Effects of Continuous Theta Burst Stimulation to the Dorsolateral Prefrontal Cortex in Attention to Emotional Stimuli

The goal of this clinical trial is to examine the differential effect of continuous TBS (cTBS) over the left and right dorsolateral prefrontal cortex (DLPFC) on the facilitation of attention towards emotional (i.e., pleasant and distress-ing) versus neutral stimuli in healthy young adults. The main questions it aims to answer are:

1. To what extend a temporary modulation of DLPFC activity through cTBS influences attentional responses to emotional stimuli?
2. To what extend the effects of cTBS on attentional responses to emotional stimuli differ depending on whether the left or right dorsolateral prefrontal cortex (DLPFC) is stimulated?

Researchers will compare four stimulation conditions: 1) real cTBS on the left DLPFC, 2) real cTBS on the right DLPFC, 3) sham cTBS on the left DLPFC, and 4) sham cTBS on the right DLPFC, to see if participants receiving cTBS over the DLPFC would exhibit faster reaction times to probes replacing pleasant and distressing images, relative to a sham condition.

Participants will receive a short cTBS session (40 seconds), and after that, they will be presented with an emotional dot-probe task (computerized task).

Regarding the cTBS Protocol, coil positioning will be determined using standardized coordinates from the EEG International 10-20 system, with F4 corresponding to the right DLPFC stimulation target and F3 corresponding to the left DLPFC. The location and orientation of each participant's coil placement will be indicated on a nylon cap that participants wore throughout the single stimulation session. A figure-of-eight focal coil (70 mm diameter) will be used. The coil will be held in a fixed position by a mechanical arm and oriented so that the induced electric current flowed in a posterior-anterior direction. Stimulus intensities were set at 70% of active motor threshold (AMT). Each TBS session burst consists of 3 pulses at 50 Hz, with each train being repeated every 200 ms (5 Hz) for 40 seconds (600 pulses).

Regarding the dot-probe task is a common laboratory paradigm used to index attentional bias for emotional stimuli at early stages of information processing. It provides a quick, convenient, and inexpensive index of emotional responsiveness. The emotional pictures version of the task used in the current study presents a series of picture pairs of distressing (e.g., crying child), neutral (e.g., book) and pleasant (e.g., smiling baby) emotional content using images primarily taken from the International Affective Picture System (IAPS). This task consists of 1 block of practice stimuli (12 picture pairs) followed by 3 experi-mental blocks, each containing 12 picture pairs. Each picture presentation had three sequential components: (1) a 500 millisecond image of fixation cross appearing in the center of the screen, (2) a 500 millisecond simultaneous presentation of one of three potential picture pairings: neutral-neutral, pleasant-neutral and distress-neutral, with stimuli centered and located above or below the location of the fixation cross, and (3) a second image of fixation cross appearing in either the top or bottom picture location. Participants will be instructed to respond as fast as they could and after every trial they selected a key on the keyboard that corresponded to the location on the screen (up or down) where the dot-probe appeared. If no key was pressed within 5000 milliseconds, the response will be recorded as incorrect.