Mr compatible leads and electrodes

The conditioned stimuli consisted of two Gabor patches (diameter: 8° visual angle; spatial frequency: 2.1 Hz with randomized spatial phase; contrast ratio: 0.75): one oriented 45° from the horizontal (which was referred to as the 'rightward' oriented patch) and one oriented 135° from the horizontal (which was referred to as the 'leftward' oriented patch). Whenever a
Gabor was presented it flashed on and off at a rate of 2Hz (1,750ms on, 250ms off) with a random spatial phase to avoid adaptation [85] . We chose to use Gabor stimuli as previous research demonstrated that they are sensitive to the effects of emotion [86] and they can be decoded from early visual cortex when being imagined [33] . The unconditioned stimulus (US) consisted of a 500ms (at 50Hz) mild electric shock delivered to the fingertips of the ring and pinky fingers of the left hand [13] , administered using E13-22 (Coulbourn Instruments, Allentown, PA), and included MR-compatible leads and electrodes (BIOPAC systems, CA), and a grounded RF filter. The schedule of stimulus presentation was delivered with Psychtoolbox-3 [87, 88] in MATLAB (MathWorks, Natick, MA, USA). The auditory instructions were created from www.fromtexttospeech.com (language: US English, Voice: Heather, Speed: medium) and delivered using Sensimetric MRI-compatible Insert Earphones [89] .