Feasibility of Gamma Transcranial Alternating Current Stimulation to Reduce Beta-amyloid Load and Improve Memory
Phase: NA
Conditions: Mild Cognitive Impairment
Sponsor: University of California, San Francisco

Study Protocol & Statistical Analysis Plan 
 
Title: Feasibility of Gamma Transcranial Alternating Current Stimulation to 
Reduce Beta-amyloid Load and Improve Memory 
 
NCT#: NCT04646499 
 
Last Updated: 11/02/2021 
 
 

Participants.  
This study was preregistered at ClinicalTrials.gov with identifier NCT04646499. The 
study protocol was approved by the University of California San Francisco (UCSF) 
Institutional Review Board and all participants signed informed consent documents prior 
to participating in the study. Participants received $20 per hour for participation and a 
$50 bonus for completion of the study. To be eligible for this study, all participants were 
60-80 years of age, fluent in English, had at least 12 years of education, and had normal 
or corrected-to-normal vision. In addition, participants had to have aMCI (see below for 
aMCI inclusion criteria) and be able to complete cognitive tasks and cooperate with all 
study procedures. The exclusion criteria were as follows: neurological or psychiatric 
disorders other than aMCI, receiving investigational medications or participated in a 
clinical trial with medications within the previous 30 days, family history of epilepsy, 
implanted electronic devices (e.g. pacemaker), prior serious head trauma, pregnant, or 
IQ under 80. In addition, participants were not on cholinesterase inhibitors, memantine, 
psychotropics, anti-depressants, or anti-anxiety medications. Finally, participants did not 
have color vision deficiency, a history of substance abuse, glaucoma, macular 
degeneration, amblyopia, or strabismus. 
Fourteen older adults with aMCI were enrolled and 13 completed the entire 
intervention in a single-arm design (age mean: 73.62 years (SD: 5.44), Montreal 
Cognitive Assessment mean (MoCA): 23.39 (SD: 3.66), Education years mean: 17.69 
(SD: 2.78), 7 Male, 11 right-handed). Prior to enrolling in the study, all participants 
completed the Montreal Cognitive Assessment (MoCA). In the current study, participants 
were considered aMCI by scoring between 27 and 16 on the MoCA and had a self-
complaint of memory difficulty. In addition, participants needed an age-matched Z-score 
of at least -1 on immediate memory or delayed memory (as measured by the California 
Verbal Learning Test, short version) and at least -1 Z-score on verbal fluency (D words), 
semantic fluency (animals), processing speed (digit symbol and number trails tasks), or 
task switching (number letter trails task). All participants also scored as having intact 
activities of daily living by scoring as mostly independent on the IADL. Finally, all 
participants had the presence of both AB and tau in the pre-tACS phlebotomy biomarker 
analyses, indicating that MCI status is likely due to progression towards AD as opposed 
to other potential causes of cognitive decline. One participant withdrew voluntarily prior 
to any cognitive assessment or tACS. 
 
Study Timeline.  
The study required 10 visits to UCSF over 5 weeks. During visit 1, participants 
completed baseline assessments of the instrumental activities of daily living (IADL) 
survey, cognitive tests assessing baseline episodic memory performance, and an MRI 
scan (Week 1). On the following week, participants received gamma tACS while 
engaged in the Stimulation Tasks (see details below) on five consecutive weekdays 
(Week 2, visits 2-6, Monday-Friday). On one day during each of the three following 
weeks, participants also completed the Stimulation Tasks while receiving gamma tACS 
(Weeks 3-5, visits 7-9). These sessions occurred on the same day of the week for each 
participant (e.g. consecutive Tuesdays), with a small number occurring ± one day. 
Finally, during the 5th week (visit 10), participants completed the same procedure as the 
baseline assessment (visit 1), which included the IADL survey, tests of episodic memory, 
and an MRI scan. All study activities took place at UCSF, except for one participant who 
completed the eight tACS sessions in their home. For this participant, a researcher was 
present with the required tACS equipment during the at-home sessions, and the 
participant completed the MRI and outcome assessments at UCSF.  

 
Surveys.  
Participants completed the Instrumental Activities of Daily Living (IADL) during the initial 
pre-tACS and post-tACS follow-up Cognitive Task sessions (Weeks 1 and 5, 
respectively) . Additionally, following each tACS session, participants filled out a 
tolerability survey of the following 11 measures on a scale of 0 (not noticeable) to 10 (not 
tolerable): headache, neck pain, scalp pain, tingling, itching, burning sensation, 
increased alertness, increased sleepiness, trouble concentrating, acute mood change, 
and presence of phosphenes. Prior to the initial tACS session (Week 1) participants 
completed surveys that measure their anticipation, anxiety, and expected benefits on 
both memory and cognition following tACS on a scale of 1 - 10. Following the final tACS 
session (Week 5), participants were probed on the same categories for their perceived 
benefits of the tACS intervention. 
 
Magnetic Resonance Imaging.  
Participants completed two MRI sessions with the same protocol prior to and following 
the tACS intervention (i.e., during the pre- and post-tACS phases, respectively). All data 
was collected by a Siemens 3T MAGNETOM Trio MRI using a 64-channel head coil. 
First, high-resolution T1-weighted anatomical images were acquired (1 x 1 x 1 mm voxel 
size, FOV = 160 x 240 x 256 mm, repetition time (TR) = 2300 ms, echo time (TE) = 3 
ms, flip angle (FA) = 9°). For MRS, two voxels were placed in the left Pars, and left Hipp 
(3x3x2 cm each) based on the T1 structural scan. We then collected GABA-edited 
MEGA-PRESS scans (TR/TE = 2000/68 ms, 128 averages, FA = 90°), with editing 
pulses at 1.9 edit-ON and 7.2 edit-OFF ppm. The edit-ON and edit-OFF differences yield 
the peaks affected by the editing pulses.  
Next, participants completed approximately six-minutes of eyes-closed resting-
state functional MRI (rs-fMRI) using a T2*-weighted echoplanar imaging (EPI) sequence 
with the following parameters: 560 volumes, TR = 850 ms, TE = 32.8 ms, FA = 45°, in-
plane resolution = 2.2 mm2, 66 total 2.2 mm slices using a multiband acceleration factor 
of 6. Participants were instructed to close their eyes, remain awake, and be as still as 
possible. Last, DTI data was collected with 10 non-diffusion weighted images (b = 0 
s/mm2) followed by 96 diffusion weighted images (b = 2500 s/mm2; TR = 2420 ms, TE= 
72.2 ms, and FA = 85°). One participant did not have usable rs-fMRI at their post-tACS 
session due to imaging artifacts, resulting in usable datasets from 12 participants for 
these analyses. One participant did not have baseline DTI data due to time constraints in 
the MRI, resulting in usable datasets from 12 participants for these analyses. 
 
Phlebotomy. 
Participants had two phlebotomy sessions immediately after their pre- and post- MRI 
sessions, on days with baseline behavioral assessments in Week 1 and the final tACS 
session in Week 5, respectively. Before both sessions, participants were instructed to 
fast from any food intake prior to arrival for a minimum of 4 hours. Following the session, 
participants had an opportunity to rest and eat food. On both sessions, participants 
underwent a draw of 20 mL of blood in two 10 mL vials. These vials were immediately 
delivered to the sample processing lab located on the floor above the phlebotomy lab 
where the samples were centrifuged at 200 x g for 15 min at 4 °C then put in storage 
until analysis. At the end of data collection, the entire sample was gradually brought to 
room temperature for analysis. All analyses were conducted by a board-certified 
laboratory technician blinded to the hypotheses of our study. This pre- and post-tACS 
analyses of the blood draw samples allow for changes in measures of amyloid, tau, and 
NfL.  

 
Neuromodulation.  
Participants were fitted with a neoprene head cap with electrodes located at 8 locations 
bilaterally (F7, F8, FT7, FT8, T7, T8, P7, and P8; 10-20 EEG system). The tACS was 
delivered through an 8-channel mobile Starstim device (Neuroelectrics, Spain) with NG 
Pistim electrodes (contact area: 3.14 cm2). On each session the tACS current was 
ramped up slowly over 4 minutes to a total of 1.6 mA (0.4 mA per electrode baseline to 
peak, with the four contralateral electrodes set to 180° offset), maintained full strength 
for 52 minutes, then ramp back down to 0 mA over 4 min. We sought to target multiple 
regions of the cortex known to be related to MCI, AD, and episodic memory processing: 
the Hipp, IPL, and Pars. Based on our preliminary research in mouse models of AD, 
which tested whether there was a dose-response curve with greater stimulation 
strengths and durations1, we observed that the greatest doses of gamma oscillatory 
current had the strongest effects. Therefore, we applied the highest dose of stimulation 
that we believed would be tolerable to adults with MCI, without inducing overly 
distracting side effects such as phosphenes or physical sensations that are more likely 
at higher stimulation doses. During each of the eight 60-minute tACS sessions, 
participants engaged in the Stimulation Tasks (see below for details). Following the end 
of each tACS session, participants filled out a survey of side effects (see Surveys 
above). 
 
Cognitive Testing.  
During Week 1, prior to any tACS sessions, participants first completed the California 
Verbal Learning Test (CVLT) to assess aspects of episodic memory, including delayed 
free-recall, and cued recall/recognition. The CVLT is a task known to positively correlate 
with hippocampal size, act as an early detector of AD, and track disease progression 
such as demyelination in multiple sclerosis. Participants completed the standard and 
alternate versions of the CVLT during the initial cognitive testing session (Week 1) and 
the final Cognitive Testing session (Week 5), with the order counterbalanced across 
participants. The CVLT has a 20-minute and a 10-minute break period, with the former 
separating the short-delay free recall (SDFR) from the long-delay free recall (LDFR), and 
the latter break separating the LDFR from the force-choice recognition portion.  
During the CVLT 20-minute break, participants completed the Paired Associates 
Task (PAT). The PAT assesses episodic memory via recall and recognition of pairs of 
face and scene stimuli and, therefore, was selected so that the stimuli would not 
interfere with the verbal words encoded during the CVLT. We used a modified version of 
the PAT, where the stimulus presentation timing was increased by 500 ms to 2500 ms; 
however, the trial count and task demands were the same as the PAT in Voskontas et 
al.2. The task begins with an encoding period consisting of 10 face-scene pairs. After the 
presentation of each face-scene pair (2500 ms), participants judged whether the person 
is in an indoor (‘D’ key) or outdoor scene (‘K’ key). The 10 face-scene pairs were 
presented randomly six times each. Immediately following the PAT encoding period, 
participants were tested in the recall period where they were presented with one face or 
scene (2500 ms) followed by three items of the other category (scenes or faces, 
respectively). Participants then responded (untimed) with which of the three items they 
believed was paired with the initial stimulus presented during the encoding phase. Each 
face and scene item pair were used as the probe three times resulting in 60 total recall 
trials. Following the end of the PAT recall period, participants were presented with a 
recognition task where they were shown either correctly matched or incorrectly matched 
face-scene pairs (untimed). Correct face-scene pairs were presented three times in 
random order each and incorrect pairs were presented 60 times resulting in 90 trials. An 

alternate version of the PAT task was used during the final cognitive testing session with 
unique stimuli (Week 5) and these two versions were counterbalanced between 
participants.  
During the CVLT 10-minute break, participants completed a verbal and semantic 
fluency task where they had 60 seconds to say as many words as possible that begin 
with the given letter or fit the category (excluding proper nouns). During the pre- and 
post-tACS intervention (visits 1 and 10) participants completed the categories F, A, S, 
and animals. The cognitive testing always occurred at the beginning of the day, so that 
no fatigue effects lowered participant performance and to ensure that participants could 
successfully complete both standardized memory tests (CVLT) as well as the 
computerized memory test (PAT). 
 
Stimulation Tasks. 
Once the tACS began, participants completed a series of Stimulation Tasks designed to 
engage episodic memory. First, they completed the Mnemonic Discrimination Task 
(MDT3), which assesses high-fidelity long-term memory (LTM). During each tACS 
session, participants completed the MDT with unique stimuli consisting of common real-
world items. This resulted in eight versions of the MDT, which were counterbalanced in 
order between participants (forwards or backwards order). Immediately after the tACS 
began, participants completed the encoding portion of the MDT task. During encoding, 
participants were cued first with “will the object fit inside a lady’s shoe box?” Following 
the prompt, participants viewed 39 items in a random order and responded to the 
question for each item with an untimed button press. Next, participants were presented 
with a second cue “can you carry the object across the room using only one hand?” 
Participants then responded to this question following a random presentation of the 
same 39 items. All items were presented for 2500 ms followed by a screen that that 
listed the button press responses (“D” for yes, “K” for no). A fixation cross was presented 
on the screen for 1000 ms between trials. The MDT encoding portion of the task is timed 
to last 8-10 minutes. All versions of the MDT task were created using PsychoPy. 
 
Following the MDT encoding period, participants completed 20 minutes of a 
commercially available tablet game, Spot the Difference. This game was chosen so that 
participants are mentally engaged in a visual search task that has no interference with 
recently encoded items from the MDT task and not a task that would evoke stress due to 
task difficulty. Participants completed this task at their own pace and advanced to new 
images without any score being kept. Next, participants completed the semantic fluency 
task with three letters and a category similar to the cognitive testing with F, A, S, and 
animals (see above). Here, we created 8 unique sets each consisting of three letter 
prompts and one semantic category. Thus, the fluency task was not repeated across any 
of the tACS sessions and was different from the fluency tasks used as our Cognitive 
Tasks outcome measures. Participants were instructed to name as many items as 
possible.  
 
During the final 10 minutes, participants completed three MDT test blocks where 
they viewed 13 items seen during encoding, 13 items that were an alternate (similar) 
version of the encoded items, and five novel lures. For each item participants responded 
as to whether they were the same exact item from the encoding task from the beginning 
of stimulation. Each item was viewed for 2500 ms and followed by a screen where 
participants would respond whether the item was definitely old (“D” key), maybe old (“F” 
key), maybe new (“J” key), or definitely new (“K” key). A fixation cross was presented on 
the screen for 1000 ms between trials. The order of the target, lure, and novel items was 
random within each of the three testing blocks. In total, the tasks for the participant to 
complete during stimulation are equal to the length of the tACS session (1 hour). 

 
Data Processing and Statistical Analysis. 
Given the relatively small number of participants this study, we used non-parametric 
tests for all statistical analyses to reduce influence from potential extreme values. 
Changes in outcome metrics were assessed with non-parametric Wilcoxon sign-ranked 
tests. We also report rank-biserial correlations (rrb) to represent effect sizes of these 
changes, similar to Cohen’s d. We set a significance threshold of p < 0.05 and report 
non-significant ‘trends’ at p < 0.10. As this is a hypothesis-generating pilot study, we did 
not correct for multiple comparisons for each test conducted.  
 
Primary Outcomes.  
Our primary outcome measures were feasibility and tolerability of eight sessions of 
gamma tACS. To assess these, we measured dropout rate of participants and the 
reported side effects collected following each stimulation session. Analysis of the side 
effects collected following the end of tACS consist of the average across all 8 sessions 
for the 11 potential categories. These metrics were rated on a scale of 0 (not noticeable) 
to 10 (not tolerable). As this was a single-arm design, we compared side effect ratings 
from this study to those from a recently completed a multi-session tACS intervention in 
healthy older adults of the same age range, in which we administered 1 mA of 6 Hz 
tACS to the prefrontal cortex (F3-F4, 10-20 EEG system). This allows for an age-
matched comparison between prior stimulation protocols and one that is higher in dose 
(1 mA vs 1.6 mA), frequency (6 Hz and 40 Hz), and duration (~20 minutes and 60 
minutes) employed in the current study. As both studies included the same side-effects 
questionnaire categories, we conducted a non-parametric Mann-Whitney U test to 
assess differences in the average ratings for each metric between the two studies. 
 
Secondary Behavioral Outcomes.  
Secondary outcome measures assessed changes in performance on the memory and 
fluency tasks (CVLT, PAT, fluency). The CVLT is a standardized cognitive test with 
different task demands at each stage. For CVLT, we focused on the correct items 
named during the short-delay free recall (SDFR) and long-delay free recall (LDFR) 
sections. For the PAT, we measured accuracy for both the recall and recognition 
portions. For the semantic (animals) and verbal (F, A, S) fluency task, we measured the 
number of correct non-repeated words.  
 
Secondary Phlebotomy Outcomes. 
Blood was collected by phlebotomy in EDTA tubes and centrifuged at 2,000 g for 10 min 
at 4°C. Plasma was then aliquoted in 500 microliter polypropylene tubes, and stored at -
80°C until analyses, with an average needle-to-frozen storage time < 2 hours. Plasma 
was analyzed according to vendor protocols, using commercially available kits Neuro 4-
PLEX E [amyloid b1-42 (Ab42), amyloid b1-40 (Ab40), neurofilament light chain (NfL), and 
glial fibrillary acidic protein (GFAP)] and P-tau181 for single molecule arrays in an HD-X 
analyzer (Quanterix, Billerica, MA). Lowest level of quantification and average coefficient 
of variations were 0.378 pg/mL, 4.1% for Ab42; 1.02 pg/mL, 3.5% for Ab40; 0.4 pg/mL, 
4.3% for NfL; 2.89 pg/mL, 4.6% for GFAP; and 0.4 pg/mL, 10.1% for P-tau181. Analyzed 
samples underwent only one thaw cycle prior to use. Samples were run in duplicate, with 
kits from the same lot. Following analysis, we were able to measure the picograms per 
milliliter (pg/mL) of each of the three AD biomarkers at both time points, to quantify 
stimulation-related changes in AD biomarker levels between the two time points.  
 
 

Exploratory Behavioral Outcomes.  
We examined changes in MDT task performance as a non-registered exploratory 
measure, focusing on the changes in the lure discrimination index (LDI, proportion lure 
correct rejection—proportion novel false alarm) between the initial tACS session and 
final tACS session. Changes in performance were assessed with a Wilcoxon sign-rank 
test. As the MDT task was completed concurrently with the tACS, it is important to note 
that changes in MDT performance reflect gains during tACS from repeated test 
performance, rather than transfer to an untrained task, as with our secondary outcomes. 
In addition to examining changes in this study population, however, we also compared 
initial and final LDI performance in these MCI participants to a placebo training control 
group of healthy older adults from a previous study, where no training-related MDT gains 
were expected. For this analysis, we compared both initial and final performance 
between these groups using non-parametric Mann-Whitney U tests.  
Further, we examined changes in IADL from pre-tACS to post-tACS as an 
exploratory measure on each of the categories: bathing, dressing, grooming, mouth 
care, toileting, transferring bed/chair, walking, climbing stairs, eating, shopping, cooking, 
managing medications, phone use, housework, driving/transport, and managing 
finances. Specifically, we measured change in the IADL metrics from the pre-tACS to 
post-tACS session by measuring the average rating across all IADL categories and 
comparing these in non-parametric Wilcoxon signed-rank tests between the pre-tACS 
baseline and post-tACS follow-up sessions. 
 
Resting State Functional MRI.  
We conducted exploratory analyses on the rs-fMRI data collected during the pre- and 
post-tACS scans. Standard preprocessing of MRI data for functional connectivity 
analyses was carried out with AFNI and FreeSurfer. First, participants’ T1-weighted 
anatomical images were skull-stripped and segmented into gray matter, white matter, 
and cerebrospinal fluid (CSF) using FreeSurfer. Next, EPI data was pre-processed using 
afni_proc.py in AFNI. First, the de-spike option was applied to interpolate extreme outlier 
timepoints from the BOLD signal intensity time courses. Next, the EPI data was motion 
corrected (aligning each EPI volume to the volume with the minimum outlier fraction), co-
registered to the T1-weighted anatomical image, warped to MNI space, and resampled 
to an isotropic resolution of 2 mm3. Further, we implemented noise reduction by 
regressing out several ‘nuisance’ variables: (1) 12 motion regressors (6 realignment 
parameters and their derivatives), (2) voxel-wise local white matter regressors using 
AFNI’s fast ANTATICOR method, and (3) the top 3 principal components from lateral 
ventricle voxels. EPI data was also bandpass filtered (0.01-0.10 Hz) and volumes with 
excessive motion (> 1 mm root mean square motion) and the volume prior were 
censored. Nuisance regression, bandpass filtering, and censoring were performed in a 
single step. 
To measure functional connectivity, we quantified Pearson’s correlations (and 
applied a Fisher z-transform) between ROI timeseries from Pars, IPL, and Hipp (left and 
right) during the baseline and follow-up MRI sessions. Pars and Hipp ROIs were 
automatically output from the MRS scan (see below) and we generated an additional IPL 
ROI in FSL. We copied each left hemisphere mask to the right hemisphere to generate 
masks for all six regions. We calculated functional connectivity as the average 
connectivity between each ROI pair between and within hemispheres (e.g., IPL-Hipp 
connectivity calculated as the average of right IPL-Hipp, left IPL-Hipp, right IPL – left 
Hipp, and left IPL – right Hipp). We note that RSFC for one participant had relatively high 
values at baseline for each ROI pairing (average RSFC: 0.64) compared to the other 
participants, despite having no visible artifacts or excessive motion. Importantly, due to 

technical issues, this participant did not have baseline MRS or DTI measures and 
therefore did not overly influence correlation results with those metrics. 
 
Magnetic Resonance Spectroscopy.  
Proton 1H MRS data was collected in two ROIs (left Pars and left Hipp). MRS data from 
our third ROI (IPL) was not collected due to time constraints in the scanner. During the 
second MRI session we duplicated voxel placement based on images from the first MRI 
session. All GABA and Glx concentrations were analyzed using GANNET 3.1, which is a 
specialized toolbox for Matlab designed to analyze GABA by calculating the area under 
the curve. The E/I ratio of Glx to GABA within ROIs was calculated (Glx/GABA+, both 
CSF-corrected with a water reference file). This ratio measured the excitatory/inhibitory 
balance within the ROI at both the pre-tACS and post-tACS MRI sessions. Two 
participants had poor shimming at baseline and were excluded from analyses, resulting 
in usable datasets from 11 participants for these analyses. 
 
Diffusion Weighted Imaging.  
DTI data was preprocessed using FMRIB's Diffusion Toolbox (FDT 
fsl.fmrib.ox.ac.uk/fsl/fslwiki/FDT), a part of Functional MRI of the Brain software (FSL; 
Analysis Group, FMRIB, Oxford, United Kingdom). We first removed non-cortical tissue 
with the Brain Extraction Tool within FSL. To correct for head movement and eddy 
current distortions, we used Eddy Correct. Next, we used DTIfit to calculate fractional 
anisotropy (FA) maps for each participant. The FA maps were input in to Tract-based 
Spatial Statistics (TBSS) in order to create a mean FA skeleton by aligning to a common 
space (FMRIB58_FA; FA > 0.2 threshold). We analyzed individual white matter tracts 
generated with the Johns Hopkins University white matter atlas included with FSL. As 
we did not expect significant change in FA in a month, we only report the results of the 
pre-tACS baseline DTI scan. 
We selected four specific white matter tracts that serve our functional ROIs 
(Pars, IPL, Hipp). First, we selected the Fornix (FX) as it serves as the dominant outflow 
tract of the hippocampus. Second, we selected the Arcuate Fasciculus (AF) as it 
connects the frontal and temporal lobes by passing through the parietal lobe, therefore 
acting as an important tract for the IPL and Pars ROIs. Third, we selected the Superior 
Longitudinal Fasciculus (SLF) as it directly connects the IPL and Pars ROIs. Fourth, we 
selected the Uncinate (UN) as it connects the Pars and Hipp ROIs.  
 
Electrical Field Modeling.  
Current modeling of the tACS was performed using the Realistic vOlumetric Approach to 
Simulate Transcranial Electric Stimulation (ROAST)  software toolbox for Matlab to map 
electrical field (EF) changes throughout the cortex. ROAST is an open-source MATLAB-
based, automated pipeline that applies SPM segmentation to the head and neck. 
Following segmentation, typical isotropic electrical conductivities are assigned to the 
tissues and electrodes, typical boundary conditions are assigned to the surfaces, and 
simulation of current flow is achieved by solving the Laplace equation (∇∙(σ∇V) = 0), 
where V is potential and σ is conductivity. Current modeling was conducted on the skull-
striped cortex of each participant’s baseline T1 and T2 scan then fit to the MNI-152 
standard head.  
 
Exploratory Neural Analyses.  
To measure changes in neural metrics, we assessed changes in RSFC (pairwise 
connectivity between Pars, Hipp, and IPL ROIs), and MRS-based E/I within in voxels of 
interest (Pars and Hipp). Changes in neural measures were assessed with non-

parametric Wilcoxon signed-rank tests. To link behavioral tACS changes with underlying 
neural changes, we conducted correlations between the outcome metrics and neural 
metrics that had significant changes in the prior analyses. All correlation analyses were 
conducted using non-parametric Spearman’s correlations (rho).  
 
References 
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Liu, Q. et al. Intracranial alternating current stimulation facilitates neurogenesis in 
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Viskontas, I. V., Knowlton, B. J. & Fried, I. Responses of neurons in the medial 
temporal lobe during encoding and recognition of face-scene pairs. 
Neuropsychologia (2016) doi:10.1016/j.neuropsychologia.2016.07.014. 
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Wais, P. E., Arioli, M., Anguera-Singla, R. & Gazzaley, A. Virtual reality video 
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