Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that uses low direct current delivered through electrodes placed on the scalp to modulate cortical excitability. Several studies reviewed found that anodal tDCS over the affected motor cortex and cathodal tDCS over the unaffected motor cortex improved motor performance in stroke patients. Parameters like current dosage, electrode size and position, and stimulation duration need to be defined to induce different physiological effects. tDCS shows promise as a treatment for stroke rehabilitation and other neurological conditions by enhancing or inhibiting neural activity in targeted brain regions.

1. Transcranial Direct Current Stimulation
(tDCS) in Stroke Rehabilitation
By
Md. Kafiul Islam
Jan 26, 2013
A Literature Review

2. Introduction
• What is tDCS
– Non-invasive, painless brain stimulation
– Constant, low-intensity DC by 2 electrodes
• Types of Stimulation
– Anodal : Excites neural activity
– Cathodal : Inhibits neural activity
• Advantages
– Cheap, non-invasive, painless and safe
– Easy to administer and equipment is portable
– Least side effect (slight itching or tingling on scalp)
Valuable tool for treatment of stroke recovery
and other neuropsychiatric conditions
• Depression, anxiety, Parkinson’s disease, and chronic pain
• Cognitive improvement

3. Introduction (Cont…)
• Stroke
– Rapid loss of brain function due to disturbance in the blood supply to the
brain
– Brain cells (Neurons) suddenly die because of a lack of oxygen
• After Effect
– Inter-hemisphere Imbalance
– Inability to move one or more limbs on one side of body
– Inability to understand or formulate speech
– Inability to see one side of the visual field

4. Paper-1 Review
Transcranial direct current stimulation: a
noninvasive tool to facilitate stroke
recovery
Arch Neurol. 2008 December

5. Review: Paper-1
UEFM: Measure of neurological and motor function.

6. Paper-2 Review
Noninvasive Brain Stimulation in Stroke
Rehabilitation
NeuroRx. 2006

7. Review: Paper-2
Review at the effects of TMS and tDCS on motor cortical function and motor
performance in healthy volunteers and in patients with stroke.
Findings:
 Both techniques have been proved to either enhance or suppress cortical excitability
 Studies of cortical plasticity after stroke suggest that the damaged cortex has the
potential for extensive reorganization

8. Paper-3 Review
Transcranial Direct Current Stimulation of the
Unaffected Hemisphere in Stroke Patients
Neuroreport. 2005

9. Review: Paper-3
Recovery of function after a stroke is determined by a balance of activity in the neural network
involving both the affected and the unaffected brain hemispheres. Increased activity in the
affected hemisphere can promote recovery, while excessive activity in the unaffected
hemisphere may represent a maladaptive strategy
• Findings
– both cathodal stimulation of the unaffected hemisphere and anodal stimulation of the
affected hemisphere (but not sham transcranial direct current stimulation) improved
motor performance significantly.
Motor performance change (%) compared with baseline after stimulation of the primary motor cortex
of the unaffected hemisphere (cathodal stimulation), stimulation of the primary motor cortex of the
affected hemisphere (anodal stimulation)

10. Paper-4 Review
Clinical research with transcranial direct current
stimulation (tDCS): Challenges and future
directions
Neuroreport. 2005

11. Paper-4 Review
TDCS dosage
(1) Current dosage (measured in amperes);
(2) Duration of stimulation; and
(3) Electrode montage (size and position of all electrodes).
Parameters of Stimulation
TDCS parameters can vary widely and several factors need to be defined. These
factors include electrode size and positioning, intensity, duration of stimulation,
number of sessions per day, and interval between sessions. By varying these
parameters, different amounts of electric current can be delivered, thus
inducing diverse physiologic effects.

12. Paper-5 Review
Excitability Changes Induced in the Human Motor
Cortex by Weak Transcranial Direct Current
Stimulation
J. Physiol. 2000

13. Review: Paper-5
Cortical excitability change during current flow
Polarity-specific after-effect of DC stimulation
Findings
 Excitation could be achieved selectively by anodal stimulation
and inhibition by cathodal stimulation
 By varying the current intensity and duration, the strength and
duration of the aftereffects could be controlled
The authors demonstrated in the intact human the possibility of a noninvasive modulation
of motor cortex excitability by the application of weak direct current through the scalp

14. Electrode Shape & Salinity
(a1 and b1): Modeled electrode-sponge finite element geometry. The head model comprised of 4 concentric blocks (skin, skull, CSF,
brain). The electrode and sponge pad had 0.5 and 2.5 mm thickness, respectively. 2 mA of total current was applied to 35 cm2 pads
(boundary current density 0.0057 A/m2).
(a2 and b2): For saline soaked sponge (1.4 S/m), current density was concentrated at electrode edges, with higher values observed
at the rectangular electrode corners. Both panels plotted to the peak current density for the rectangular electrode (0.041 A/m2).
(a3 and b3): Re-plotting these panels to a maximum current density of 0.029 A/m2, emphasize that outside of the rectangular
electrode corners, the typical current density around the circular electrode is higher.
(a4 and b4): Decreasing sponge salinity (0.05 S/m) resulted in significantly more uniform electrode current densities, and reduced
peak current densities for both rectangular and circular pads to approximately the same values
Comparison of the skin current density profiles for area matched rectangular and
circular pads

15. Electrode montage in stroke
Findings:
•Bilateral tDCS, anodal tDCS and cathodal tDCS were shown to be associated with
significant improvements on the JTT.
•Bilateral and extra-cephalic stimulation do not induce effects on motor function
•Effects of tDCS are task-dependent and might be different for neuropsychiatric
conditions, such as stroke
Changes in the main outcome (Jebsen–Taylor Hand Motor Function Test – as measured in seconds) in each electrode
montage. Columns indicate mean changes and bars indicate standard error of the mean.

16. Summary Note on tDCS
Brain function under the anodal electrode site is enhanced by roughly 20 to 40%
when the current density (concentration of amperage under the electrode) exceeds
40 μA/cm2 (260 μA/inch2). The cathode reduces brain function under the electrode
site by 10 to 30% at the fore-mentioned current density. Anodal stimulation is the
most common form of tDCS as most applications require enhanced brain function.