Abstract
Introduction Cognitive control (CC) over emotion implies the ability to pursue internal goals even in the presence of conflicting stimuli. Evidence from depression describe a loss of CC and hypoactivity of the dorsolateral prefrontal cortex (DLPFC) as causal factors (1).Transcranial direct current stimulation (tDCS) is a save and reliable stimulation technique that modulates cortical excitability. Anodal, activity-enhancing tDCS of the left DLPFC ameliorates deficient CC in depression (2). The present study aimed to examine the mechanisms of this effect using parallel Electroencephalography (EEG) and tDCS. The late positive potential (LPP) was used as a neurophysiological signature of attention allocation (3). It was hypothesized that the valence-specific difference amplitude of the LPP would predict the attentional bias as measured in reaction time (RT). Method 87 healthy participants received tDCS over the left DLPFC in one out of four stimulation intensities (0/0.5/1/1.5mA) while performing a delayed working memory task. In this task, participants memorized a string of eight letters and performed a recognition task on a target letter after a delay period in which pictures of either negative or neutral content were shown. EEG was recorded parallel to tDCS. The LPP was scored in an early (250–500ms) and late (500–1000ms) time window. To quantify valence-specific changes in the neural and behavioral domain, a difference measure for both LPP and RT was calculated: Δearly LPP neg-neu and ΔRT neg-neu . Results A significant main effect for valence was found in both the early and late LPP ( p =.05). No significant effect of stimulation ( p >.5) was apparent. A negative correlation appeared between difference values Δearly LPP neg-neu and ΔRT neg-neu – behavioral and neural measures of the CC – in the sham condition ( r =−429, p =.046). However, this correlation progressively disappeared with increased stimulation intensity ( r =.980, p =.020). Discussion This study provides evidence for a close link between a valence specific neural marker, the LPP, and working memory performance under emotional distraction. We propose that the increment in the LPP difference value signifies an increase of valence-specific neural recruitment and thus facilitates task performance (4). Since no systematic distraction by negative pictures (attentional bias) was present in this group of healthy subjects we assume that stimulation did not exert a systematic effect but increasingly interfered with the physiological association between LPP and performance. Future studies within clinical populations will follow to validate the utility of the marker found here.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have