Criticality, Working Memory, and Effort

Study Results

Results pending

The study team has not published outcome measurements, participant flow, or safety data for this trial yet. Check back later for updates.

Basic Information

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Recruitment Status

COMPLETED

Clinical Phase

NA

Total Enrollment

30 participants

Study Classification

INTERVENTIONAL

Study Start Date

2023-03-15

Study Completion Date

2023-06-30

Brief Summary

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The project examines electroencephalography, MRI, and behavioral measures indexing flexibility (critical state dynamics) in the brain when healthy young adults do demanding cognitive tasks, and in response to transcranial magnetic stimulation.

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Detailed Description

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The healthy human brain is a complex, dynamical system which is hypothesized to lie near a phase transition at rest - at the boundary between order and chaos. Proximity to this critical point is functionally adaptive as it affords maximal flexibility, dynamic range, and information handling capacity, with implications for working memory function. Divergence from this critical point has become correlated with diverse forms of psychopathology and neuropathy suggesting that distance from a critical point is both a potential biomarker of disorder and also a target for intervention in disordered brains. The Investigators have further hypothesized that subjective cognitive effort is a reflection of sub-criticality induced by engagement with demanding tasks.

A key control parameter determining distance from criticality in a resting brain is hypothesized to be the balance of cortical excitation to inhibition (the "E/I balance"). Transcranial magnetic stimulation is a widely used experimental and clinical tool for neuromodulation and theta-burst stimulation (TBS) protocols are thought to modulate the E/I balance. Here the Investigators test whether cortical dynamics can be systematically modulated away from the critical point with continuous theta-burst stimulation (cTBS), which is thought to decrease the E/I balance, and thereby impact on working memory function and subjective cognitive effort during performance of the working memory tasks.

Conditions

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Healthy

Study Design

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Allocation Method

NA

Intervention Model

SINGLE_GROUP

The study will involve two sessions of within-subject, sham-controlled continuous theta burst stimulation delivered either at the left dorsolateral prefrontal cortex or angular gyrus.

Primary Study Purpose

BASIC_SCIENCE

Blinding Strategy

NONE

The specific session that a participant is in will be known to the experimenter (there is no way for the experimenter not to know since they are administering stimulation). To mitigate the impact on participants, they will be instructed that the brain will be stimulated on two different days, making no reference to possible differential effects across brain regions. The experimental condition will not be explained to the participant until the end of their participation, during debriefing.

Study Groups

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Transcranial magnetic stimulation participants

All participants will be recruited into a single arm where, across two sessions they will receive transcranial magnetic stimulation in separate session to either the dorsolateral prefrontal cortex or the angular gyrus. Session order will be counter-balanced across participants, and stimulation target will be blinded to the participants until after their participation is complete.

Group Type EXPERIMENTAL

transcranial magnetic stimulation

Intervention Type DEVICE

The study intervention is modulation of cortical excitation to inhibition (E/I) balance in the dorsolateral prefrontal cortex (dlPFC) by means of 2 trains of spaced continuous theta burst stimulation (cTBS) using a transcranial magnetic stimulation device. As prior work (Huang et al 2005; Chung et al. 2018) has shown that cTBS reliably decreases the cortical E/I ratio with diverse cortical targets, the Investigators expect to replicate a reduction in E/I balance when applied. The mechanism of action is thought to be an increase in inhibitory neurotransmission across diverse timescales. The endpoint of this stimulation will be a decrease in the local E/I ratio that should last at least 60 minutes post-stimulation (Chung et al., 2018).

In separate sessions, all participants will receive stimulation to either the dorsolateral prefrontal cortex (dlPFC) or to the angular gyrus (AG). The Investigators will contrast the effects of dlPFC cTBS with control cTBS to the AG.

Interventions

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transcranial magnetic stimulation

The study intervention is modulation of cortical excitation to inhibition (E/I) balance in the dorsolateral prefrontal cortex (dlPFC) by means of 2 trains of spaced continuous theta burst stimulation (cTBS) using a transcranial magnetic stimulation device. As prior work (Huang et al 2005; Chung et al. 2018) has shown that cTBS reliably decreases the cortical E/I ratio with diverse cortical targets, the Investigators expect to replicate a reduction in E/I balance when applied. The mechanism of action is thought to be an increase in inhibitory neurotransmission across diverse timescales. The endpoint of this stimulation will be a decrease in the local E/I ratio that should last at least 60 minutes post-stimulation (Chung et al., 2018).

In separate sessions, all participants will receive stimulation to either the dorsolateral prefrontal cortex (dlPFC) or to the angular gyrus (AG). The Investigators will contrast the effects of dlPFC cTBS with control cTBS to the AG.

Intervention Type DEVICE

Eligibility Criteria

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Inclusion Criteria

1. Provision of signed and dated informed consent form
2. Stated willingness to comply with all study and availability for the duration of the study
3. Males and females; Ages 18-45
4. Healthy, neurologically normal with no diagnosed mental or physical illness
5. Willingness to adhere to the MRI and two session stimulation protocol
6. Fluent in English
7. Normal or corrected to normal vision
8. At least twelve years of education (high school equivalent)
9. Right-handed

Exclusion Criteria

1. Ongoing drug or alcohol abuse
2. Diagnosed psychiatric or mental illness
3. Currently taking psychoactive medication
4. Prior brain injury
5. Metal in body
6. History of seizures or diagnosis of epilepsy
7. Claustrophobia
8. Pregnant or possibly pregnant
9. Younger than 18 or older than 45
10. Use of medications which potentially lower the usage threshold

Minimum Eligible Age

18 Years

Maximum Eligible Age

45 Years

Eligible Sex

ALL

Accepts Healthy Volunteers

Yes