To fullfill the objectives of this application, a generalization paradigm has been designed and psychophysiologically validated in which 6 rings presented on a computer screen gradually increase in size. For half of participants the smallest ring is the conditioned stimulus paired with electric shock (CS+) and the largest is the unpaired stimulus (CS-), and for the other half of participants this is reversed. Activity in fear-related brain structures measured via fMRI are predicted to gradually decrease as the presented stimulus gradually becomes less similar to the CS+, forming a generalization slope or gradient. One central hypothesis of the current application is that DCS (Seromycin) will dose dependently increase the steepness of generalization gradients (i.e., reduce fear generalization). This study will include 3 groups of healthy adults recieving either 1) 500 mg Seromycin, 2) 250 mg Seromycin, or placebo only prior to acquisition of fear conditioning. Twenty four hours later, participants will return to complete an fMRI during which brain responses to the danger cue and stimuli resembling the danger cue will be assessed.
