Working MemoryNCT04680481

Non-Invasive Brain Stimulation to Control Large-Scale Brain Networks

A study testing Transcranial alternating current stimulation in people with Working Memory, run by University of Minnesota at 1 site in United States.

Completed

Finished. The study has ended and is not enrolling. Results may be posted on the official record.

Official record

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Trial summary

This project will assess the feasibility of traveling wave transcranial alternating current stimulation (tACS) to modify working memory performance and large-scale brain connectivity in surgical epilepsy patients. Read more about this study

Who is it for?: Ages 18 years and older
Conditions the study is for: Working Memory
What is being tested?: Transcranial alternating current stimulation
Type of treatment: Medical device
Could I receive a placebo?: No, everyone receives an active treatment
How many people: 11 participants
Where: 1 siteUnited States
Study dates: 1 Nov 2020to 1 Sep 2025
Phase: Interventional
Are there results?: Yes, posted in the registrySummary in the doctors' view

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

Ages 18 years and older
All sexes
No healthy volunteers
Adult, Older adult

Who may be able to join

the patient can consent for themselves;
the patient has or is scheduled for surgically implanted electrodes for the purposes of phase II epilepsy surgical evaluation;
age 18+ years old;

Who cannot join

1. diminished capacity to consent;

Trial locations and contacts

1 site in 1 country.

United States1 site

University of Minnesota
Minneapolis, Minnesota, 55455

Other trials in United States

About this study

Official title: Traveling Wave Transcranial Alternating Current Stimulation for the Control of Large-Scale Brain Networks

Conditions: Working Memory
Being tested: Transcranial alternating current stimulation

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

Transcranial alternating current stimulationDevice
Traveling wave transcranial alternating current stimulation will be applied at 4 Hz and 23 Hz over frontal and parietal brain areas in a randomized counterbalanced order.

Study groups in NCT04680481
Study group	Role	What they receive
Posterior-to-Anterior Theta (4 Hz)	Experimental	Participants will experience traveling-wave transcranial alternating current stimulation over the fronto-parietal regions at 4 Hz (theta condition), configured to produce a posterior-to-anterior propagation direction. Receives: Device: Transcranial alternating current stimulation
Anterior-to-Posterior Theta (4 Hz)	Experimental	Participants will experience traveling-wave transcranial alternating current stimulation over the fronto-parietal regions at 4 Hz (theta condition), configured to produce an anterior-to-posterior propagation direction. Receives: Device: Transcranial alternating current stimulation
Posterior-to-Anterior Beta (23 Hz)	Experimental	Participants will experience traveling-wave transcranial alternating current stimulation over the fronto-parietal regions at 23 Hz (beta condition), configured to produce a posterior-to-anterior propagation direction. Receives: Device: Transcranial alternating current stimulation
Anterior-to-Posterior Beta (23 Hz)	Experimental	Participants will experience traveling-wave transcranial alternating current stimulation over the fronto-parietal regions at 23 Hz (beta condition), configured to produce an anterior-to-posterior propagation direction. Receives: Device: Transcranial alternating current stimulation

What is being measured

The primary outcome is the main question the study is designed to answer.

Post/Pre Theta Power Ratio
Ratio of post-cue to pre-cue theta-band (4-8 Hz) power during the working-memory task under each traveling-wave tACS condition. Pre-cue theta power was calculated from -0.60 to -0.10 seconds relative to cue onset, and post-cue theta power was calculated from 0.20 to 0.80 seconds. A ratio of 1 indicates no change in theta power following the cue; values greater than 1 indicate increased post-cue theta power, and values below 1 indicate decreased post-cue theta power.
Measured: During each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.
Working Memory Accuracy
Proportion of correct responses during the n-back working-memory task under each traveling-wave tACS condition. Higher values indicate greater response accuracy.
Measured: During each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.
Reaction Time During Working Memory Task
Mean reaction time, in seconds, for behavioral responses during the n-back working-memory task under each traveling-wave tACS condition. Lower values indicate faster responses, whereas higher values indicate slower responses.
Measured: During each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.

Secondary outcomes (3)

Evidence Accumulation Rate (Drift Rate, v)
Drift rate (v) was estimated from accuracy, mean reaction time, and reaction-time variance during the n-back working-memory task using the EZ-diffusion decision model (EZ-DDM). Drift rate represents the rate of evidence accumulation toward a decision boundary. Higher positive values indicate faster evidence accumulation, whereas lower values indicate slower evidence accumulation. Drift rate was not constrained to a predefined numerical range. The reported values are unitless model parameter estimates.
Measured: Derived from behavioral performance during each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.
EZ-Diffusion Decision Model Boundary Separation
Boundary separation (a) was estimated from accuracy, mean reaction time, and reaction-time variance during the n-back working-memory task using the EZ-diffusion decision model (EZ-DDM). Boundary separation represents the amount of evidence required before making a response. Higher values indicate a greater amount of evidence required and a more conservative decision threshold, whereas lower values indicate a lower amount of evidence required and a less conservative decision threshold. Boundary separation was not constrained to a predefined numerical range. The reported values are unitless model parameter estimates.
Measured: Derived from behavioral performance during each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.
EZ-Diffusion Decision Model Non-decision Time
Non-decision time (Ter) was estimated from accuracy, mean reaction time, and reaction-time variance during the n-back working-memory task using the EZ-diffusion decision model (EZ-DDM). Non-decision time represents the estimated time, in seconds, associated with processes outside the evidence-accumulation decision process, including stimulus encoding and response execution. Higher values indicate longer non-decision processing time, whereas lower values indicate shorter non-decision processing time.
Measured: Derived from behavioral performance during each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

1 Nov 20201 Sep 2025

First posted23 Dec 2020
Study start1 Nov 2020
Primary completion1 Sep 2025
Study completion1 Sep 2025

Resources

Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
Posted resultsParticipant flow, outcome measures and adverse events reported by the sponsor.
Other trials for Working MemoryStudies of the same condition, open and under way.
What the trial phases meanHow a treatment moves from first tests in people to approval.

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design

Study type: Interventional
Phase: Phase N/A
Primary purpose: Basic science
Allocation: Randomised
Intervention model: Crossover
Masking: Single blind
Who is masked: Participant
Enrolment: 11 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT04680481
Sponsor's protocol ID: STUDY00004009
Other IDs: RF1MH124909
Status last verified: Oct 2026
First submitted: 14 Dec 2020
Last updated: 27 Oct 2026
Results posted: Yes, on ClinicalTrials.gov
FDA-regulated drug: No
FDA-regulated device: Yes
Individual data sharing: Yes: De-identified data will be shared following the IRB guidelines and Data Sharing Policy for the National Institute of Mental Health (NOT-MH-19-033).

Want to know more?

The sponsor has not listed a contact. The official record may have more details.

Talk to your doctor first and take this page with you. Only the study team can confirm whether you can join.

Questions to ask the study team

What is the study trying to find out?
What would I need to do, and how often would I visit?
Could I receive a placebo instead of the treatment?
What are the possible risks and benefits for me?
Will it cost me anything? Are travel or time paid for?
Can I keep seeing my own doctor during the study?
What happens when the study ends?

See locations

Recruiting
tACS for Working Memory in Schizophrenia
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Strengthening Neuro-Cognitive Skills for Success in School, Work and Beyond
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RecruitingPhase 2
Cross-over Study on the Influence of Fampridine on Working Memory in Mild to Moderate Depression
Working Memory, Mild to Moderate Depression
Not yet recruiting
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Mental Fatigue, Cognitive Performance
RecruitingPhase 4
A Study Testing How Well the Drug Extract of Ginkgo Biloba Leaves Tablets Works for People With Memory or Thinking Problems After a Stroke When Added to Standard Treatment
Ischemic Stroke Hospitalized, Impairment, Cognitive

All Working Memory trials

Study at a glance

From the registry record, last updated by the sponsor on 27 Oct 2026. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: Traveling Wave Transcranial Alternating Current Stimulation for the Control of Large-Scale Brain Networks
ClinicalTrials.gov ID: NCT04680481
Acronym / sponsor ID: STUDY00004009
Conditions: Working Memory
Study type: Interventional
Recruitment status: Completed
Enrolment: 11 participants (actual)
Lead sponsor: University of MinnesotaUniversity, hospital or other
Collaborators: National Institute of Mental Health (NIMH)
Study start: 1 Nov 2020 (actual)
Primary completion: 1 Sep 2025 (actual)
Study completion: 1 Sep 2025 (actual)
First posted: 23 Dec 2020 (actual)
Results: Posted 27 Oct 2026

Clinical summary

The research question as the sponsor registered it. This describes what the study plans to test, not what it found.

Study design

Primary purpose: Basic science
Allocation: Randomised
Intervention model: Crossover
Masking: Single blind (participant)
Number of arms: 4

Arm	Type	Receives
Posterior-to-Anterior Theta (4 Hz)	Experimental	Device: Transcranial alternating current stimulationParticipants will experience traveling-wave transcranial alternating current stimulation over the fronto-parietal regions at 4 Hz (theta condition), configured to produce a posterior-to-anterior propagation direction.
Anterior-to-Posterior Theta (4 Hz)	Experimental	Device: Transcranial alternating current stimulationParticipants will experience traveling-wave transcranial alternating current stimulation over the fronto-parietal regions at 4 Hz (theta condition), configured to produce an anterior-to-posterior propagation direction.
Posterior-to-Anterior Beta (23 Hz)	Experimental	Device: Transcranial alternating current stimulationParticipants will experience traveling-wave transcranial alternating current stimulation over the fronto-parietal regions at 23 Hz (beta condition), configured to produce a posterior-to-anterior propagation direction.
Anterior-to-Posterior Beta (23 Hz)	Experimental	Device: Transcranial alternating current stimulationParticipants will experience traveling-wave transcranial alternating current stimulation over the fronto-parietal regions at 23 Hz (beta condition), configured to produce an anterior-to-posterior propagation direction.

Who may qualify

Ages: 18 years and older
Sex: All
Healthy volunteers: Not accepted
Age groups: Adult, Older adult

Key inclusion criteria (3 listed)

the patient can consent for themselves;
the patient has or is scheduled for surgically implanted electrodes for the purposes of phase II epilepsy surgical evaluation;
age 18+ years old;

Key exclusion criteria (1 listed)

1. diminished capacity to consent;

Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.

Interventions

Intervention	Type	Arms
Transcranial alternating current stimulationTraveling wave transcranial alternating current stimulation will be applied at 4 Hz and 23 Hz over frontal and parietal brain areas in a randomized counterbalanced order.	Device	Anterior-to-Posterior Beta (23 Hz), Anterior-to-Posterior Theta (4 Hz), Posterior-to-Anterior Beta (23 Hz), Posterior-to-Anterior Theta (4 Hz)

Primary outcome

Post/Pre Theta Power Ratio
Time frame: During each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.
Ratio of post-cue to pre-cue theta-band (4-8 Hz) power during the working-memory task under each traveling-wave tACS condition. Pre-cue theta power was calculated from -0.60 to -0.10 seconds relative to cue onset, and post-cue theta power was calculated from 0.20 to 0.80 seconds. A ratio of 1 indicates no change in theta power following the cue; values greater than 1 indicate increased post-cue theta power, and values below 1 indicate decreased post-cue theta power.
Working Memory Accuracy
Time frame: During each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.
Proportion of correct responses during the n-back working-memory task under each traveling-wave tACS condition. Higher values indicate greater response accuracy.
Reaction Time During Working Memory Task
Time frame: During each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.
Mean reaction time, in seconds, for behavioral responses during the n-back working-memory task under each traveling-wave tACS condition. Lower values indicate faster responses, whereas higher values indicate slower responses.

3 secondary outcomes

Evidence Accumulation Rate (Drift Rate, v)
Time frame: Derived from behavioral performance during each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.
EZ-Diffusion Decision Model Boundary Separation
Time frame: Derived from behavioral performance during each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.
EZ-Diffusion Decision Model Non-decision Time
Time frame: Derived from behavioral performance during each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.

Results and safety

Results posted to the registry on 27 Oct 2026, as reported by the sponsor. Figures are copied from the record, not re-analysed. Full results on ClinicalTrials.gov.

Participant flow

Group	Started	Completed
All Participants	11	6

Primary outcome: Post/Pre Theta Power Ratio

Time frame: During each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.. Mean (Standard Deviation). Unit: ratio

Measure	4 Hz Anterior to Posterior n = 8	4 Hz Posterior to Anterior n = 7	23 Hz Anterior to Posterior n = 5	23 Hz Posterior to Anterior n = 6
Value	0.9828 (0.0052)	0.9855 (0.0034)	0.5749 (0.031)	0.5125 (0.061)

Population analysed: Participants were enrolled in a within-subject crossover study and could receive more than one stimulation condition. Not all participants completed every stimulation condition. The number analyzed reflects participants with usable outcome data for each condition: 4 Hz Anterior to Posterior, n=8; 4 Hz Posterior to Anterior, n=7; 23 Hz Anterior to Posterior, n=5; and 23 Hz Posterior to Anterior, n=6.

Primary outcome: Working Memory Accuracy

Time frame: During each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.. Mean (Standard Deviation). Unit: Proportion correct

Measure	4 Hz Anterior to Posterior n = 8	4 Hz Posterior to Anterior n = 7	23 Hz Anterior to Posterior n = 5	23 Hz Posterior to Anterior n = 6
Value	0.7918 (0.0659)	0.8519 (0.0562)	0.8419 (0.0518)	0.8184 (0.0916)

Primary outcome: Reaction Time During Working Memory Task

Time frame: During each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.. Mean (Standard Deviation). Unit: Seconds

Measure	4 Hz Anterior to Posterior n = 8	4 Hz Posterior to Anterior n = 7	23 Hz Anterior to Posterior n = 5	23 Hz Posterior to Anterior n = 6
Value	0.713 (0.0828)	0.7746 (0.0871)	0.7178 (0.164)	0.7062 (0.1278)

3 secondary outcomes are reported in the full results.

Adverse events

Time frame: Adverse events were assessed during and immediately following each stimulation session. Participants at risk are reported by stimulation condition and reflect the number of participants who received each condition: 4 Hz Anterior to Posterior, n=8; 4 Hz Posterior to Anterior, n=7; 23 Hz Anterior to Posterior, n=5; and 23 Hz Posterior to Anterior, n=6.. Other adverse events reported at 0% frequency or more

Group	Serious adverse events	Other adverse events	Deaths
4 Hz Anterior to Posterior	0 of 8 (0%)	0 of 8 (0%)	0 of 8
4 Hz Posterior to Anterior	0 of 7 (0%)	0 of 7 (0%)	0 of 7
23 Hz Anterior to Posterior	0 of 5 (0%)	0 of 5 (0%)	0 of 5
23 Hz Posterior to Anterior	0 of 6 (0%)	0 of 6 (0%)	0 of 6

Limitations and caveats (from the sponsor): This exploratory study involved a small sample of patients with epilepsy undergoing intracranial monitoring. Clinical and logistical constraints prevented some participants from completing all stimulation conditions, resulting in unequal sample sizes. The small sample and incomplete data may limit statistical power and generalizability; however, the study provides rare intracranial electrophysiological data combined with noninvasive brain stimulation.

Loading the posted results from ClinicalTrials.gov…

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 27 Oct 2026.
Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
Individual participant dataSharing planned: Yes. De-identified data will be shared following the IRB guidelines and Data Sharing Policy for the National Institute of Mental Health (NOT-MH-19-033).

Related trials for Working Memory

Recruiting
tACS for Working Memory in Schizophrenia
Schizophrenia, Working Memory
Recruiting
Strengthening Neuro-Cognitive Skills for Success in School, Work and Beyond
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RecruitingPhase 2
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Not yet recruiting
Predicting Declines in Attention and Memory During a Prolonged Mental Task
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RecruitingPhase 4
A Study Testing How Well the Drug Extract of Ginkgo Biloba Leaves Tablets Works for People With Memory or Thinking Problems After a Stroke When Added to Standard Treatment
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Referral and contact

AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.

Alexander Opitz, PhD principal investigator

University of Minnesota

1 site in 1 country: see every site and its status.

Questions about this trial

What is this clinical trial studying?

A study testing Transcranial alternating current stimulation in people with Working Memory, run by University of Minnesota at 1 site in United States.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 3 inclusion and 1 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: finished, as of the sponsor's last update on 27 Oct 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 1 site in United States. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

Are results available for this study?

Yes. Results are posted in the registry (first posted 27 Oct 2026). A summary is in the For doctors view, and the full results are on ClinicalTrials.gov.

How can a doctor refer a patient or contact the research team?

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Post/Pre Theta Power Ratio (time frame: During each working-memory task performed concurrently with tACS, approximately 5 minutes per stimulation session.). The study lists 3 primary outcomes in all. It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT04680481.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 27 Oct 2026.