Healthy
Conditions
Keywords
Transcranial Magnetic Stimulation, Metacognition, Prefrontal Cortex
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.
Interventions
OTHERTranscranial magnetic stimulation
TMS will be delivered to different brain areas in order to establish their contribution to visual metacognition.
Sponsors
National Institute of Mental Health (NIMH)
Georgia Institute of Technology
Study design
Allocation
NA
Intervention model
SINGLE_GROUP
Primary purpose
BASIC_SCIENCE
Masking
NONE
Intervention model description
TMS manipulation. Within-subjects design. Each participant will receive TMS to three different sites: DLPFC, aPFC, and a control site.
Eligibility
Sex/Gender
ALL
Age
18 Years to 40 Years
Healthy volunteers
Yes
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
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| 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. |
Countries
United States
Participant flow
Participants by arm
| Arm | Count |
|---|---|
| DLPFC Group The experiment has a within-subject design where each subject will receive TMS (Transcranial magnetic stimulation) at DLPFC at different time point (0 ms, 200 ms, 300 ms, 400 ms, 500 ms) after the stimulus presentation in order to reveal the timing of confidence computation in DLPFC. | 50 |
| Vertex Group The experiment has a within-subject design where each subject will receive TMS (Transcranial magnetic stimulation) at vertex at different time point (0 ms, 200 ms, 300 ms, 400 ms, 500 ms) after the stimulus presentation in order to reveal the timing of confidence computation in DLPFC. | 26 |
| Total | 76 |
Withdrawals & dropouts
| Period | Reason | FG000 | FG001 |
|---|---|---|---|
| Overall Study | Lack of Efficacy | 1 | 3 |
| Overall Study | Withdrawal by Subject | 6 | 4 |
Baseline characteristics
| Characteristic | DLPFC Group | Total | Vertex Group |
|---|---|---|---|
| Age, Continuous | 20.75 years STANDARD_DEVIATION 1.81 | 20.86 years STANDARD_DEVIATION 2.61 | 20.96 years STANDARD_DEVIATION 10.18 |
| Race (NIH/OMB) American Indian or Alaska Native | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) Asian | 32 Participants | 48 Participants | 16 Participants |
| Race (NIH/OMB) Black or African American | 3 Participants | 4 Participants | 1 Participants |
| Race (NIH/OMB) More than one race | 1 Participants | 1 Participants | 0 Participants |
| Race (NIH/OMB) Native Hawaiian or Other Pacific Islander | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) Unknown or Not Reported | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) White | 14 Participants | 23 Participants | 9 Participants |
| Region of Enrollment United States | 50 participants | 76 participants | 26 participants |
| Sex: Female, Male Female | 23 Participants | 35 Participants | 12 Participants |
| Sex: Female, Male Male | 27 Participants | 41 Participants | 14 Participants |
Adverse events
| Event type | EG000 affected / at risk | EG001 affected / at risk |
|---|---|---|
| deaths Total, all-cause mortality | 0 / 50 | 0 / 26 |
| other Total, other adverse events | 0 / 50 | 0 / 26 |
| serious Total, serious adverse events | 0 / 50 | 0 / 26 |
Outcome results
Primary
Average Confidence Difference With the 0 ms Condition
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).
Time frame: 6 months
Population: The analysis population is after the exclusion of subjects who have their 0 ms condition accuracy 3.5% lower than the average accuracy of all delay conditions
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| DLPFC-200 ms | Average Confidence Difference With the 0 ms Condition | 0.14 score on a scale (1-4) | Standard Deviation 0.15 |
| DLPFC-300 ms | Average Confidence Difference With the 0 ms Condition | 0.14 score on a scale (1-4) | Standard Deviation 0.15 |
| DLPFC-400 ms | Average Confidence Difference With the 0 ms Condition | 0.14 score on a scale (1-4) | Standard Deviation 0.14 |
| DLPFC-500 ms | Average Confidence Difference With the 0 ms Condition | 0.15 score on a scale (1-4) | Standard Deviation 0.17 |
| Vertex-200 ms | Average Confidence Difference With the 0 ms Condition | -0.01 score on a scale (1-4) | Standard Deviation 0.05 |
| Vertex-300 ms | Average Confidence Difference With the 0 ms Condition | -0.04 score on a scale (1-4) | Standard Deviation 0.08 |
| Vertex-400 ms | Average Confidence Difference With the 0 ms Condition | -0.04 score on a scale (1-4) | Standard Deviation 0.1 |
| Vertex-500 ms | Average Confidence Difference With the 0 ms Condition | -0.04 score on a scale (1-4) | Standard Deviation 0.11 |
Comparison: Our null hypothesis is TMS to DLPFC would not lead to a significant change in confidence across all 4 delay conditions compared to TMS to the vertex.p-value: <0.001t-test, 2 sided
p-value: 0.99ANOVA
p-value: 0.83ANOVA
Primary
Average Mratio Difference With the 0 ms Condition
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.
Time frame: 6 month
Population: The analysis population is after the exclusion of subjects whose 0 ms condition accuracy is 3.5% lower than the average accuracy of all four delay conditions.
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| DLPFC-200 ms | Average Mratio Difference With the 0 ms Condition | 0.014 Ratio | Standard Deviation 0.959 |
| DLPFC-300 ms | Average Mratio Difference With the 0 ms Condition | 0.087 Ratio | Standard Deviation 0.429 |
| DLPFC-400 ms | Average Mratio Difference With the 0 ms Condition | 0.043 Ratio | Standard Deviation 0.586 |
| DLPFC-500 ms | Average Mratio Difference With the 0 ms Condition | 0.070 Ratio | Standard Deviation 0.467 |
| Vertex-200 ms | Average Mratio Difference With the 0 ms Condition | -0.211 Ratio | Standard Deviation 0.453 |
| Vertex-300 ms | Average Mratio Difference With the 0 ms Condition | -0.170 Ratio | Standard Deviation 0.436 |
| Vertex-400 ms | Average Mratio Difference With the 0 ms Condition | 0.043 Ratio | Standard Deviation 0.386 |
| Vertex-500 ms | Average Mratio Difference With the 0 ms Condition | 0.077 Ratio | Standard Deviation 0.432 |
Comparison: Our null hypothesis is TMS to DLPFC would not lead to a significant change in Mratio across all 4 delay conditions compared to TMS to the vertex.p-value: >0.19ANOVA