tDCS course Chapter 7 tDCS Methodology & Protocols - #30 - July 20, 2025

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In today's episode, we're going to review chapter seven of the

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Practical Guide to Transcranial Direct

Current Stimulation, Principles,

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Procedures, and Applications.

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Chapter seven is going to involve

an analysis of the methodological

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considerations for selection.

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Of tDCS approach.

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In chapter seven, we're going to look

at the methodological considerations for

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selection of tDCS approach protocols and

devices In this review of chapter seven,

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we're going to look at methodological

considerations for selection of

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transcranial direct current stimulation

approach protocols and devices.

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So we're going to look at how to

do tDCS properly: Protocol, device,

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and design decisions that matter.

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Today's episode is going to involve

a deep dive into an important topic,

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but one that's often overlooked

areas of tDCS methodology.

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How can you set up a tDCS research

study or a clinical session?

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The way that you set up your tDCS

research study or clinical session

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can make or break your results.

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So let's explore what goes into choosing

the right approach, whether you're

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working in a lab, a clinic, or exploring

home-based remote supervision use.

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So why does methodology matter in tDCS?

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It might seem like tDCS is a simple

tool, two electrodes, low current and go.

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But in reality, the effectiveness

and replicability of tDCS depends

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on a long list of factors.

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Things like electrode size and placement,

stimulation, intensity, and duration.

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Session frequency and course

duration, and whether stimulation

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is applied during a task or at rest.

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Even minor changes in these variables

can lead to different outcomes, and

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that's why evidence-based and carefully

considered protocol design is essential.

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So let's look at the tDCS decision matrix.

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The chapter introduces a decision

making framework that includes

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questions like: Is tDCS indicated

for this particular patient?

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What polarity should be

used and anodal or cathodal?

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What montage or placement of

electrodes and what electrode

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size is going to be optimal?

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Is the stimulation uni

site by site or multi-site?

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What frequency and duration of

treatment is going to be best?

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This is all visualized in a clinical

decision tree, which is figure 7.5

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in the textbook, and we'll show that here.

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And this guides the clinician

from the clinical question

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through to the protocol selection.

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So now we're going to define the

goal: research enhancement or therapy.

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So the protocol should begin

with identifying your goal.

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Are you trying to explore cortical

function in a research setting?

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Are you trying to enhance cognition

or motor skills in a neuro enhancement

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or neuro rehabilitation setting?

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Or are you trying to treat a condition

like depression or again, stroke

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recovery in a therapeutic sense?

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Each of these goals comes

with a different design need.

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For example, cognitive enhancement might

benefit from short repeated sessions

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where rehabilitation might require

longer high frequency type protocols.

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So what are some key

variables in protocol design?

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Let's talk about the big dials,

so to speak, that you can adjust.

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The first is electrode size and

placement smaller electrodes is

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going to equal greater ality.

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It's not hard to imagine that if you

have a smaller electrode with a smaller

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scalp contact, it's going to lead to a

greater vocality of electrical current.

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Larger electrodes, on the other

hand, are going to lead to a

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more diffuse current application.

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The second is stimulation site,

which we're going to choose based

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on the network activity and not

just that underlying neuroanatomy.

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Remember, no brain region

works in isolation.

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The third is montage,

type, montage or placement.

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There's cephalic, so-called

cephalic, C-E-P-H-A-L-I-C, which

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is both electrodes on the head.

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There's extra cephalic, which is

involving a return electrode on another

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part of the body, like on the shoulder

or arm, and there can be dual site or

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multi-site for complex network modulation.

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The fourth is timing.

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So online during a task, like a motor

task, a learning task, an emotional

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task, or some other sort of activity that

a person's doing in terms of movement

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or thinking or feeling versus offline,

which would be before or after a task.

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So stimulation before or after a

task, but technically at rest online

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appears to yield stronger behavioral

effects in the studies that are.

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Considering differences here online

appears to yield stronger behavioral

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effects in those particular studies

that are looking at differences in

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terms of online versus offline effects.

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Now let's have a look at standalone

tDCS versus adjunctive tDCS.

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So tDCS by itself versus

tDCS in combination with

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another treatment modality.

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This is a question, should tDCS be used

by itself, or is it best when paired

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with something else, or even multiple

other treatment options at the same time?

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Examples could include pain management.

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Pain management, is it best with tDCS

alone or in combination with other

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types of pain management strategies?

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Stroke rehabilitation, perhaps

using combinations of tDCS

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and active physiotherapy.

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Depression treatment, perhaps using

tDCS in combination with medications

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like SSRIs and/or psychotherapy,

like cognitive behavioral therapy.

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So remember, when we're combining

treatments, we want to use factorial

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designs in order to test for synergy

between combined treatment modalities

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like was used in the so-called select

tDCS trial for treatment of depression.

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Now let's look at some population

specific considerations.

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Certain special populations require

even more tailored protocols.

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For example, children with smaller

heads is going to involve an

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inherently different current flow.

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So use of lower intensities and close

monitoring for side effects will be

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important in older adults because of the

cortical atrophy that occurs during aging,

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that leads to a greater gap between the

outer surface of the cortex and the inner

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surface of the skull so that there's more

CSF or cerebrospinal fluid, outside of

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the brain bathing the brain, that can

lead to altered current distribution in

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terms of direct current emanating from

the electrode on the outside of the scalp,

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traveling through the scalp, then through

the tissues that are underneath the scalp,

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the so-called dura through the CSF, and

eventually to the cerebral cortex itself.

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This may require different electrode

montages or longer ramp times.

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What about certain neurologic

or psychiatric conditions?

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Well, custom electrode placement

may improve outcome in a

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condition dependent manner.

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So for example, monitoring for medication

interactions or symptom fluctuation

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during tDCS can lead to descriptions

that might be important in terms of

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identifying commonalities that can then

be integrated into treatment protocols.

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Now let's look at some differences between

clinic-based versus home-based device use.

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Certified tDCS devices fall

into two main categories.

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There are clinic-based devices, which

are typically programmable, often used

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in clinical trials or in hospitals or

outpatient clinics, and then there are

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home-based devices, which typically

will be also programmable but then

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once they're programmed, the settings

are locked to prevent people from

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interfering with the clinically prescribed

and carefully selected settings.

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And the use then is often remotely

supervised via telehealth or another way

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of the patient staying in contact with the

practitioner and in order to provide real

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time assistance and direction in terms of

the setup and in order to make sure that

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the device is being used in a safe manner.

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So for selecting a device, it's important

to consider things like the stability of

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the current that's being delivered, the

ramp features, so the ramp being the,

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the intensity of the current from zero

current, all the way up to the prescribed

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full current and how long that takes.

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And then on the other hand,

when the session is finished,

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when the ramp is going from the

full current down to zero again.

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So electrode impedance checks to make

sure that the actual contact between the

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electrode and the scalp is optimized.

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And then in research studies appropriate

blinding capabilities for sham treatments

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to compare with actual treatments.

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Now let's have a look at the

session frequency and repetition.

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So how often should tDCS be delivered?

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The old rule was longer is better, but

research has really shown that excessively

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long stimulation may actually trigger

homeostatic counter anti-regulation.

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So the brain is a homeostatic, the nervous

system, you know, altogether, and really

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you could expand that to say that the body

altogether is a homeostatic system: If

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there's a change, the brain in particular

will seek to counteract that change

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in order to maintain a balanced state.

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So studies showed that excessively

long tDCS stimulation is potentially

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going to trigger the brain's response

in terms of a homeostatic counter

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reregulation, which may in the end

kind of undo the positive therapeutic

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effects of shorter stimulation with tDCS.

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So instead, in order to find the sweet

spot in between those two states, the

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normal state where there are target

symptoms, and the excessive tDCS state,

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where the brain kind of counteracts

what the tDCS is trying to do in a

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therapeutic sense, what is being shown

is that repeated shorter tDCS sessions

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over the course of a day, is inducing

more robust therapeutic effects.

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And so this is what's known as within

session repetition, and it can produce

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effects that are lasting up to 24

hours in one particular session time.

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What about integration

with behavioral tasks?

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So it's becoming clear that when

you combine tDCS with certain

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tasks, amazing things can happen.

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For example, faster learning,

greater retention of information

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and improvement of mood.

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But there is also a flip side.

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Certain studies are showing a

potential interference between

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stimulation and task performance

if it's poorly timed or mismatched.

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So what appears to be important

is to align the task, type,

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the stimulation target, and the

session schedule very carefully.

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So some final thoughts.

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It's important to look at this

as a methodological toolbox.

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Designing effective tDCS protocols appears

to be a combination of art and science.

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You need to match your stimulation

parameters to your goal.

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You need to consider the

population that you're treating.

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You need to choose devices and

montages or electrode placements.

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That are based on feasibility

and scientific rigor.

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You need to test and refine through

careful measurement and reporting.

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If it's a study and the more

standardized and transparent our

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methods are going to be, the faster

the field will be able to move forward.

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And for research protocols, obviously

it's important to test and refine through

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careful measurement and reporting.

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So the more standardized and transparent

that our methods are, the faster

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that the field will move forward.

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Thanks again for joining me for this

deep dive into tDCS methodology.

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Whether you're a researcher or a

clinician or someone who's just curious

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about how this is being done, it's

important to remember that how you set

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up your stimulation protocol matters as

much as whether you stimulate at all.

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Just a quick reminder to please

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So until next time, don't forget

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and I will see you there.

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Please stay well, stay curious.

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