The effect of left frontal transcranial direct-current stimulation on propranolol-induced fear memory acquisition and consolidation deficits

Accumulating evidence supports the efficacy of transcranial direct current stimulation (tDCS) in modulating numerous cognitive functions. Despite the fact that tDCS has been used for the enhancement of memory and cognition, very few animal studies have addressed its impact on the modulation of fear memory. This study was designed to determine whether pre/post-training frontal tDCS application would alter fear memory acquisition and/or consolidation deficits induced by propranolol in NMRI mice. Results indicated that administration of β1-adrenoceptor blocker propranolol (0.1 mg/kg) impaired fear memory retrieval. Pre/post-training application of anodal tDCS when propranolol was administered prior to training reversed contextual memory retrieval whereas only the anodal application prior to training could induce the same result in the auditory test. Meanwhile, anodal stimulation had no effect on fear memories by itself. Moreover, regardless of when cathode was applied and propranolol administered, their combination restored contextual memory retrieval, while only cathodal stimulation prior to training facilitated the contextual memory retrieval. Also, auditory memory retrieval was restored when cathodal stimulation and propranolol occurred prior to training but it was abolished when stimulation occurred after training and propranolol was administered prior to training. Collectively, our findings show that tDCS applied on the left frontal cortex of mice affects fear memory performance. This alteration seems to be task-dependent and varies depending on the nature and timing of the stimulation. In certain conditions, tDCS reverses the effect of propranolol. These results provide initial evidence to support the timely use of tDCS for the modulation of fear-related memories.