The Role of Different Prefrontal Areas in Visual Metacognition
Condition: Healthy
Study type: Interventional

Summary: 
      The study will use transcranial magnetic stimulation (TMS) to investigate the causal role of
      different brain regions during visual perception. TMS is a well-established technique used by
      hundreds of labs in the world. The risks associated with the technique are well understood
      and can be minimized by strict adherence to established safety guidelines. In the proposed
      study, the investigators will use TMS to specifically address the topic of how metacognitive
      evaluation is supported by the two prefrontal areas: the dorsolateral prefrontal cortex
      (DLPFC) and the anterior prefrontal cortex (aPFC). The data will be collected from healthy
      adults and will ultimately deepen the investigator's understanding of the mechanisms behind
      the normal processes related to confidence generation and metacognition.
    

Detailed description: 
      Participants will complete a task on visual perception and receive TMS in order to assess
      which regions of the brain are important for confidence generation in perceptual tasks. The
      task will involve judging the identity of visual stimuli (oriented black-and-white gratings)
      and providing a confidence rating on the judgment that they performed.

      The researchers will deliver TMS to several brain regions such as the anterior prefrontal
      cortex (aPFC), dorsolateral prefrontal cortex (DLPFC), and a control site. The researchers
      will then investigate participants' accuracy and confidence levels depending on where TMS was
      delivered. The researchers expect that aPFC TMS will decrease the metacognitive sensitivity
      of the participants, whereas DLPFC TMS will decrease their average confidence level. TMS will
      be delivered time locked to the onset of the stimulus and the researchers will investigate
      what is the critical period of involvement of a given region.

      The TMS protocol is well within the established safety limits. Participants will be required
      to fill out screening and demographic forms delivered at the Center for Advanced Brain
      Imaging (CABI). In order to dose appropriately the TMS stimulation, it is necessary to
      perform motor threshold determination. Motor threshold (MT) is defined as the minimum
      magnetic flux needed to elicit a visual hand twitch (in the contralateral first dorsal
      interosseus muscle). MT is the standard in the field for determining the intensity of TMS for
      each individual to reduce seizure risk. The scalp region producing the largest hand twitch
      will be identified. At that scalp location, the lowest TMS intensity able to elicit 5 visible
      twitches in 10 trials at this site will be determined. Individual MT will be used to
      determine the intensity of stimulation for each individual, as recommended by safety
      guidelines. This procedure usually takes about 5 minutes and also serves the purpose of
      acquainting participants to TMS stimulation. In this study, the researchers will use
      intensities between 100 and 120% of MT, even though the safety guidelines allow for
      stimulation intensities of at least 130% of MT.
    

Intervention name(s): Transcranial magnetic stimulation
Intervention type(s): Other
Intervention description(s): TMS will be delivered to different brain areas in order to establish their contribution to visual metacognition.
Intervention model: Single Group Assignment
Intervention model description: TMS manipulation. Within-subjects design. Each participant will receive TMS to three different sites: DLPFC, aPFC, and a control site.
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Transcranial Magnetic Stimulation; Metacognition; Prefrontal Cortex