Abstract
BackgroundExtinction-based procedures are often used to inhibit maladaptive fear responses. However, because extinction procedures show efficacy limitations, transcranial direct current stimulation (tDCS) has been suggested as a promising add-on enhancer.ObjectiveIn this study, we tested how cathodal tDCS over the right dorsolateral prefrontal cortex affects extinction and tried to unveil the processes at play that boost the effectiveness of extinction procedures and its translational potential to the treatment of anxiety disorders.MethodsWe implemented a fear conditioning paradigm whereby 41 healthy women (mean age = 20.51 ± 5.0) were assigned to either cathodal tDCS (n = 27) or sham tDCS (n = 16). Fear responses were measured with self-reports, autonomic responses, and implicit avoidance tendencies.ResultsCathodal tDCS shows no statistically significant effect in extinction, according to self-reports, and seems to even negatively affect fear conditioned skin conductance responses. However, one to three months after the tDCS session and extinction, we found a group difference in the action tendencies towards the neutral stimuli (F (1, 41) = 12.04, p = .001, ηp2 = .227), with the cathodal tDCS group (as opposed to the sham group) showing a safety learning (a positive bias towards the CS-), with a moderate effect size. This suggests that cathodal tDCS may foster stimuli discrimination, leading to a decreased generalization effect.DiscussionCathodal tDCS may have enhanced long-term distinctiveness between threatening cues and perceptively similar neutral cues through a disambiguation process of the value of the neutral stimuli—a therapeutic target in anxiety disorders. Future studies should confirm these results and extend the study of cathodal tDCS effect on short term avoidance tendencies.
Highlights
According to the classical fear conditioning model of anxiety disorders, anxiety- and fearrelated responses are the result of associative learning processes, whereby threatening experiences are associated with originally neutral stimuli that subsequently take on anxiety-inducing properties
The modulatory assumptions are that transcranial direct current stimulation (tDCS) 1) induces cortical excitability and neuroplasticity, modulating long-term potentiation (LTP) and longterm depression (LTD) mechanisms [6,7]; 2) its effects are polarity specific [8,9] in that anodal stimulation is excitatory, whereas cathodal stimulation is inhibitory when stimulating motor or parietal regions but inconsistent in other brain regions [10]; 3) it interferes with the cortical and subcortical regions involved in fear learning networks and their connectivity patterns [11,12]; and 4) its effects may persist over time [13,14]
This study aims to verify if cathodal tDCS leads to the extinction of the conditioned fear response, achieved through a reduced participation of the PFC which is putatively associated to the disruption of reconsolidation processes [30,31] or Cathodal tDCS effect in fear extinction if, on the contrary, cathodal tDCS hinders the extinction of the conditioned fear response [30,31]
Summary
Extinction-based procedures are often used to inhibit maladaptive fear responses. Because extinction procedures show efficacy limitations, transcranial direct current stimulation (tDCS) has been suggested as a promising add-on enhancer. Editor: Peter Schwenkreis, BG-Universitatsklinikum Bergmannsheil, Ruhr-Universitat Bochum, GERMANY. Data Availability Statement: All relevant data are available in the Open Science Framework repository at https://osf.io/rmnq3/?view_only= 1a9110a2a178453789df74c885a995b6.
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