Brain Criticality, Oculomotor Control, and Cognitive 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

RECRUITING

Clinical Phase

NA

Total Enrollment

60 participants

Study Classification

INTERVENTIONAL

Study Start Date

2024-08-01

Study Completion Date

2026-06-01

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 operate, at rest, near a phase transition - at the boundary between order and chaos. Proximity to this critical point is functionally adaptive as it affords maximal flexibility, dynamic range, and information transmission capacity, with implications for short term memory and cognitive control. 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 task performance depends on how closely brains operate to criticality during task performance and also that subjective cognitive effort is a reflection of divergence from 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) and intermittent theta-burst stimulation (iTBS), which is thought to decrease and increase E/I balance, respectively. Depending on baseline E/I balance prior to stimulation, this will make people's brains either operate closer to, or farther away from critiality and thereby impact on cognitive control and subjective cognitive effort during performance of control-demanding tasks.

Conditions

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Healthy

Study Design

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Allocation Method

RANDOMIZED

Intervention Model

CROSSOVER

The study will involve three sessions of within-subject, crossover, double-blind transcranial magnetic stimulation with either 1) active intermittent theta burst stimulation, 2) active continuous theta burst stimulation or 3) sham intermittent or continuous theta burst stimulation.

Primary Study Purpose

BASIC_SCIENCE

Blinding Strategy

DOUBLE

Participants Investigators

Participants numbers will be assigned three blinded codes which are linked with either sham, active continuous, or active intermittent theta burst stimulation in the stimulator protocol. The investigator will enter the code to initiate the corresponding stimulator protocol, but will not know which protocol is active.

Half of participants will be assigned a sham code corresponding to sham continuous theta burst stimulation and half will be assigned a sham code corresponding to sham intermittent theta burst stimulation. So, for any given session, either continuous or intermittent theta burst stimulation will be used, but it will be unclear whether the stimulation is active or sham.

Study Groups

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Continuous theta burst stimulation

In a cross-over design, all participants will, in one session, receive continuous theta burst stimulation, to the right frontal eye field. Session order will be counter-balanced across participants, and stimulation protocol will be blinded to participants and the Investigator until after data collection is complete.

Group Type ACTIVE_COMPARATOR

transcranial magnetic stimulation

Intervention Type DEVICE

The study intervention involves modulation of cortical excitation to inhibition (E/I) balance in the right frontal eye field (FEF) by means of 2 trains of spaced continuous or intermittent theta burst stimulation (cTBS, iTBS, respectively) using a transcranial magnetic stimulation device. The endpoint of this stimulation will be a decrease (cTBS) or increase (iTBS) in the local E/I ratio that should last at least 60 minutes post-stimulation (Chung et al., 2016).

In separate sessions, all participants will receive either active or stimulation to the FEF. The Investigators will contrast the effects of both iTBS and cTBS to sham stimulation and to each other.

Intermittent theta burst stimulation

In a cross-over design, all participants will, in one session, receive intermittent theta burst stimulation, to the right frontal eye field. Session order will be counter-balanced across participants, and stimulation protocol will be blinded to participants and the Investigator until after data collection is complete.

Group Type ACTIVE_COMPARATOR

transcranial magnetic stimulation

Intervention Type DEVICE

The study intervention involves modulation of cortical excitation to inhibition (E/I) balance in the right frontal eye field (FEF) by means of 2 trains of spaced continuous or intermittent theta burst stimulation (cTBS, iTBS, respectively) using a transcranial magnetic stimulation device. The endpoint of this stimulation will be a decrease (cTBS) or increase (iTBS) in the local E/I ratio that should last at least 60 minutes post-stimulation (Chung et al., 2016).

In separate sessions, all participants will receive either active or stimulation to the FEF. The Investigators will contrast the effects of both iTBS and cTBS to sham stimulation and to each other.

Sham theta burst stimulation

In a cross-over design, all participants will, in one session, receive sham theta burst stimulation, to the right frontal eye field. Session order will be counter-balanced across participants, and stimulation protocol will be blinded to participants and the Investigator until after data collection is complete.

Group Type SHAM_COMPARATOR

transcranial magnetic stimulation

Intervention Type DEVICE

The study intervention involves modulation of cortical excitation to inhibition (E/I) balance in the right frontal eye field (FEF) by means of 2 trains of spaced continuous or intermittent theta burst stimulation (cTBS, iTBS, respectively) using a transcranial magnetic stimulation device. The endpoint of this stimulation will be a decrease (cTBS) or increase (iTBS) in the local E/I ratio that should last at least 60 minutes post-stimulation (Chung et al., 2016).

In separate sessions, all participants will receive either active or stimulation to the FEF. The Investigators will contrast the effects of both iTBS and cTBS to sham stimulation and to each other.

Interventions

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transcranial magnetic stimulation

The study intervention involves modulation of cortical excitation to inhibition (E/I) balance in the right frontal eye field (FEF) by means of 2 trains of spaced continuous or intermittent theta burst stimulation (cTBS, iTBS, respectively) using a transcranial magnetic stimulation device. The endpoint of this stimulation will be a decrease (cTBS) or increase (iTBS) in the local E/I ratio that should last at least 60 minutes post-stimulation (Chung et al., 2016).

In separate sessions, all participants will receive either active or stimulation to the FEF. The Investigators will contrast the effects of both iTBS and cTBS to sham stimulation and to each other.

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)

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