Aging, Cognitive Decline, Memory, Sleep, Transcranial Alternating Current Stimulation
Conditions
Brief summary
The purpose of this clinical trial is to investigate the feasibility and efficacy of non-invasive transcranial alternating current stimulation (tACS) at gamma frequency in enhancing memory recall and modulating sleep network dynamics measured by at-home electroencephalography (EEG) in healthy elderly people. Eligible participants will first collect sleep EEG at home for one night to acclimate to the data collection during sleep. Participants are then randomized into first undergoing either tACS at gamma band frequencies (i.e. 40Hz) or tACS at a control frequency (i.e. 21Hz). Stimulation is administered in the lab during a cognitive testing battery that includes memorizing items. After a night of sleep with EEG at home, participants return to the lab the following day to measure memory recall. Recall is performed again after five days. This sequence of encoding during stimulation in the lab, sleep EEG at home for one night, and recall is then repeated for the other stimulation condition about a week later. Participants are wearing an actigraphy wristband throughout the study period.
Interventions
DEVICEGamma transcranial alternating current stimulation
tACS (gamma frequency, 40Hz) during cognitive testing (about 40 minutes duration).
DEVICEControl transcranial alternating current stimulation
tACS (control frequency, 21Hz) during cognitive testing (about 40 minutes duration).
DEVICEEEG headband
At-home, ambulatory, single-channel EEG headband which records brain activity during sleep
DEVICEActigraphy wristband
At-home, ambulatory, wrist-worn accelerometer which records levels of motor activity during the whole day
Sponsors
University of North Carolina, Chapel Hill
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
OTHER
Masking
QUADRUPLE (Subject, Caregiver, Investigator, Outcomes Assessor)
Eligibility
Sex/Gender
ALL
Age
50 Years to No maximum
Healthy volunteers
Yes
Inclusion criteria
* \>50 years old
Exclusion criteria
* Implanted device or metal in head (including cochlear implant or other hearing aid), cardiac pacemaker or any other powered medical device * Known neurological disease from history (epilepsy, sleep disorder (insomnia, sleep apnea, restless legs syndrome, parasomnia), stroke or transitory ischemic attack, cognitive impairment, neurodegenerative disease (for example Alzheimer's disease, Parkinson's disease or amyotrophic lateral sclerosis), immune-mediated disease of the central nervous system, chronic infectious brain disease, brain tumor, traumatic brain injury with loss of consciousness and/or intracranial bleeding, chronic pain with the need for daily analgesic use) * Positive screening for epilepsy (questionnaire) * Pathological Montreal Cognitive Assessment (MoCA \<26/30 points) * Brain surgery in the past (lifetime) * Known psychiatric disorder from history (schizophrenia (lifetime), obsessive compulsive disorder (OCD; lifetime), borderline personality disorder (lifetime), anxiety disorder (lifetime), bipolar disorder (lifetime), psychosis (lifetime), eating disorder (lifetime), depression (within the last three months) * Positive screening for anxiety disorder (GAD-7 ≥10/21 points) or positive screening for depression (PHQ-9 ≥5/27 points) * Known other relevant medical condition from history (moderate to severe chronic obstructive pulmonary disease (COPD), abnormal kidney function (defined as estimated Glomerular Filtration Rate \<60ml/min), current liver disease (defined as hepatitis and/or liver cirrhosis), cancer, diabetes mellitus, cardiac disease (heart failure, myocardial infarct, atrial fibrillation and revascularization - all within the last three months) * Working in night shifts or going to bed after midnight on 3 or more nights per week * Positive screening for sleep disorder (PSQI \>5/21 points) * Psychotropic treatment or illegal drugs (including cannabis) within the last three months * Indication for alcohol use disorder: AUDIT score (Alcohol Use Disorders Identification Test; screening for unhealthy alcohol use) ≥7 for females and for males ≥ 65 years or ≥8 for males \<65 years * Not willing to abstain alcohol at least 24 hours before each study visit * Pregnancy, planned pregnancy, fertility treatment planned or ongoing * Having experienced an adverse event in the past after receiving Transcranial Magnetic Stimulation (TMS) * If, after filling out a questionnaire on the participant's medical history that informs researchers of relevant events that marginally increase the risk of an adverse event occurring during TMS, researchers will exercise their expert judgement to determine whether that participant should be excluded
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Amount of Slow Wave Sleep in Sleep-EEG | Baseline (Day 1) | To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on the amount of slow wave sleep (deep/delta sleep) occuring during the night after the intervention. The amount of slow wave sleep during the first two hours of sleep-EEG will be counted. |
| Verbal Memory at Day 2 | Follow-Up (Day 2) | Participants will memorize 15 words (Rey Auditory Verbal Learning Test) during gamma-tACS or control-tACS. They will be required to recall the words on the day after. The number of correctly remembered words will be recorded. |
| Verbal Memory at Day 5 | Follow-Up (Day 5) | Participants will memorize 15 words (Rey Auditory Verbal Learning Test) during gamma-tACS or control-tACS. They will be required to recall the words after 5 days. The number of correctly remembered words will be recorded. |
| Associative Verbal Memory at Day 1 | Baseline (Day 1) | Participants will memorize 8 word-pairs during gamma-tACS or control-tACS. They will be required to recall the pairs on the same day. The number of correctly remembered word pairs will be recorded. |
| Associative Verbal Memory at Day 2 | Follow-Up (Day 2) | Participants will memorize 8 word-pairs during gamma-tACS or control-tACS. They will be required to recall the pairs on the day after. The number of correctly remembered word pairs will be recorded. |
| Associative Verbal Memory at Day 5 | Follow-Up (Day 5) | Participants will memorize 8 word-pairs during gamma-tACS or control-tACS. They will be required to recall the pairs after 5 days. The number of correctly remembered word pairs will be recorded. |
| Percentage of Participants in Which it is Possible to Obtain at Least 4 Hours EEG Recording | Baseline (Day 1) | To establish feasibility of at-home use of a single-channel EEG device during sleep. This will be considered feasible if the device has been worn for at least 4 hours during the first night for \>/= 80% of participants. |
| Percentage of Participants Who Wear the EEG Device During All Three Nights for at Least 4 Hours | Baseline (Day 1) | To establish acceptability of at-home use of the single-channel EEG device during multiple nights. Acceptability will be considered as given if the device has been worn for at least 4 hours during each of the three nights in \>/=80% of participants. |
| Amount of Sleep Spindles in Sleep-EEG | Baseline (Day 1) | To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on the number of sleep spindles occuring during the night after the intervention. Sleep spindles during the first two hours of sleep-EEG will be counted. A sleep spindle is defined as a train of sinusoidal waves with frequency 11-16 Hz and a duration of at least 0.5 seconds. |
| Percent of Participants Tolerating Cognitive Testing During tACS | Baseline (Day 1) | To establish acceptability of tACS combined with cognitive testing in healthy elderly participants and will be considered acceptable if at least \>/= 80% of participants tolerate the procedure. |
| Verbal Memory at Day 1 | Baseline (Day 1) | Participants will memorize 15 words (Rey Auditory Verbal Learning Test) during gamma-tACS or control-tACS. They will be required to recall the words on the same day. The number of correctly remembered words will be recorded. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Attentional Performance (TAP) | Baseline (Day 1), Follow-Up (Day 2) | To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on subtests of the Test of Attentional Performance (TAP) during and on the day after the intervention. Percentile ranks for the following subtests will be calculated: Alertness (reaction time under two conditions), Go/NoGo (stimuli that require a selective reaction, that is, to react or not to react), Divided Attention (a visual and an auditory task must be processed in parallel), Visual Scanning (a matrix-like arrangement of 5 x 5 stimuli is used, the aim being to detect whether this arrangement includes a critical stimulus or not). |
| Performance in Phonematic Fluency-Correct Words | Baseline (Day 1), Follow-Up (Day 2) | To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on a phonematic fluency-task during 1 minute. The number of correct words will be calculated. |
| Performance in Phonematic Fluency-Perseverations | Baseline (Day 1), Follow-Up (Day 2) | To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on a phonematic fluency-task (i.e. production of words that start with a specific letter) during 1 minute. Number of correct words, number of perseverations and number of rule breaks will be calculated. |
| Performance in Phonematic Fluency-Rule Breaks | Baseline (Day 1), Follow-Up (Day 2) | To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on a phonematic fluency-task during 1 minute. Number of correct words, number of perseverations and number of rule breaks will be calculated. |
| Executive Functioning (Time to Complete Stroop Test) | Baseline (Day 1), Follow-Up (Day 2) | To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on the Stroop Color and Word Test during and on the day after the intervention. Time for test completion and errors will be calculated. Selective attention was evaluated with the Stroop Color Word Interference Test. In the interference portion of this test, the subject identifies the color of ink in which words (red, green, or blue) are printed, requiring the subject to inhibit their natural tendency to read the word. A subject's score is the time taken to identify 50 stimulus items. The time taken to complete the maze is inversely proportional to the cognitive function. |
| Executive Functioning (Trail Making Test) | Baseline (Day 1), Follow-Up (Day 2) | To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on the Trail Making Test (TMT; connecting a set of numbers and numbers and letters as quickly as possible while maintaining accuracy) during and on the day after the intervention. The TMT (Part A and Part B) is a measure of visuomotor processing/sequencing speed. Participants must draw a line connecting numbers in ascending order as quickly as possible. Completion time in seconds is recorded (0-120, where lower scores represent better performance). Completion time of Part B is divided by completion time of Part A (Ratio B/A). |
Other
| Measure | Time frame | Description |
|---|---|---|
| Exploration of a Relationship (Correlation) Between the Amount of Sleep Spindles and Slow Wave Sleep With Recall | Baseline (Day 1), Follow-Up (Day 2) | A relationship is defined as a correlation (Pearson's) between memory recall performance (amount of words recalled) and sleep EEG features (especially spindles, slow waves), i.e., whether better memory recall is associated with more sleep spindles and more slow wave sleep in the night after stimulation. |
| Exploration of a Relationship (Correlation) of Sleep-Wake-Schedule Changes and Type of Stimulation | Baseline (Day 1), Follow-Up (Day 2) | To see whether there is a correlation (Pearson's) between type of stimulation/wearing EEG and the motor activity pattern (measured by actigraphy wristband). |
Countries
United States
Participant flow
Participants by arm
| Arm | Count |
|---|---|
| All Participants Participants who received transcranial alternating current stimulation: tACS. | 11 |
| Total | 11 |
Baseline characteristics
| Characteristic | All Participants |
|---|---|
| Age, Customized >50 Years of Age | 11 Participants |
| Ethnicity (NIH/OMB) Hispanic or Latino | 1 Participants |
| Ethnicity (NIH/OMB) Not Hispanic or Latino | 10 Participants |
| Ethnicity (NIH/OMB) Unknown or Not Reported | 0 Participants |
| Race (NIH/OMB) American Indian or Alaska Native | 0 Participants |
| Race (NIH/OMB) Asian | 0 Participants |
| Race (NIH/OMB) Black or African American | 0 Participants |
| Race (NIH/OMB) More than one race | 0 Participants |
| Race (NIH/OMB) Native Hawaiian or Other Pacific Islander | 0 Participants |
| Race (NIH/OMB) Unknown or Not Reported | 0 Participants |
| Race (NIH/OMB) White | 11 Participants |
| Region of Enrollment United States | 11 Participants |
| Sex: Female, Male Female | 5 Participants |
| Sex: Female, Male Male | 6 Participants |
Adverse events
| Event type | EG000 affected / at risk | EG001 affected / at risk |
|---|---|---|
| deaths Total, all-cause mortality | 0 / 10 | 0 / 11 |
| other Total, other adverse events | 0 / 10 | 0 / 11 |
| serious Total, serious adverse events | 0 / 10 | 0 / 11 |
Outcome results
Primary
Amount of Sleep Spindles in Sleep-EEG
To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on the number of sleep spindles occuring during the night after the intervention. Sleep spindles during the first two hours of sleep-EEG will be counted. A sleep spindle is defined as a train of sinusoidal waves with frequency 11-16 Hz and a duration of at least 0.5 seconds.
Time frame: Baseline (Day 1)
Population: Data were not properly collected for some participants due to technical difficulties.
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| Gamma (40Hz) Stimulation | Amount of Sleep Spindles in Sleep-EEG | 57.6 Number of sleep spindles | Standard Deviation 116 |
| Active Control (21 Hz) Stimulation | Amount of Sleep Spindles in Sleep-EEG | 35.8 Number of sleep spindles | Standard Deviation 64 |
Primary
Amount of Slow Wave Sleep in Sleep-EEG
To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on the amount of slow wave sleep (deep/delta sleep) occuring during the night after the intervention. The amount of slow wave sleep during the first two hours of sleep-EEG will be counted.
Time frame: Baseline (Day 1)
Population: Data were not properly collected for some participants due to technical difficulties.
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| Gamma (40Hz) Stimulation | Amount of Slow Wave Sleep in Sleep-EEG | 25.2 minutes | Standard Deviation 31.2 |
| Active Control (21 Hz) Stimulation | Amount of Slow Wave Sleep in Sleep-EEG | 23.2 minutes | Standard Deviation 23.3 |
Primary
Associative Verbal Memory at Day 1
Participants will memorize 8 word-pairs during gamma-tACS or control-tACS. They will be required to recall the pairs on the same day. The number of correctly remembered word pairs will be recorded.
Time frame: Baseline (Day 1)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| Gamma (40Hz) Stimulation | Associative Verbal Memory at Day 1 | 6.1 Number of word pairs recalled | Standard Deviation 0.6 |
| Active Control (21 Hz) Stimulation | Associative Verbal Memory at Day 1 | 5.7 Number of word pairs recalled | Standard Deviation 1.6 |
Primary
Associative Verbal Memory at Day 2
Participants will memorize 8 word-pairs during gamma-tACS or control-tACS. They will be required to recall the pairs on the day after. The number of correctly remembered word pairs will be recorded.
Time frame: Follow-Up (Day 2)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| Gamma (40Hz) Stimulation | Associative Verbal Memory at Day 2 | 5.9 Number of word pairs recalled | Standard Deviation 0.9 |
| Active Control (21 Hz) Stimulation | Associative Verbal Memory at Day 2 | 4.7 Number of word pairs recalled | Standard Deviation 1.9 |
Primary
Associative Verbal Memory at Day 5
Participants will memorize 8 word-pairs during gamma-tACS or control-tACS. They will be required to recall the pairs after 5 days. The number of correctly remembered word pairs will be recorded.
Time frame: Follow-Up (Day 5)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| Gamma (40Hz) Stimulation | Associative Verbal Memory at Day 5 | 5.9 Number of word pairs recalled | Standard Deviation 1.2 |
| Active Control (21 Hz) Stimulation | Associative Verbal Memory at Day 5 | 5.0 Number of word pairs recalled | Standard Deviation 1.7 |
Primary
Percentage of Participants in Which it is Possible to Obtain at Least 4 Hours EEG Recording
To establish feasibility of at-home use of a single-channel EEG device during sleep. This will be considered feasible if the device has been worn for at least 4 hours during the first night for \>/= 80% of participants.
Time frame: Baseline (Day 1)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Value (NUMBER) |
|---|---|---|
| Gamma (40Hz) Stimulation | Percentage of Participants in Which it is Possible to Obtain at Least 4 Hours EEG Recording | 60 percentage of participants |
| Active Control (21 Hz) Stimulation | Percentage of Participants in Which it is Possible to Obtain at Least 4 Hours EEG Recording | 60 percentage of participants |
Primary
Percentage of Participants Who Wear the EEG Device During All Three Nights for at Least 4 Hours
To establish acceptability of at-home use of the single-channel EEG device during multiple nights. Acceptability will be considered as given if the device has been worn for at least 4 hours during each of the three nights in \>/=80% of participants.
Time frame: Baseline (Day 1)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Value (NUMBER) |
|---|---|---|
| Gamma (40Hz) Stimulation | Percentage of Participants Who Wear the EEG Device During All Three Nights for at Least 4 Hours | 10 percentage of participants |
| Active Control (21 Hz) Stimulation | Percentage of Participants Who Wear the EEG Device During All Three Nights for at Least 4 Hours | 10 percentage of participants |
Primary
Percent of Participants Tolerating Cognitive Testing During tACS
To establish acceptability of tACS combined with cognitive testing in healthy elderly participants and will be considered acceptable if at least \>/= 80% of participants tolerate the procedure.
Time frame: Baseline (Day 1)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Value (NUMBER) |
|---|---|---|
| Gamma (40Hz) Stimulation | Percent of Participants Tolerating Cognitive Testing During tACS | 100 percentage of participants |
| Active Control (21 Hz) Stimulation | Percent of Participants Tolerating Cognitive Testing During tACS | 100 percentage of participants |
Primary
Verbal Memory at Day 1
Participants will memorize 15 words (Rey Auditory Verbal Learning Test) during gamma-tACS or control-tACS. They will be required to recall the words on the same day. The number of correctly remembered words will be recorded.
Time frame: Baseline (Day 1)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| Gamma (40Hz) Stimulation | Verbal Memory at Day 1 | 7.7 Number of words recalled | Standard Deviation 1.7 |
| Active Control (21 Hz) Stimulation | Verbal Memory at Day 1 | 6.9 Number of words recalled | Standard Deviation 2.4 |
Primary
Verbal Memory at Day 2
Participants will memorize 15 words (Rey Auditory Verbal Learning Test) during gamma-tACS or control-tACS. They will be required to recall the words on the day after. The number of correctly remembered words will be recorded.
Time frame: Follow-Up (Day 2)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| Gamma (40Hz) Stimulation | Verbal Memory at Day 2 | 5.7 Number of words recalled | Standard Deviation 1.9 |
| Active Control (21 Hz) Stimulation | Verbal Memory at Day 2 | 5.5 Number of words recalled | Standard Deviation 2.5 |
Primary
Verbal Memory at Day 5
Participants will memorize 15 words (Rey Auditory Verbal Learning Test) during gamma-tACS or control-tACS. They will be required to recall the words after 5 days. The number of correctly remembered words will be recorded.
Time frame: Follow-Up (Day 5)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| Gamma (40Hz) Stimulation | Verbal Memory at Day 5 | 4.1 Number of words recalled | Standard Deviation 2.2 |
| Active Control (21 Hz) Stimulation | Verbal Memory at Day 5 | 3.9 Number of words recalled | Standard Deviation 2.3 |
Secondary
Attentional Performance (TAP)
To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on subtests of the Test of Attentional Performance (TAP) during and on the day after the intervention. Percentile ranks for the following subtests will be calculated: Alertness (reaction time under two conditions), Go/NoGo (stimuli that require a selective reaction, that is, to react or not to react), Divided Attention (a visual and an auditory task must be processed in parallel), Visual Scanning (a matrix-like arrangement of 5 x 5 stimuli is used, the aim being to detect whether this arrangement includes a critical stimulus or not).
Time frame: Baseline (Day 1), Follow-Up (Day 2)
Population: Data are missing for some participants due to technical reasons resulting in data not being saved.
| Arm | Measure | Group | Value (MEAN) | Dispersion |
|---|---|---|---|---|
| Gamma (40Hz) Stimulation | Attentional Performance (TAP) | Baseline (Day 1) Alertness | 31.4 percentile rank | Standard Deviation 26.6 |
| Gamma (40Hz) Stimulation | Attentional Performance (TAP) | Baseline (Day 1) Go/NoGo | 42.8 percentile rank | Standard Deviation 37.2 |
| Gamma (40Hz) Stimulation | Attentional Performance (TAP) | Baseline (Day 1) Divided Attention Acoustic | 26.2 percentile rank | Standard Deviation 31.9 |
| Gamma (40Hz) Stimulation | Attentional Performance (TAP) | Baseline (Day 1) Divided Attention Visual | 42.6 percentile rank | Standard Deviation 28.2 |
| Gamma (40Hz) Stimulation | Attentional Performance (TAP) | Baseline (Day 1) Visual Scanning Critical | 65.0 percentile rank | Standard Deviation 27.4 |
| Gamma (40Hz) Stimulation | Attentional Performance (TAP) | Baseline (Day 1) Visual Scanning Non-Critical | 42.8 percentile rank | Standard Deviation 27.2 |
| Gamma (40Hz) Stimulation | Attentional Performance (TAP) | Follow-Up (Day 2) Alertness | 39.2 percentile rank | Standard Deviation 29.9 |
| Gamma (40Hz) Stimulation | Attentional Performance (TAP) | Follow-Up (Day 2) Go/NoGo | 44.0 percentile rank | Standard Deviation 31.5 |
| Gamma (40Hz) Stimulation | Attentional Performance (TAP) | Follow-Up (Day 2) Divided Attention Acoustic | 24.1 percentile rank | Standard Deviation 25 |
| Gamma (40Hz) Stimulation | Attentional Performance (TAP) | Follow-Up (Day 2) Divided Attention Visual | 48.4 percentile rank | Standard Deviation 28.6 |
| Gamma (40Hz) Stimulation | Attentional Performance (TAP) | Follow-Up (Day 2) Visual Scanning Critical | 72.4 percentile rank | Standard Deviation 29 |
| Gamma (40Hz) Stimulation | Attentional Performance (TAP) | Follow-Up (Day 2) Visual Scanning Non-Critical | 47.8 percentile rank | Standard Deviation 28.8 |
| Active Control (21 Hz) Stimulation | Attentional Performance (TAP) | Follow-Up (Day 2) Visual Scanning Critical | 72.0 percentile rank | Standard Deviation 28.5 |
| Active Control (21 Hz) Stimulation | Attentional Performance (TAP) | Baseline (Day 1) Alertness | 32.3 percentile rank | Standard Deviation 26 |
| Active Control (21 Hz) Stimulation | Attentional Performance (TAP) | Follow-Up (Day 2) Alertness | 36.2 percentile rank | Standard Deviation 31.3 |
| Active Control (21 Hz) Stimulation | Attentional Performance (TAP) | Baseline (Day 1) Go/NoGo | 56.1 percentile rank | Standard Deviation 26.7 |
| Active Control (21 Hz) Stimulation | Attentional Performance (TAP) | Follow-Up (Day 2) Divided Attention Visual | 57.3 percentile rank | Standard Deviation 23.4 |
| Active Control (21 Hz) Stimulation | Attentional Performance (TAP) | Baseline (Day 1) Divided Attention Acoustic | 13.8 percentile rank | Standard Deviation 16.2 |
| Active Control (21 Hz) Stimulation | Attentional Performance (TAP) | Follow-Up (Day 2) Go/NoGo | 47.6 percentile rank | Standard Deviation 35.6 |
| Active Control (21 Hz) Stimulation | Attentional Performance (TAP) | Baseline (Day 1) Divided Attention Visual | 38.4 percentile rank | Standard Deviation 28.1 |
| Active Control (21 Hz) Stimulation | Attentional Performance (TAP) | Follow-Up (Day 2) Visual Scanning Non-Critical | 50.5 percentile rank | Standard Deviation 28.7 |
| Active Control (21 Hz) Stimulation | Attentional Performance (TAP) | Baseline (Day 1) Visual Scanning Critical | 67.0 percentile rank | Standard Deviation 24.5 |
| Active Control (21 Hz) Stimulation | Attentional Performance (TAP) | Follow-Up (Day 2) Divided Attention Acoustic | 19.0 percentile rank | Standard Deviation 20.1 |
| Active Control (21 Hz) Stimulation | Attentional Performance (TAP) | Baseline (Day 1) Visual Scanning Non-Critical | 39.0 percentile rank | Standard Deviation 29.3 |
Secondary
Executive Functioning (Time to Complete Stroop Test)
To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on the Stroop Color and Word Test during and on the day after the intervention. Time for test completion and errors will be calculated. Selective attention was evaluated with the Stroop Color Word Interference Test. In the interference portion of this test, the subject identifies the color of ink in which words (red, green, or blue) are printed, requiring the subject to inhibit their natural tendency to read the word. A subject's score is the time taken to identify 50 stimulus items. The time taken to complete the maze is inversely proportional to the cognitive function.
Time frame: Baseline (Day 1), Follow-Up (Day 2)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Group | Value (MEAN) | Dispersion |
|---|---|---|---|---|
| Gamma (40Hz) Stimulation | Executive Functioning (Time to Complete Stroop Test) | Baseline | 54.5 seconds | Standard Deviation 7.2 |
| Gamma (40Hz) Stimulation | Executive Functioning (Time to Complete Stroop Test) | Follow-Up (Day 2) | 48.5 seconds | Standard Deviation 6.6 |
| Active Control (21 Hz) Stimulation | Executive Functioning (Time to Complete Stroop Test) | Baseline | 58.6 seconds | Standard Deviation 11.5 |
| Active Control (21 Hz) Stimulation | Executive Functioning (Time to Complete Stroop Test) | Follow-Up (Day 2) | 53.2 seconds | Standard Deviation 10.1 |
Secondary
Executive Functioning (Trail Making Test)
To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on the Trail Making Test (TMT; connecting a set of numbers and numbers and letters as quickly as possible while maintaining accuracy) during and on the day after the intervention. The TMT (Part A and Part B) is a measure of visuomotor processing/sequencing speed. Participants must draw a line connecting numbers in ascending order as quickly as possible. Completion time in seconds is recorded (0-120, where lower scores represent better performance). Completion time of Part B is divided by completion time of Part A (Ratio B/A).
Time frame: Baseline (Day 1), Follow-Up (Day 2)
Population: One participant was not exposed to 40 Hz due to their time constraints. Data were missing for another participant.
| Arm | Measure | Group | Value (MEAN) | Dispersion |
|---|---|---|---|---|
| Gamma (40Hz) Stimulation | Executive Functioning (Trail Making Test) | Baseline (Day 1) | 1.7 ratio | Standard Deviation 0.6 |
| Gamma (40Hz) Stimulation | Executive Functioning (Trail Making Test) | Follow-Up (Day 2) | 2.3 ratio | Standard Deviation 0.9 |
| Active Control (21 Hz) Stimulation | Executive Functioning (Trail Making Test) | Baseline (Day 1) | 1.9 ratio | Standard Deviation 0.8 |
| Active Control (21 Hz) Stimulation | Executive Functioning (Trail Making Test) | Follow-Up (Day 2) | 1.9 ratio | Standard Deviation 0.3 |
Secondary
Performance in Phonematic Fluency-Correct Words
To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on a phonematic fluency-task during 1 minute. The number of correct words will be calculated.
Time frame: Baseline (Day 1), Follow-Up (Day 2)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Group | Value (MEAN) | Dispersion |
|---|---|---|---|---|
| Gamma (40Hz) Stimulation | Performance in Phonematic Fluency-Correct Words | Baseline | 46.0 Number of correct words | Standard Deviation 13.3 |
| Gamma (40Hz) Stimulation | Performance in Phonematic Fluency-Correct Words | Follow-Up (Day 2) | 46.9 Number of correct words | Standard Deviation 10.8 |
| Active Control (21 Hz) Stimulation | Performance in Phonematic Fluency-Correct Words | Baseline | 45.5 Number of correct words | Standard Deviation 8.1 |
| Active Control (21 Hz) Stimulation | Performance in Phonematic Fluency-Correct Words | Follow-Up (Day 2) | 47.8 Number of correct words | Standard Deviation 9.7 |
Secondary
Performance in Phonematic Fluency-Perseverations
To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on a phonematic fluency-task (i.e. production of words that start with a specific letter) during 1 minute. Number of correct words, number of perseverations and number of rule breaks will be calculated.
Time frame: Baseline (Day 1), Follow-Up (Day 2)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Group | Value (MEAN) | Dispersion |
|---|---|---|---|---|
| Gamma (40Hz) Stimulation | Performance in Phonematic Fluency-Perseverations | Baseline | 1.5 number of perseverations | Standard Deviation 2.1 |
| Gamma (40Hz) Stimulation | Performance in Phonematic Fluency-Perseverations | Follow-Up (Day 2) | 1.3 number of perseverations | Standard Deviation 1.1 |
| Active Control (21 Hz) Stimulation | Performance in Phonematic Fluency-Perseverations | Baseline | 1.1 number of perseverations | Standard Deviation 1.1 |
| Active Control (21 Hz) Stimulation | Performance in Phonematic Fluency-Perseverations | Follow-Up (Day 2) | 1.1 number of perseverations | Standard Deviation 1.9 |
Secondary
Performance in Phonematic Fluency-Rule Breaks
To investigate the effect of a single session of gamma-tACS (compared to control-tACS) on a phonematic fluency-task during 1 minute. Number of correct words, number of perseverations and number of rule breaks will be calculated.
Time frame: Baseline (Day 1), Follow-Up (Day 2)
Population: One participant was not exposed to 40 Hz due to their time constraints.
| Arm | Measure | Group | Value (MEAN) | Dispersion |
|---|---|---|---|---|
| Gamma (40Hz) Stimulation | Performance in Phonematic Fluency-Rule Breaks | Baseline | 0.9 number of rule breaks | Standard Deviation 1.1 |
| Gamma (40Hz) Stimulation | Performance in Phonematic Fluency-Rule Breaks | Follow-Up (Day 2) | 2.0 number of rule breaks | Standard Deviation 2 |
| Active Control (21 Hz) Stimulation | Performance in Phonematic Fluency-Rule Breaks | Baseline | 0.7 number of rule breaks | Standard Deviation 1.3 |
| Active Control (21 Hz) Stimulation | Performance in Phonematic Fluency-Rule Breaks | Follow-Up (Day 2) | 1.0 number of rule breaks | Standard Deviation 1.3 |
Other Pre-specified
Exploration of a Relationship (Correlation) Between the Amount of Sleep Spindles and Slow Wave Sleep With Recall
A relationship is defined as a correlation (Pearson's) between memory recall performance (amount of words recalled) and sleep EEG features (especially spindles, slow waves), i.e., whether better memory recall is associated with more sleep spindles and more slow wave sleep in the night after stimulation.
Time frame: Baseline (Day 1), Follow-Up (Day 2)
Other Pre-specified
Exploration of a Relationship (Correlation) of Sleep-Wake-Schedule Changes and Type of Stimulation
To see whether there is a correlation (Pearson's) between type of stimulation/wearing EEG and the motor activity pattern (measured by actigraphy wristband).
Time frame: Baseline (Day 1), Follow-Up (Day 2)