The Role of Different Prefrontal Areas in Visual Metacognition

Not Applicable

Completed

Conditions: Healthy

Interventions: Other: Transcranial magnetic stimulation

Registration Number: NCT04263766

Lead Sponsor: Georgia Institute of Technology

Brief 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.

Recruitment & Eligibility

Status: COMPLETED

Sex: All

Target Recruitment: 76

Inclusion Criteria

right-handed
adults 18-40
with normal or corrected-to-normal vision

Exclusion Criteria

history of seizures
family history of epilepsy
stroke
severe headaches
metal anywhere in the head (excluding the mouth)
cardiac pacemakers
current use of medication for neurological or psychiatric conditions

Study & Design

Study Type: INTERVENTIONAL

Study Design: SINGLE_GROUP

Arm && Interventions

Group	Intervention	Description
Healthy Adult Volunteers	Transcranial magnetic stimulation	The experiment has a within-subject design where each subject will receive TMS to different brain areas. The analysis will involve comparing the effects of TMS to different regions.

Primary Outcome Measures

Name	Time	Method
Average Confidence Difference With the 0 ms Condition	6 months	The average confidence difference for each delay condition and the 0 ms condition for each group (DLPFC or vertex). Confidence was self-reported together with the decision on a 4-point scale with the minimum score being one (not confident at all) and the highest score being four (very confident). The range of the scale is 1 (not confident at all) to 4 (very confident).
Average Mratio Difference With the 0 ms Condition	6 month	The average Mratio difference for each delay condition and the 0 ms condition for each group (DLPFC or vertex). The Mratio is derived from signal detection theoretical modeling of the observer's decision and confidence response. It is the ratio of two measures: the observer's metacognitive sensitivity (meta-d', the ability to discriminate between correct and incorrect responses) and the observer's stimulus sensitivity (d', the ability to discriminate between the two stimulus classes). The Mratio could be calculated from subjects' self-rated confidence together with task performance.

Secondary Outcome Measures