may be that in the third and fourth quarter vocabulary may be the limiting factor on the performance rather than the efficiency of executive functions. Thus, while caution is warranted and these preliminary results should be confirmed in future studies, it is possible that there was a subtle improvement in executive functions due to tDCS that was observed only in the second quarter of the fluency task.
Materials and methods: 23 healthy participants, aged 21-34 years, were randomized into two groups, one receiving active tDCS stimulation and the other one receiving sham stimulation. They performed a one-minute phonemic and semantic fluency test before (session 1) and after (session 2) performing Executive reaction time test, a computer-based test engaging several executive functions simultaneously, during which the active or sham stimulation was administered. The number of words produced during the verbal fluency tests was analyzed for the full one-minute test period, and in 15 second intervals using analysis of variance and Student’s T-test.
Results: The semantic fluency task proved to be easier for the participants, as expected. There was also a tendency to perform better in session 2 (post-stimulation) than session 1 (pre-stimulation) in both fluency tasks and in both active and sham stimulation groups, implying learning. Interestingly, there was a statistically significant difference in the semantic fluency test session 2 (post-stimulation) second quarter (15-30 s from the beginning of the test) between the number of words produced by the active and sham stimulation groups with those having received tDCS producing more words.
Conclusions: The results indicate significant learning in repeated verbal fluency tasks influencing the assessment of an intervention on executive functions. tDCS improved verbal fluency in the second quarter of the fluency test. We speculate based on the exponential decay curve of performance in the fluency task that the second quarter is most dependent on executive functions, and thus subtle alterations in executive functions may be more easily detected during this quarter. This is in contrast to the first quarter that relies on semiautomatic access of frequent words rather than effortful retrieval of infrequent words. Furthermore, it may be that in the third and fourth quarter vocabulary may be the limiting factor on the performance rather than the efficiency of executive functions. Thus, while caution is warranted and these preliminary results should be confirmed in future studies, it is possible that there was a subtle improvement in executive functions due to tDCS that was observed only in the second quarter of the fluency task.