Waking up an Exhausted Brain: The Effects of Cognitive Fatigue on Fear Memory Generalization and Its Modulation by Glucose and Vagus Nerve Stimulation.

Anxiety disorders are costly to both individuals and society and yet, despite their prevalence and impact, the causal mechanisms are poorly understood. Predisposing factors (e.g., genetics) certainly contribute, as do learning processes such as generalization (i.e., making the same response to similar stimuli). The latter is likely sensitive to situational factors such as mental fatigue that impair memory, as poorer memory for a stimulus is more likely to produce a generalized response. However, the degree to which mental fatigue affects fear generalization is unknown. My goal is to address this question and contribute to our understanding of anxiety. I will also seek to eliminate the effects of mental fatigue on fear generalization through the administration of glucose. Past research has observed that glucose, but not a placebo, can replenish mental fatigue. It may have such an effect because it provides energy to the brain. However, there is evidence that energy transfer is not necessary, and that the activation of the vagus nerve, which is involved in digestion, is sufficient. The proposed research will explore this possibility using a transcutaneous electrical nerve stimulator to replenish fatigue. The replenishing ability of vagal activation will be further investigated through a nutrient manipulation where fatty acid solutions that are equated in energy, similarly metabolized, but that differentially activate the vagus nerve are administered to depleted participants.