No Effect of Cathodal Transcranial Direct Current Stimulation on Fear Memory in Healthy Human Subjects

Abstract

Background: Studies have demonstrated that fear memories can be modified using non-invasive methods. Recently, we demonstrated that anodal transcranial direct current stimulation (tDCS) of the right dorsolateral prefrontal cortex is capable of enhancing fear memories. Here, we examined the effects of cathodal tDCS of the right dorsolateral prefrontal cortex during fear reconsolidation in humans. Methods: Seventeen young, healthy subjects were randomly assigned to two groups, which underwent fear conditioning with mild electric stimuli paired with a visual stimulus. Twenty-four hours later, both groups were shown a reminder of the conditioned fearful stimulus. Shortly thereafter, they received either tDCS (right prefrontal—cathodal, left supraorbital—anodal) for 20 min at 1 mA, or sham stimulation. A day later, fear responses of both groups were compared. Results: On Day 3, during fear response assessment, there were no significant differences between the tDCS and sham group (p > 0.05). Conclusion: We conclude that cathodal tDCS of the right dorsolateral prefrontal cortex (right prefrontal—cathodal, left supraorbital—anodal) did not influence fear memories.

The effect of cathodal tDCS on fear extinction: a cross-measures study

“…Previous literature showed increased vmPFC activity during classical extinction (17) but decreased when extinction occurs within the reconsolidation window (25). Whereas in our study we found that cathodal tDCS putatively occurring during the reconsolidation window, may reduce the fear index/avoidance tendency in the long-term, Mungee et al (21) found no effect for cathodal tDCS in SCRs. Whilst in our study we asked participants to verbally recall the CS+ followed by classical extinction (days 2 and 3), in Mungee et al (21) there was no information update because participants did not go through a complete extinction procedure following tDCS.…”

“…Whereas in our study we found that cathodal tDCS putatively occurring during the reconsolidation window, may reduce the fear index/avoidance tendency in the long-term, Mungee et al (21) found no effect for cathodal tDCS in SCRs. Whilst in our study we asked participants to verbally recall the CS+ followed by classical extinction (days 2 and 3), in Mungee et al (21) there was no information update because participants did not go through a complete extinction procedure following tDCS. However, according to seminal studies, this new information is a necessary condition for the update of the CS+/US association (24).…”

“…Similarly, albeit in laboratory cathodal stimulation of the rDLPFC of healthy subjects, showed no effect in fear extinction (21), two successful case reports found cathodal tDCS therapeutic effects (22,23), where we can see that cathodal stimulation may be a promising tool in alleviating anxiety symptoms. One possible explanation for the dissonant results between experimental studies and case reports comes from the different mechanisms that may be at play, whether extinction occurs inside or outside the reconsolidation time window.…”

“…Also, Abend et al (20) suggested that cathodal stimulation may have a long-term depression effect over the medial PFC during the reconsolidation window, potentially eading to enhanced extinction. However, when Mungee et al (21) used cathodal tDCS after fear recall (aimed at triggering reconsolidation), no impact was found on Skin Conductance Responses (SCRs). Of note, in their study, participants went through cathodal tDCS immediately after recall (a single presentation of the CS+), and the authors did not employ a fear extinction procedure, during which new information is thought to support the update of the fear memory trace, and to putatively lead to the persistent elimination of the conditioned fear response (27).…”

Offline tDCS modulates prefrontal-cortical-subcortical-cerebellar fear pathways in delayed fear extinction

“…hyper-vigilance and excessive worrying). Thus, to eliminate the consolidated CR, extinction (the translational equivalent to exposure-based therapies) is implemented, consisting of consecutive presentations of the CS+ alone, leading to a new learning that inhibits the CS+/US association (18).By delivering tDCS to the right or left DLPFC to enhance fear extinction, researchers aimed to artificially modulate brain activity and decrease the fear response (19)(20)(21)(22). Counterintuitively, whereas previous studies have shown that tDCS using the anode electrode over the DLPFC leads to decreased fear, this gain was also associated with the adverse effect of decreasing stimuli discrimination (21,23).…”