tDCS course Chapter 8 tDCS Stimulation Parameters - #33 - Sept 6, 2025

Mike: 00:00:10

Welcome to the Neurostimulation Podcast.

2

: 00:00:12

I'm Dr.

3

: 00:00:12

Michael Passmore, clinical associate

professor in the department of

4

: 00:00:16

psychiatry at the University of

British Columbia in Vancouver, Canada.

5

: 00:00:21

The Neurostimulation Podcast

is all about exploring the

6

: 00:00:23

fascinating world of clinical

neurostimulation and neuroscience.

7

: 00:00:28

We have discussions with clinicians

and researchers in the field.

8

: 00:00:32

And in this episode, we're going

to unpack chapter eight of the

9

: 00:00:35

textbook called Practical Guide to

Transcranial Direct Current Stimulation.

10

: 00:00:40

The title of chapter eight is Stimulation

Parameters and Their Reporting.

11

: 00:00:45

But if that sounds kind of dry, stick

with me because this is the part of

12

: 00:00:48

tDCS that makes or breaks good science.

13

: 00:00:59

Think about it this way, if you and I

both run a tDCS session at 2 mA, are

14

: 00:01:04

we actually doing the same experiment?

15

: 00:01:06

The answer is probably not, and

that's the heart of the problem.

16

: 00:01:11

What seems like a simple setting is really

just one piece of a much bigger puzzle.

17

: 00:01:15

Today we're going to explore what those

pieces are, why they matter, and why

18

: 00:01:19

reporting them clearly is essential.

19

: 00:01:22

So what exactly counts as a parameter, and

what do we mean by stimulation parameters?

20

: 00:01:28

It's really everything that

defines a session of tDCS.

21

: 00:01:32

Everything from the electrodes,

including their size, shape, and

22

: 00:01:36

even the material that they're made

of the placement on the scalp, or in

23

: 00:01:40

other words, which montage that you

use and how precisely it's applied.

24

: 00:01:45

And then there's the current intensity

and polarity, not just how strong,

25

: 00:01:49

but which way the current flows.

26

: 00:01:52

And then there's the duration of

stimulation, including whether you ramp

27

: 00:01:55

it up slowly or switch it on suddenly.

28

: 00:01:58

And that's not all.

29

: 00:02:00

There are also protocol related factors,

how you prepare the skin, whether

30

: 00:02:04

you run tDCS while someone is doing

a task simultaneously, and how many

31

: 00:02:10

sessions in total that they receive.

32

: 00:02:13

Here's an analogy.

33

: 00:02:14

Imagine baking bread.

34

: 00:02:16

If I just tell you, I baked bread

at 350 degrees for 30 minutes.

35

: 00:02:20

You don't know if I used wheat flour

or rye yeast or sourdough starter.

36

: 00:02:25

The same goes for tDCS.

37

: 00:02:27

Without the full recipe, you

can't reproduce the results.

38

: 00:02:32

This brings us to why reporting

parameters in studies is so critical.

39

: 00:02:36

One of the biggest issues in

the field is that studies don't

40

: 00:02:39

always report all the details.

41

: 00:02:41

So when another lab tries to replicate

the experiment, they might not

42

: 00:02:45

actually be doing the same thing.

43

: 00:02:47

And in science,

reproducibility is everything.

44

: 00:02:50

Here's a striking example.

45

: 00:02:52

Two studies might both say that they

used 2 mA of tDCS current, but if

46

: 00:02:57

one used a big sponge electrode and

the other a small high definition

47

: 00:03:00

electrode, the current density in the

brain could be completely different.

48

: 00:03:04

That means the results aren't

directly comparable, even though

49

: 00:03:08

that they look the same on paper.

50

: 00:03:09

Okay.

51

: 00:03:10

That's why consensus efforts,

like CONSORT style reporting

52

: 00:03:13

guidelines are so important.

53

: 00:03:15

They push researchers to

list everything clearly.

54

: 00:03:18

Electrode size, placement

polarity, current density,

55

: 00:03:23

duration, ramp times participant

characteristics, even side effects.

56

: 00:03:29

So this level of transparency

doesn't just help replication, it

57

: 00:03:32

builds trust in the entire field.

58

: 00:03:35

Let's look at some challenges

in the parameter space.

59

: 00:03:39

This is the huge range of

possible combinations of things

60

: 00:03:42

that we just talked about.

61

: 00:03:43

Electrode sizes, shapes,

positions, currents, and durations.

62

: 00:03:48

It's almost infinite to be honest,

and that means early studies

63

: 00:03:52

often oversimplified things.

64

: 00:03:54

They treated all tDCS as if it was the

same, but we now know that tiny tweaks

65

: 00:03:59

in the setup can make big differences.

66

: 00:04:01

On top of that, there's

inter-individual variability.

67

: 00:04:05

Your skull thickness, the folds

of your cortex, even the amount of

68

: 00:04:08

the cerebral spinal fluid around

your brain can all change how much

69

: 00:04:12

current actually reaches the neurons.

70

: 00:04:16

So the challenge is how do we make sense

of this huge, messy parameter space?

71

: 00:04:20

This is where computational modeling,

which we're going to cover in chapter

72

: 00:04:24

nine, starts to play a crucial role.

73

: 00:04:28

Now let's talk about practical guidelines.

74

: 00:04:30

So what should researchers

and clinicians actually do?

75

: 00:04:33

Well, chapter eight of our textbook

lays out some practical guidelines,

76

: 00:04:37

and at a minimum, every report

should include the following.

77

: 00:04:40

Electrode size, shape, and material.

78

: 00:04:42

Exact scalp placement, ideally,

exact scalp placement, ideally

79

: 00:04:48

using standardized coordinate

systems, current intensity,

80

: 00:04:52

polarity and density, stimulation,

duration, and ramping protocol,

81

: 00:04:59

contextual details.

82

: 00:05:01

Was stimulation applied during rest or

was the participant performing a task?

83

: 00:05:06

Don't forget reporting on

tolerability, side effects and

84

: 00:05:10

participant characteristics.

85

: 00:05:11

Even small details can help

others understand why the results

86

: 00:05:15

turned out the way that they did.

87

: 00:05:17

Think of this as a checklist.

88

: 00:05:18

The minimum recipe that every tDCS

paper or clinical report should contain.

89

: 00:05:24

So what's the bottom

line from chapter eight?

90

: 00:05:27

First parameters are like the recipe for

brain stimulation when it comes to tDCS.

91

: 00:05:32

Second is that small differences in those

parameters can completely change outcomes.

92

: 00:05:37

Third is that transparent,

consistent reporting is what

93

: 00:05:40

makes science reproducible and

clinical practice safe in tDCS.

94

: 00:05:46

The details aren't just

technicalities, they are the science.

95

: 00:05:50

That's it for today's episode.

96

: 00:05:52

Next time we'll dive into chapter

nine, where we'll see how computational

97

: 00:05:55

modeling helps us to make sense of

this complex parameter space and

98

: 00:06:00

moves us toward personalized dosing.

99

: 00:06:02

Thanks again for joining me today

on the Neurostimulation Podcast.

100

: 00:06:06

I really appreciate your time,

your interest, and your attention.

101

: 00:06:10

If you think that someone you know

might be interested in this episode,

102

: 00:06:13

please forward it on to them and

leave your comments or questions

103

: 00:06:17

in the comments section below.

104

: 00:06:19

Until next time be well, stay

curious and I'll see you again

105

: 00:06:22

on the Neurostimulation Podcast.