Overview
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.
Description
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.
Eligibility
Inclusion Criteria:
- Provision of signed and dated informed consent form
- Stated willingness to comply with all study and availability for the duration of the study
- Males and females; Ages 18-45
- Healthy, neurologically normal with no diagnosed mental or physical illness
- Willingness to adhere to the MRI and two session stimulation protocol
- Fluent in English
- Normal or corrected to normal vision
- At least twelve years of education (high school equivalent)
Exclusion Criteria:
- Ongoing drug or alcohol abuse
- Diagnosed psychiatric or mental illness
- Currently taking psychoactive medication
- Prior brain injury
- Metal in body
- History of seizures or diagnosis of epilepsy
- Claustrophobia
- Pregnant or possibly pregnant
- Younger than 18 or older than 45
- Use of medications which potentially lower the usage threshold