tDCS course Chapter 4 Beyond the Brain - #26 - June 21, 2025

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Welcome back to the Neurostimulation podcast.

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I'm Dr.

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Michael Passmore, clinical associate

professor in the Department of

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Psychiatry at the University of

British Columbia in Vancouver, Canada.

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Today's episode is a continuation

on the course on transcranial

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direct current stimulation or tDCS.

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This is a course that is following

the textbook on tDCS called The

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Practical Guide to Transcranial

Direct Current Stimulation.

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This is a foundational reference for

clinicians and researchers alike.

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So whether you are a neuromodulation

specialist, a graduate student, a

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researcher, or a curious clinician,

we're going to continue in our

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exploration of this textbook to learn

how tDCS works, starting with the

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physics that it's based on, all the way

through to its physiological effects,

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and ending up with a look to see

where this exciting field is headed.

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In today's episode, we're going

to explore how direct current, or

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DC stimulation has expanded well

beyond traditional transcranial

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neurostimulation methods from the brain

to the spinal cord and the cerebellum.

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DC-based neuromodulation is moving

into new clinical frontiers, and

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we're here to unpack it together.

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So let's start with what do we

mean by DC-based neuromodulation?

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When people hear tDCS or transcranial

direct current stimulation, they usually

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think of stimulation applied to the

scalp to influence cortical excitability.

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This is correct, but in fact,

non-invasive d DC stimulation

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encompasses more than just tDCS.

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This chapter is going to introduce

us to three primary targets

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of DC based neurostimulation.

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The first is tDCS, which is

applied over the cerebral cortex.

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The second is cerebellar DC stimulation,

which is applied over the cerebellum,

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and the third is transcutaneous

spinal DC stimulation, or tsDCS,

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which is applied over the spinal cord.

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Each targets a different part of

the nervous system with unique

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applications and protocols.

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Now let's talk about the electrodes.

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So this is the interface between the

device that generates the electricity,

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the direct current in this case, and the

nervous system that's being affected.

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The essential setup includes the

target electrode, which directs the

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stimulation and the return electrode,

which completes the circuit.

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The electrode design matters whether

it's metal, conductive rubber, or

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plastic filled with saline or gel.

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Electrode size and placement significantly

affects current density and the

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resulting stimulation's focality.

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One key point is that small electrodes

allow more focused stimulation,

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potentially improving precision for

things like selective muscle activation

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or task specific motor rehabilitation.

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Let's look at the foundational method now.

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tDCS remains the most researched

and widely used form of

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non-invasive DC neurostimulation.

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It delivers a low amplitude

sustained current to the scalp

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to modulate brain activity.

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The most common electrode montage

or placement on the scalp is the

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anode electrode over the motor cortex

and the cathode electrode over the

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contralateral or opposite supraorbital

area, the area above the orbit or eye.

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tDCS is widely applied for treatment

of conditions like depression.

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It's showing promise in treatment

of aspects of stroke rehabilitation,

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as well as in cognitive enhancement.

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But tDCS isn't alone in this game anymore.

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Let's look at another one, the second

in our list, cerebellar DC stimulation.

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Why stimulate the cerebellum?

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The cerebellum is situated here at

the base of the brain at the back.

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It's at the top of the spinal

cord and underneath the

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occipital lobes of the brain.

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And the cerebellum is important

because of three main things.

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It's involved in the modulation

of motor control, so it helps

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to smooth out coordination

and the fluidity of movements.

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Dexterity is really important for

cerebellar control, as it is in

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regulating balance and coordination when

we're doing complex motor activities.

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But it's also involved in modulation

of cognitive processes as well

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as in emotional processing, which

a lot of people don't realize.

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Cerebellar tDCS has therefore been

tested for treatment of such conditions

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as ataxia or instability while walking.

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Interestingly, because of the cerebellar

role in things like emotional control

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and emotional processing, cerebellar

tDCS has been tested in conditions

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like bipolar disorder, which obviously

involves instability of mood control.

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Other conditions that cerebellar

tDCS has been tested in include

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obsessive compulsive disorder or

OCD and chronic pain conditions.

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The electrode placement or montages

in these variable applications

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typically place the active electrode

over the midline or on one cerebellar

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hemisphere with the return electrode

on the shoulder or the cheek.

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Clinical studies are showing promise.

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For instance, cerebellar tDCS was

shown to improve sleep in bipolar

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disorder patients, and it's also been

shown to help alleviate obsessive

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compulsive disorder symptoms.

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Now let's look at spinal

cord stimulation or tsDCS.

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The spinal cord may seem like

an unlikely target for surface

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non-invasive neurostimulation.

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But tsDCS appears to work.

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Cathodal or anodal current over the

thoracic or cervical spine can alter

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things like segmental reflexes, pain

perception, and motor unit recruitment.

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Potential clinical applications include

things like treatment of restless

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leg syndrome, spinal cord injury,

and motor neuron excitability in

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conditions like ALS Amyotrophic lateral

sclerosis, otherwise known as Lou

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Gehrig's Disease or Multiple Sclerosis.

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Placement or montages of electrodes, can

vary with the return electrodes on places

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like the shoulder, the abdominal wall, or

the vertex, the very tip top of the head,

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depending on the desired spinal target.

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Now, what about home-based applications

and the democratization of tDCS

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and these other non-invasive

neurostimulation treatments?

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Unlike rTMS or repetitive

transcranial magnetic stimulation, DC

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current-based methods are portable,

affordable, and can be safe for

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home use with clinical supervision.

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Many studies have validated remote

supervision protocols for treatment of

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things like psychosis, stroke, tinnitus,

and symptoms of multiple sclerosis.

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This opens the door for remote scalable

treatment options, including in areas

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like neurorehabilitation, even in

remote or underserved communities.

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However, a word of caution,

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the simplicity of tDCS also makes

it potentially easy to misuse.

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This means that medical supervision

and standardized treatment protocols

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will be essential to ensure that

these treatments can be used

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safely and targeted appropriately.

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Now let's look at some

clinical applications and

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consider some case highlights.

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Let's run through a few

case-based examples.

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What about bipolar disorder?

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Well, studies have shown that cerebellar

tDCS can improve symptoms like sleep

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and improve function during the day.

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It has been studied in conditions like

Parkinson's disease where tDCS has

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been shown when applied over the motor

cortex or cerebellum to improve movement

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disorder subscores in certain patients.

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In depression, prefrontal

cerebellar montages has been shown

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to lead to symptom improvements

in treatment resistant patients.

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These kinds of studies underscore

the importance of target selection,

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polarity and protocol duration, as

well as the need for development of

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personalized approaches to treatment.

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Let's look at some challenges and look

ahead to see what's on the frontier.

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Despite these kinds of studies that

show exciting progress, there are

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certain key challenges that remain.

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The first is the lack of consistent

standardized protocols across research

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sites, which is still in development,

and hopefully we will be getting some

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more consensus on that, that can be

incorporated into clinical practice

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guidelines in the near future.

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The second is high inter-individual

variability, which on the one hand needs

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to be reinforced by replicated studies

in large populations, but on the other

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hand can underscore the importance of

personalization and how these treatments

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might be part of a comprehensive approach

to treatment of individual situations.

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Perhaps not just with neurostimulation,

but in addition to other treatments

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like physical therapy, pharmacotherapy,

counseling, so that an individual person

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can take advantage of multiple different

treatment options in order to get

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the best benefit for their particular

situation at that given point in time.

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The third is the need for focal targeting

and modeling of the specific electrical

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current that's being delivered.

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These lead to ongoing questions around

dose response and optimal frequency

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of treatment in terms of the duration

and the total course, the length

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of the course of each specific.

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This includes factors such as

specific electrical dose response

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relationships, as well as the optimal

frequency and duration, not only of

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individual sessions, but of entire

courses of treatment in terms of the

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neurostimulation that's being offered.

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And so here's where modeling and

things like closed loop systems and

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even artificial intelligence assisted

protocols can play an increasingly

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important role over the next years.

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So in closing, non-invasive DC based

neuromodulation is certainly evolving.

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From lab bound protocols to home-based

remote supervised use things like

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tDCS, cerebellar DC stimulation,

and tsDCS, spinal cord stimulation

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may soon represent a triad of tools

for neurologic and psychiatric care,

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as well as in other fields like

physical medicine and rehabilitation.

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These therapeutic options

are simple to use.

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They're low cost and scalable,

potentially accessible to people who

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are in underserviced and more remote

areas, and therefore they can be

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potentially transformative in terms

of improving health and wellness.

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Thanks again for tuning in.

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I hope that you enjoyed today's episode.

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Please be sure to like and subscribe.

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Leave a comment or a review.

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Ask questions in the

comment section below,

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and don't forget to share this episode

with someone that you think might be

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interested in the discussion that we

had today, as well as in joining us on

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our exploration of this tDCS textbook

so that we can continue to learn all

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about this revolutionary technology

and how it will hopefully be beneficial

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for many people in the coming years.

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Also let us know if you have any

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would like to be explored on the show.

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Until next time, thanks

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So stay well, stay curious,

and we'll see you next time on

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the Neurostimulation Podcast.