Causal Role of the Aperiodic Signal for Working Memory

Florida State University30 enrolled

Overview

Working memory (WM) is the ability to hold relevant information in mind in the absence of sensory input. The capacity for WM is a foundation for cognitive control and higher cognitive function more broadly. Previous research demonstrated that during the delay period of WM tasks, oscillatory electrical activity in the prefrontal cortex in the theta-frequency band (4-8 Hz) increased in amplitude. However, other groups found that the slope of the aperiodic signal in the brain was positively correlated with individual differences in WM capacity. Since low-frequency power and a steeper slope of the aperiodic signal are confounded in many analyses, it is not clear whether the slope of the aperiodic signal or the amplitude of low-frequency oscillations underlie WM capacity. With many studies investigating the causal role of theta oscillations in WM, the purpose of this project is to investigate the role of the aperiodic signal in WM performance.

The experiment comprises two experimental sessions. The first session serves as a baseline session where electroencephalography (EEG) is recorded during working memory (WM) task performance. The difficulty of the task is titrated to the individual participant and they are familiarized with the task. In the second session, the participant receives each type of transcranial random aperiodic stimulation (tRAS): steep-tRAS, flat-tRAS, sham-tRAS. Stimulation is delivered in one of these three waveforms for each block while the participant performs the WM task. The type of stimulation that is received is balanced, randomized, and intermixed by block. This study is double-blinded such that the participant and the researcher are not aware of what type of stimulation is being delivered. Each block is approximately 5 minutes and twelve total blocks are collected with stimulation. The type of tRAS for that block (steep-tRAS, flat-tRAS, or sham-tRAS) is started just prior to the beginning of the task block and ramps down at the end of the task block. For each task block, the tRAS takes 15 seconds to ramp up at the beginning and 15 seconds to ramp down at the conclusion of the task block. In total, the participant receives approximately 60 minutes of stimulation, which is approximately 20 minutes of each type of stimulation. Following each task block, participants stare at a fixation cross and relax without stimulation. This "resting-state" EEG recording is used to assess the aftereffects of tRAS on brain activity. The first session will take 2 hours to complete and the second session will take 3 hours to complete.

Study Type

INTERVENTIONAL

Interventions

Steep-tRASDEVICE

Stimulation will be delivered via the NeuroConn Direct Current Stimulator Plus Multiple Channels, an investigational electrical non-invasive brain stimulation device that is being used for foundational neuroscience and translational research.

Flat-tRASDEVICE

Sham-tRASDEVICE

Eligibility

Sex: ALLMin age: 18 YearsMax age: 35 YearsHealthy volunteers:

Medical Language ↔ Plain English

Inclusion Criteria: * Between the ages of 18 and 35 * Able to provide informed consent * Normal or corrected-to-normal vision * Willing to comply with all study procedures and be available for the duration of the study * Ability to speak, read and understand English without a translator * Not color-blind Exclusion Criteria: * ADHD/ADD (currently under treatment) * Neurological disorder and conditions * Medical or neurological illness or treatment for a medical disorder that could interfere with study participation, e.g., unstable cardiac disease, HIV/AIDS, malignancy, liver or renal impairment * Prior brain surgery * Any brain devices/implants, including cochlear implants and aneurysm clips * History of traumatic brain injury * (For females) Pregnant * Anything that, in the opinion of the investigator, would place the participant at increased risk or preclude the participant's full compliance with or completion of the study * Current use of medications know to produce specific EEG activity known to disrupt interpretations of the findings including but not limited to: benzodiazepines, antipsychotics, antiepileptics and central nervous system stimulants

Outcomes

Primary Outcomes

Change in number of remembered items

The number of remembered items, often referred to as working memory capacity, is calculated as the number of items to be remembered multiplied by the number of items successfully remembered divided by the number of total trials. The range of values is 0 to 7 where a larger number denotes a greater number of items that were remembered.

Time frame: 3 hours

Secondary Outcomes

Change in slope of the power spectrum of the EEG

The power spectrum of an electrical brain recording is calculated by performing a Fourier transform on the time signal. The slope is calculated as the general trend of this background signal.