Participants will receive sham HD-tDCS

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.

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.

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.

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.

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.

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.

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.

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.

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.

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".

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".

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".

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".

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".

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".

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".

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".

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".

Total of all reporting groups

The Mini Mental-State Examination is a 30-item global cognitive screen. Scores range from 0-30 with higher scores represent better performances and scores 23 and below are suggestive of cognitive impairment.

Participants were not screened if an MMSE was completed within the past six months as part of their involvement with the Michigan Alzheimer's Disease Center (n = 2)

Missing data for two participants

The first impedance reading averaged across all five electrodes. The unit measured is in "Quality Units" as produced by the Soterix transcranial direct current stimulation machine, which is a proprietary measurement of impedance. Lower values represent less impedance.

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.

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.

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.

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 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.

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 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.

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 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.

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 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.

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 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.

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

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.

Missing data for one participant

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.

Missing data for one participant

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.

Missing data for one participant

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.

Missing data for one participant

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.

Missing data for one participant

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.

Missing data for one participant

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.

Missing data for one participant

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.

missing data for two participants

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.

missing data for two participants

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.

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

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.

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

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.

missing data for two participants

Participants were asked to estimate which group they were in (i.e., active or sham).

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".

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".

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".

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".

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".

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".

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".

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".

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".

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".

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

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).