Unilateral Prefrontal Direct Current Stimulation Effects are Modulated by Working Memory Load and Gender

The Gonda Multidisciplinary Brain Research Center, Bar Ilan University, Ramat Gan, Israel.
Brain Stimulation (Impact Factor: 5.43). 06/2012; 6(3). DOI: 10.1016/j.brs.2012.05.014
Source: PubMed

ABSTRACT BACKGROUND: Recent studies revealed that anodal transcranial direct current stimulation (tDCS) to the left dorsolateral prefrontal cortex (DLPFC) may improve verbal working memory (WM) performance in humans. In the present study, we evaluated executive attention, which is the core of WM capacity, considered to be significantly involved in tasks that require active maintenance of memory representations in interference-rich conditions, and is highly dependent on DLPFC function. OBJECTIVES: We investigated verbal WM accuracy using a WM task that is highly sensitive to executive attention function. We were interested in how verbal WM accuracy may be affected by WM load, unilateral DLPFC stimulation, and gender, as previous studies showed gender-dependent brain activation during verbal WM tasks. METHODS: We utilized a modified verbal n-Back task hypothesized to increase demands on executive attention. We examined "online" WM performance while participants received transcranial direct current stimulation (tDCS), and implicit learning performance in a post-stimulation WM task. RESULTS: Significant lateralized "online" stimulation effects were found only in the highest WM load condition revealing that males benefit from left DLPFC stimulation, while females benefit from right DLPFC stimulation. High WM load performance in the left DLPFC stimulation was significantly related to post-stimulation recall performance. CONCLUSIONS: Our findings support the idea that lateralized stimulation effects in high verbal WM load may be gender-dependent. Further, our post-stimulation results support the idea that increased left hemisphere activity may be important for encoding verbal information into episodic memory as well as for facilitating retrieval of context-specific targets from semantic memory.

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Available from: Oded Meiron, Feb 10, 2015
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    • "The results also show that the effects of tDCS are highly variable and may be dependent upon the task and stimulation parameters, as illustrated in studies probing working memory function. For instance, working memory was shown to be enhanced by cathodal tDCS over the left DLPFC [29], anodal tDCS over the left DLPFC [21,41e49]; and anodal tDCS over the right DLPFC [48]. Working memory performance was also shown to be decreased by cathodal tDCS over the left DLPFC [21], anodal tDCS over the left DLPFC [36]; and tDCS over bilateral DLPFC (left anodal/ right cathodal: [62]). "
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    ABSTRACT: Background Transcranial direct current stimulation (tDCS) is increasingly used in research and clinical settings, and the dorsolateral prefrontal cortex (DLPFC) is often chosen as a target for stimulation. While numerous studies report modulation of cognitive abilities following DLPFC stimulation, the wide array of cognitive functions that can be modulated makes it difficult to predict its precise outcome. Objective The present review aims at identifying and characterizing the various cognitive domains affected by tDCS over DLPFC. Methods Articles using tDCS over DLPFC indexed in PubMed and published between 2000 and January 2014 were included in the present review. Results tDCS over DLPFC affects a wide array of cognitive functions, with sometimes apparent conflicting results. Conclusion Prefrontal tDCS has the potential to modulate numerous cognitive functions simultaneously, but to properly interpret the results, a clear a priori hypothesis is necessary, careful technical consideration are mandatory, further insights into the neurobiological impact of tDCS are needed, and consideration should be given to the possibility that some behavioral effects may be partly explained by parallel modulation of related functions.
    Brain Stimulation 10/2014; 7(6). DOI:10.1016/j.brs.2014.10.003 · 5.43 Impact Factor
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    • "The speed measure also showed benefits of a left ventral PFC anode (F9), insofar as that group performed better than the other groups, except for C4. We speculate that the working memory load associated with retaining and updating memory of “foe” mines from game to game may have benefited from stimulation of left PFC, previously found to benefit working memory (e.g., Hoy et al., 2013; Meiron and Lavidor, 2013). However, both left and right PFC stimulation at F3 and F4 have been found to have other effects, e.g., more cautious driving in a simulator (Beeli et al., 2008) and reduced risk taking (Fecteau et al., 2007). "
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    ABSTRACT: There is a need to facilitate acquisition of real world cognitive multi-tasks that require long periods of training (e.g., air traffic control, intelligence analysis, medicine). Non-invasive brain stimulation-specifically transcranial Direct Current Stimulation (tDCS)-has promise as a method to speed multi-task training. We hypothesized that during acquisition of the complex multi-task Space Fortress, subtasks that require focused attention on ship control would benefit from tDCS aimed at the dorsal attention network while subtasks that require redirection of attention would benefit from tDCS aimed at the right hemisphere ventral attention network. We compared effects of 30 min prefrontal and parietal stimulation to right and left hemispheres on subtask performance during the first 45 min of training. The strongest effects both overall and for ship flying (control and velocity subtasks) were seen with a right parietal (C4, reference to left shoulder) montage, shown by modeling to induce an electric field that includes nodes in both dorsal and ventral attention networks. This is consistent with the re-orienting hypothesis that the ventral attention network is activated along with the dorsal attention network if a new, task-relevant event occurs while visuospatial attention is focused (Corbetta et al., 2008). No effects were seen with anodes over sites that stimulated only dorsal (C3) or only ventral (F10) attention networks. The speed subtask (update memory for symbols) benefited from an F9 anode over left prefrontal cortex. These results argue for development of tDCS as a training aid in real world settings where multi-tasking is critical.
    Frontiers in Human Neuroscience 09/2014; 8:665. DOI:10.3389/fnhum.2014.00665 · 2.90 Impact Factor
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    • "Twelve participants were in the active bilateral condition, and 12 participants were in the sham condition. We employed a between subject design because repetition of the same working memory paradigm in a within-subject design may facilitate learning effects related to improved response-selection strategies (Meiron and Lavidor, 2013). All participants fulfilled the following inclusion criteria: right-handed, normal/corrected to normal vision, healthy and free of medication. "
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    ABSTRACT: We intended to examine how theta-rhythm transcranial alternating current stimulation (tACS) (versus sham non-active stimulation) modulated associations between working memory accuracy and later retrospective self-evaluation scores. Healthy participants were required to complete a verbal working memory task while receiving tACS bilaterally over the dorsolateral prefrontal cortex (DLPFC) versus sham DLPFC stimulation. After completion of the online and post-stimulation working memory tasks, participants were asked to rate the level of success-confidence on the two preceding working memory tasks. As expected, online working memory accuracy was improved in the active bilateral DLPFC condition versus sham stimulation. Importantly, this working memory enhancement was related to post-stimulation self-evaluation scores. Theoretically, our findings indicated that cognitive-control representations (e.g., working memory accuracy) could serve as the optimal frame of reference for later retrospective metacognitive judgments. Noninvasive application of bi-frontal oscillatory currents might enhance functional connectivity between prefrontal regulatory components of working memory and retrospective monitoring in humans. Importantly, along with recent electrophysiological finding indicating interaction of tACS with ongoing oscillatory activity, our preliminary findings support the feasibility of utilizing tACS to treat theta-rhythm functional disconnectivity and related cognitive impairments in schizophrenia.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 07/2013; 125(1). DOI:10.1016/j.clinph.2013.06.013 · 2.98 Impact Factor
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