Patient Centered-Rehabilitation ver111090.1

Effects of 3mA HD-tDCS on Associative and Working Memory in Cognitively Intact Older Adults

Status

Completed

Phases

Study type

Interventional

Source

ClinicalTrials.gov

Registry ID

NCT03034954

Acronym

PCN1

Enrollment

Registered

2017-01-27

Start date

2016-10-31

Completion date

2017-10-31

Last updated

2018-08-16

For informational purposes only — not medical advice. Sourced from public registries and may not reflect the latest updates. Terms

Conditions

Cognitive Change

Brief summary

As we age, a number of factors can reduce our cognitive (or thinking) abilities. This study will evaluate whether transcranial electrical stimulation (TES), which uses small amounts of electricity to modulate brain functioning, can improve cognitive abilities. Here, the effects of TES on working memory, learning, and memory, will be evaluated in a group of healthy older adults.

Detailed description

The primary objective is to investigate the cognitive effects of high definition anodal tDCS (HD-tDCS; anode at center electrode) at 3 mA (for 20 minutes) on learning, memory, and working memory. Participants will be randomized to active or sham stimulation and will complete a series of cognitive tests both during and after stimulation. Tolerability and blinding will also be evaluated using standard side effect questionnaires.

Interventions

DEVICEActive HD-tDCS

Participants will receive active HD-tDCS at 3mA for 20 minutes

DEVICESham HD-tDCS

Participants will receive sham HD-tDCS

Study design

Allocation

RANDOMIZED

Intervention model

PARALLEL

Primary purpose

TREATMENT

Masking

DOUBLE (Subject, Investigator)

Eligibility

Sex/Gender

ALL

Age

50 Years to No maximum

Healthy volunteers

Yes

Inclusion criteria

1. Individuals with intact cognitive functioning. 2. Participants will be age 50 or older.

Exclusion criteria

1. Individuals with a documented history of cognitive impairment. 2. A history of serious mental illness (e.g., bipolar disorder, schizophrenia, axis 2 disorders) 3. Sensory or motor impairments that limit the ability to take part in the study 4. A significant history or current use of alcohol or drug abuse/dependence 5. Those who are currently pregnant (if there is a question of pregnancy, pregnancy tests will be available for participants at no charge) 6. Participants with an Mini Mental State Examination score \<24 at screening.

Design outcomes

Primary

Measure	Time frame	Description
Calculated Working Memory Performance Accounting for Simple Attention (Semantic 2-back d' Minus 0-back d')	30 minutes post-stimulation	The n-back is a well validated measure of working memory. During 0-back, participants are asked to respond by pressing a key when the picture on the screen is the same as the given target (e.g., a cow). During Semantic 2-back, participants are asked to respond when a picture shown is in the same semantic category as the picture two items ago (e.g., both fruits). Discriminability (d') is a measure of signal detection that accounts for signal to noise ratio. By subtracting the 0-back d', the calculated score represents a more pure working memory measure. Scores closer to zero or positive represent better working memory performance.
Object Location Touchscreen Task (Version C) Free Recall Average Error	15 minutes after encoding	The Object Location Touchscreen Task (OLTT) is a measure of object location association memory. The OLTT requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Free Recall, participants are given a blank screen and asked to touch the area of the screen an object was located. Average Score is the average error across all 15 trials. Lower scores represent better performance.
Object Location Touchscreen Task (Version C) Free Recall Average Time to Respond	15 minutes after encoding	The Object Location Touchscreen Task (OLTT) is a measure of object location association memory. The OLTT requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Free Recall, participants are given a blank screen and asked to touch the area of the screen an object was located. Average Time is the average latency to respond across all 15 trials. Lower scores represent faster responses.
Object Location Touchscreen Task (Version C) Cued Recall Total Error	15 minutes after encoding	The Object Location Touchscreen Task (OLTT) requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Cued Recall, participants are shown the room or environment on the screen and asked to touch the area of the screen an object was located. Total Score is the sum of error for all 15 trials. Lower scores represent better performance.
Object Location Touchscreen Task (Version C) Cued Recall Average Error	15 minutes after encoding	The Object Location Touchscreen Task (OLTT) requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Cued Recall, participants are shown the room or environment on the screen and asked to touch the area of the screen an object was located. Average Score is the average error across all 15 trials. Lower scores represent better performance.
Object Location Touchscreen Task (Version C) Cued Recall Average Time to Respond	15 minutes after encoding	The Object Location Touchscreen Task (OLTT) requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Cued Recall, participants are shown the room or environment on the screen and asked to touch the area of the screen an object was located. Average Time is the average latency to respond across all 15 trials. Lower scores represent faster responses.
Object Location Touchscreen Task (Version C) Recognition Total Correct	15 minutes after encoding	The Object Location Touchscreen Task (OLTT) requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Recognition, participants are asked to select the correct location of an object from three options on the screen. Recognition total is the number of correct selections on all 15 trials. Higher scores represent better performance.
Object Location Touchscreen Task (Version C) Recognition Average Time to Respond	15 minutes after encoding	The Object Location Touchscreen Task (OLTT) requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Recognition, participants are asked to select the correct location of an object from three options on the screen. Recognition Average Response Time is the average latency to respond across all 15 trials. Lower scores represent faster responses.
Performance (d') on a Simple Attention (0-back) Test	30 minutes post-stimulation	The n-back is a well validated measure of working memory. During 0-back, participants are asked to respond by pressing a key when the picture on the screen is the same as the given target (e.g., a cow). Discriminability (d') is a measure of signal detection that accounts for signal to noise ratio. Higher scores represent better discriminability.
Performance (d') on a Working Memory (2-back) Test	30 minutes post-stimulation	The n-back is a well validated measure of working memory. During 2-back, participants are asked to respond when a picture shown is the exact same as two items ago. Discriminability (d') is a measure of signal detection that accounts for signal to noise ratio. Higher scores represent better discriminability.
Performance (d') on a Working Memory (Semantic 2-back) Test	30 minutes post-stimulation	The n-back is a well validated measure of working memory. During Semantic-back, participants are asked to respond when a picture shown is in the same semantic category as the picture two items ago (e.g., both fruits). Discriminability (d') is a measure of signal detection that accounts for signal to noise ratio. Higher scores represent better discriminability.
Calculated Working Memory Performance Accounting for Simple Attention (2-back d' Minus 0-back d')	30 minutes post-stimulation	The n-back is a well validated measure of working memory. During 0-back, participants are asked to respond by pressing a key when the picture on the screen is the same as the given target (e.g., a cow). During 2-back, participants are asked to respond when a picture shown is the exact same as two items ago. Discriminability (d') is a measure of signal detection that accounts for signal to noise ratio. By subtracting the 0-back d', the calculated score represents a more pure working memory measure. Scores closer to zero or positive represent better working memory performance.
Object Location Touchscreen Task (Version C) Free Recall Total Error	15 minutes after encoding	The Object Location Touchscreen Task (OLTT) is an ecologically relevant measure of object location association memory. The OLTT requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Free Recall, participants are given a black screen and asked to touch the area of the screen an object was located. Total Score is the sum of error for all 15 trials. Lower scores represent better performance.

Secondary

Measure	Time frame	Description
Frequency of Endorsement (%) for Headache Item in Active and Sham Participants Undergoing HD-tDCS Session	~1 minute post stimulation	The side effects were assessed using a modified version of Brunoni et al. (2011) questionnaire. Participants rated common sensory experiences on a scale of None, Mild, Moderate, or Severe.
Frequency of Endorsement (%) for Neck Pain Item in Active and Sham Participants Undergoing HD-tDCS Session	~1 minute post stimulation	The side effects were assessed using a modified version of Brunoni et al. (2011) questionnaire. Participants rated common sensory experiences on a scale of None, Mild, Moderate, or Severe.
Frequency of Endorsement (%) for Scalp Pain Item in Active and Sham Participants Undergoing HD-tDCS Session	~1 minute post stimulation	The side effects were assessed using a modified version of Brunoni et al. (2011) questionnaire. Participants rated common sensory experiences on a scale of None, Mild, Moderate, or Severe.
Frequency of Endorsement (%) for Tingling Item in Active and Sham Participants Undergoing HD-tDCS Session	~1 minute post stimulation	The side effects were assessed using a modified version of Brunoni et al. (2011) questionnaire. Participants rated common sensory experiences on a scale of None, Mild, Moderate, or Severe.
Frequency of Endorsement (%) for Itching Item in Active and Sham Participants Undergoing HD-tDCS Session	~1 minute post stimulation	The side effects were assessed using a modified version of Brunoni et al. (2011) questionnaire. Participants rated common sensory experiences on a scale of None, Mild, Moderate, or Severe.
Frequency of Endorsement (%) for Burning Item in Active and Sham Participants Undergoing HD-tDCS Session	~1 minute post stimulation	The side effects were assessed using a modified version of Brunoni et al. (2011) questionnaire. Participants rated common sensory experiences on a scale of None, Mild, Moderate, or Severe.
Frequency of Endorsement (%) for Skin Redness Item in Active and Sham Participants Undergoing HD-tDCS Session	~1 minute post stimulation	The side effects were assessed using a modified version of Brunoni et al. (2011) questionnaire. Participants rated common sensory experiences on a scale of None, Mild, Moderate, or Severe.
Frequency of Endorsement (%) for Sleepiness Item in Active and Sham Participants Undergoing HD-tDCS Session	~1 minute post stimulation	The side effects were assessed using a modified version of Brunoni et al. (2011) questionnaire. Participants rated common sensory experiences on a scale of None, Mild, Moderate, or Severe.
Frequency of Endorsement (%) for Concentration Changes Item in Active and Sham Participants Undergoing HD-tDCS Session	~1 minute post stimulation	The side effects were assessed using a modified version of Brunoni et al. (2011) questionnaire. Participants rated common sensory experiences on a scale of None, Mild, Moderate, or Severe.
Frequency of Endorsement (%) for Mood Changes Item in Active and Sham Participants Undergoing HD-tDCS Session	~1 minute post stimulation	The side effects were assessed using a modified version of Brunoni et al. (2011) questionnaire. Participants rated common sensory experiences on a scale of None, Mild, Moderate, or Severe.
Blinding in Total Sample	~1 minute post stimulation	Participants were asked to estimate which group they were in (i.e., active or sham).

Countries

United States

Participant flow

Pre-assignment details

Two participants were excluded after consent due to failing the tDCS safety screen. One participant endorsed a skin condition with lesions at site of electrode placement. One participant disclosed a prior head injury.

Participants by arm

Arm	Count
Active HD-tDCS Participants will receive real HD-tDCS (3 milliamps for 20 minutes) for a single session. Active HD-tDCS: Participants will receive active HD-tDCS at 3mA for 20 minutes	19
Sham HD-tDCS Participants will undergo the exact same procedures as the active group but will receive sham stimulation for a single session. Sham HD-tDCS: Participants will receive sham HD-tDCS	21
Total	40

Withdrawals & dropouts

Period	Reason	FG000	FG001
Overall Study	Machine malfunction; did not reach 3 mA	1	0

Baseline characteristics

Characteristic	Active HD-tDCS	Sham HD-tDCS	Total
Age, Continuous	66.42 years STANDARD_DEVIATION 8.546	65.38 years STANDARD_DEVIATION 10.604	65.88 years STANDARD_DEVIATION 9.573
Education	16.82 years STANDARD_DEVIATION 1.59	16.48 years STANDARD_DEVIATION 2.089	16.63 years STANDARD_DEVIATION 1.866
Ethnicity (NIH/OMB) Hispanic or Latino	0 Participants	0 Participants	0 Participants
Ethnicity (NIH/OMB) Not Hispanic or Latino	19 Participants	21 Participants	40 Participants
Ethnicity (NIH/OMB) Unknown or Not Reported	0 Participants	0 Participants	0 Participants
Impedance	0.9512 quality units STANDARD_DEVIATION 0.4004	0.8939 quality units STANDARD_DEVIATION 0.06314	0.921 quality units STANDARD_DEVIATION 0.528
Mini-Mental State Examination	28.58 units on a scale STANDARD_DEVIATION 1.216	28.37 units on a scale STANDARD_DEVIATION 1.212	28.47 units on a scale STANDARD_DEVIATION 1.202
Object Location Touchscreen Task (Version B) Cued Recall Average Error	4.971 centimeters STANDARD_DEVIATION 3.422	3.002 centimeters STANDARD_DEVIATION 2.574	3.937 centimeters STANDARD_DEVIATION 3.129
Object Location Touchscreen Task (Version B) Cued Recall Average Time to Respond	3855.83 milliseconds STANDARD_DEVIATION 2452.1	3307.879 milliseconds STANDARD_DEVIATION 1605.689	3568.155 milliseconds STANDARD_DEVIATION 2043.063
Object Location Touchscreen Task (Version B) Cued Recall Total Error	74.513 centimeters STANDARD_DEVIATION 51.385	45.055 centimeters STANDARD_DEVIATION 38.61	59.048 centimeters STANDARD_DEVIATION 46.958
Object Location Touchscreen Task (Version B) Free Recall Average Error	7.685 centimeters STANDARD_DEVIATION 2.963	6.835 centimeters STANDARD_DEVIATION 2.97	7.239 centimeters STANDARD_DEVIATION 2.96
Object Location Touchscreen Task (Version B) Free Recall Average Time to Respond	3796.361 milliseconds STANDARD_DEVIATION 1188.015	4921.558 milliseconds STANDARD_DEVIATION 2306.631	4387.09 milliseconds STANDARD_DEVIATION 1924.503
Object Location Touchscreen Task (Version B) Free Recall Total Error	115.27 centimeters STANDARD_DEVIATION 44.445	102.534 centimeters STANDARD_DEVIATION 6.835	108.583 centimeters STANDARD_DEVIATION 7.239
Object Location Touchscreen Task (Version B) Recognition Average Time to Respond	3005.095 milliseconds STANDARD_DEVIATION 1807.47	2456.063 milliseconds STANDARD_DEVIATION 1164.46	2716.853 milliseconds STANDARD_DEVIATION 1510.062
Object Location Touchscreen Task (Version B) Recognition Total Correct	13.11 number of correct answers STANDARD_DEVIATION 1.941	14.05 number of correct answers STANDARD_DEVIATION 1.322	13.6 number of correct answers STANDARD_DEVIATION 1.692
Race (NIH/OMB) American Indian or Alaska Native	0 Participants	0 Participants	0 Participants
Race (NIH/OMB) Asian	0 Participants	1 Participants	1 Participants
Race (NIH/OMB) Black or African American	0 Participants	1 Participants	1 Participants
Race (NIH/OMB) More than one race	0 Participants	0 Participants	0 Participants
Race (NIH/OMB) Native Hawaiian or Other Pacific Islander	1 Participants	0 Participants	1 Participants
Race (NIH/OMB) Unknown or Not Reported	0 Participants	0 Participants	0 Participants
Race (NIH/OMB) White	18 Participants	19 Participants	37 Participants
Region of Enrollment United States	19 Participants	21 Participants	40 Participants
Sex: Female, Male Female	11 Participants	16 Participants	27 Participants
Sex: Female, Male Male	8 Participants	5 Participants	13 Participants

Adverse events

Event type	EG000 affected / at risk	EG001 affected / at risk
deaths Total, all-cause mortality	0 / 19	0 / 21
other Total, other adverse events	16 / 19	19 / 21
serious Total, serious adverse events	0 / 19	0 / 21

Outcome results

Primary

Calculated Working Memory Performance Accounting for Simple Attention (2-back d' Minus 0-back d')

The n-back is a well validated measure of working memory. During 0-back, participants are asked to respond by pressing a key when the picture on the screen is the same as the given target (e.g., a cow). During 2-back, participants are asked to respond when a picture shown is the exact same as two items ago. Discriminability (d') is a measure of signal detection that accounts for signal to noise ratio. By subtracting the 0-back d', the calculated score represents a more pure working memory measure. Scores closer to zero or positive represent better working memory performance.

Time frame: 30 minutes post-stimulation

Population: missing data for 12 participants: 11 2-back (5 Active; 6 sham) due to Eprime miscalculation \& one 0-back (Active)

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Calculated Working Memory Performance Accounting for Simple Attention (2-back d' Minus 0-back d')	-1.130 d'	Standard Deviation 0.629
Sham HD-tDCS	Calculated Working Memory Performance Accounting for Simple Attention (2-back d' Minus 0-back d')	-1.31 d'	Standard Deviation 0.675

Primary

Calculated Working Memory Performance Accounting for Simple Attention (Semantic 2-back d' Minus 0-back d')

The n-back is a well validated measure of working memory. During 0-back, participants are asked to respond by pressing a key when the picture on the screen is the same as the given target (e.g., a cow). During Semantic 2-back, participants are asked to respond when a picture shown is in the same semantic category as the picture two items ago (e.g., both fruits). Discriminability (d') is a measure of signal detection that accounts for signal to noise ratio. By subtracting the 0-back d', the calculated score represents a more pure working memory measure. Scores closer to zero or positive represent better working memory performance.

Time frame: 30 minutes post-stimulation

Population: missing data for two participants

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Calculated Working Memory Performance Accounting for Simple Attention (Semantic 2-back d' Minus 0-back d')	-2.69 d'	Standard Deviation 0.58
Sham HD-tDCS	Calculated Working Memory Performance Accounting for Simple Attention (Semantic 2-back d' Minus 0-back d')	-2.56 d'	Standard Deviation 0.47

Comparison: A Multivariate ANOVA was used to compare Active vs. Sham groups on discriminability measures (i.e. 0-back d', 2-back d', semantic 2-back d') and calculated working memory measures (i.e., 2-back d' minus 0-back d', semantic 2-back d' minus 0-back d').p-value: 0.45MANOVA

Primary

Object Location Touchscreen Task (Version C) Cued Recall Average Error

The Object Location Touchscreen Task (OLTT) requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Cued Recall, participants are shown the room or environment on the screen and asked to touch the area of the screen an object was located. Average Score is the average error across all 15 trials. Lower scores represent better performance.

Time frame: 15 minutes after encoding

Population: Missing data for one participant

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Object Location Touchscreen Task (Version C) Cued Recall Average Error	4.453 centimeters	Standard Deviation 1.954
Sham HD-tDCS	Object Location Touchscreen Task (Version C) Cued Recall Average Error	2.919 centimeters	Standard Deviation 1.954

Primary

Object Location Touchscreen Task (Version C) Cued Recall Average Time to Respond

The Object Location Touchscreen Task (OLTT) requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Cued Recall, participants are shown the room or environment on the screen and asked to touch the area of the screen an object was located. Average Time is the average latency to respond across all 15 trials. Lower scores represent faster responses.

Time frame: 15 minutes after encoding

Population: Missing data for one participant

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Object Location Touchscreen Task (Version C) Cued Recall Average Time to Respond	3991.659 milliseconds	Standard Deviation 2218.596
Sham HD-tDCS	Object Location Touchscreen Task (Version C) Cued Recall Average Time to Respond	2666.858 milliseconds	Standard Deviation 866.887

Comparison: Univariate analysis of the OLTT Cued Recall Average Time to Respond following significant multivariate repeated measures ANOVA comparing baseline OLTT (Version B) to post-tDCS OLTT (Version C) across the treatment groups (Active vs. Sham).p-value: 0.15Repeated Measures ANOVA

Primary

Object Location Touchscreen Task (Version C) Cued Recall Total Error

The Object Location Touchscreen Task (OLTT) requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Cued Recall, participants are shown the room or environment on the screen and asked to touch the area of the screen an object was located. Total Score is the sum of error for all 15 trials. Lower scores represent better performance.

Time frame: 15 minutes after encoding

Population: Missing data for one participant

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Object Location Touchscreen Task (Version C) Cued Recall Total Error	66.806 centimeters	Standard Deviation 29.303
Sham HD-tDCS	Object Location Touchscreen Task (Version C) Cued Recall Total Error	43.775 centimeters	Standard Deviation 29.32

Primary

Object Location Touchscreen Task (Version C) Free Recall Average Error

The Object Location Touchscreen Task (OLTT) is a measure of object location association memory. The OLTT requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Free Recall, participants are given a blank screen and asked to touch the area of the screen an object was located. Average Score is the average error across all 15 trials. Lower scores represent better performance.

Time frame: 15 minutes after encoding

Population: Missing data for one participant

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Object Location Touchscreen Task (Version C) Free Recall Average Error	8.099 centimeters	Standard Deviation 1.757
Sham HD-tDCS	Object Location Touchscreen Task (Version C) Free Recall Average Error	6.652 centimeters	Standard Deviation 1.856

Primary

Object Location Touchscreen Task (Version C) Free Recall Average Time to Respond

The Object Location Touchscreen Task (OLTT) is a measure of object location association memory. The OLTT requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Free Recall, participants are given a blank screen and asked to touch the area of the screen an object was located. Average Time is the average latency to respond across all 15 trials. Lower scores represent faster responses.

Time frame: 15 minutes after encoding

Population: Missing data for one participant

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Object Location Touchscreen Task (Version C) Free Recall Average Time to Respond	3419.878 milliseconds	Standard Deviation 1690.354
Sham HD-tDCS	Object Location Touchscreen Task (Version C) Free Recall Average Time to Respond	3029.648 milliseconds	Standard Deviation 1572.416

Comparison: A Repeated Measures ANOVA was used to compare baseline OLTT (Version B) to post-tDCS OLTT (Version C) across the treatment groups (Active vs. Sham). The multivariate analyses included OLTT Response Times (i.e., Free Recall Average Response Time, Cued Recall Average Response Time, Recognition Average Response Time)p-value: 0.044Repeated Measures ANOVA

Comparison: Univariate analysis of the OLTT Free Recall Average Time to Respond following significant multivariate repeated measures ANOVA comparing baseline OLTT (Version B) to post-tDCS OLTT (Version C) across the treatment groups (Active vs. Sham).p-value: 0.006Repeated Measures ANOVA

Primary

Object Location Touchscreen Task (Version C) Free Recall Total Error

The Object Location Touchscreen Task (OLTT) is an ecologically relevant measure of object location association memory. The OLTT requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Free Recall, participants are given a black screen and asked to touch the area of the screen an object was located. Total Score is the sum of error for all 15 trials. Lower scores represent better performance.

Time frame: 15 minutes after encoding

Population: Missing data for one participant

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Object Location Touchscreen Task (Version C) Free Recall Total Error	121.498 centimeters	Standard Deviation 26.366
Sham HD-tDCS	Object Location Touchscreen Task (Version C) Free Recall Total Error	99.77 centimeters	Standard Deviation 27.845

Comparison: We used a multivariate statistic to compare OLTT means (Free Recall Total Error, Free Recall Average Error, Cued Recall Total Error, Cued Recall Average Error, Recognition Total Correct) at baseline (Version B) to post HD-tDCS OLTT means (Version C), by groups (active vs. sham). The overall statistic represents the simultaneous comparison of baseline OLTT measures to post HD-tDCS OLTT measures.p-value: 0.3Repeated Measures ANOVA

Primary

Object Location Touchscreen Task (Version C) Recognition Average Time to Respond

The Object Location Touchscreen Task (OLTT) requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Recognition, participants are asked to select the correct location of an object from three options on the screen. Recognition Average Response Time is the average latency to respond across all 15 trials. Lower scores represent faster responses.

Time frame: 15 minutes after encoding

Population: Missing data for one participant

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Object Location Touchscreen Task (Version C) Recognition Average Time to Respond	2804.459 milliseconds	Standard Deviation 1244.249
Sham HD-tDCS	Object Location Touchscreen Task (Version C) Recognition Average Time to Respond	1903.39 milliseconds	Standard Deviation 843.244

Comparison: Univariate analysis of the OLTT Recognition Average Time to Respond following significant multivariate repeated measures ANOVA comparing baseline OLTT (Version B) to post-tDCS OLTT (Version C) across the treatment groups (Active vs. Sham).p-value: 0.3Repeated Measures ANOVA

Primary

Object Location Touchscreen Task (Version C) Recognition Total Correct

The Object Location Touchscreen Task (OLTT) requires participants to learn and recall the location of 15 object-location associations. Memory is evaluated using a touchscreen monitor, which allows for the continuous measurement of memory accuracy (i.e., distance from targeted location). During the Recognition, participants are asked to select the correct location of an object from three options on the screen. Recognition total is the number of correct selections on all 15 trials. Higher scores represent better performance.

Time frame: 15 minutes after encoding

Population: Missing data for one participant

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Object Location Touchscreen Task (Version C) Recognition Total Correct	12.79 number of correct answers	Standard Deviation 1.932
Sham HD-tDCS	Object Location Touchscreen Task (Version C) Recognition Total Correct	13.45 number of correct answers	Standard Deviation 1.669

Primary

Performance (d') on a Simple Attention (0-back) Test

The n-back is a well validated measure of working memory. During 0-back, participants are asked to respond by pressing a key when the picture on the screen is the same as the given target (e.g., a cow). Discriminability (d') is a measure of signal detection that accounts for signal to noise ratio. Higher scores represent better discriminability.

Time frame: 30 minutes post-stimulation

Population: missing data for two participants

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Performance (d') on a Simple Attention (0-back) Test	4.26 d'	Standard Deviation 0.231
Sham HD-tDCS	Performance (d') on a Simple Attention (0-back) Test	4.25 d'	Standard Deviation 0.219

Primary

Performance (d') on a Working Memory (2-back) Test

The n-back is a well validated measure of working memory. During 2-back, participants are asked to respond when a picture shown is the exact same as two items ago. Discriminability (d') is a measure of signal detection that accounts for signal to noise ratio. Higher scores represent better discriminability.

Time frame: 30 minutes post-stimulation

Population: missing data for two participants

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Performance (d') on a Working Memory (2-back) Test	3.05 d'	Standard Deviation 0.508
Sham HD-tDCS	Performance (d') on a Working Memory (2-back) Test	2.94 d'	Standard Deviation 0.675

Primary

Performance (d') on a Working Memory (Semantic 2-back) Test

The n-back is a well validated measure of working memory. During Semantic-back, participants are asked to respond when a picture shown is in the same semantic category as the picture two items ago (e.g., both fruits). Discriminability (d') is a measure of signal detection that accounts for signal to noise ratio. Higher scores represent better discriminability.

Time frame: 30 minutes post-stimulation

Population: missing data for eleven participants (5 Active; 6 Sham) due to Eprime miscalculation

Arm	Measure	Value (MEAN)	Dispersion
Active HD-tDCS	Performance (d') on a Working Memory (Semantic 2-back) Test	1.518 d'	Standard Deviation 0.537
Sham HD-tDCS	Performance (d') on a Working Memory (Semantic 2-back) Test	1.69 d'	Standard Deviation 0.495

Secondary