Effects of tDCS on Precision of Finger Force Control and Rhythmic Tapping Movements.

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Undergraduate
Physical and Life Sciences
Bachelors of Science
Abstract ID# 579
Effects of tDCS on Precision of Finger Force Control and Rhythmic Tapping Movements
Keith Harrigian
1,2
, Nikita Kuznetsov
3
, & Dagmar Sternad
2,3,4
Departments of Mathematics
1
, Physics
2
, Biology
3
, and Electrical and Computer Engineering
4
, Northeastern University
Experimental Tasks and Design
Nitsche, M. A., Cohen, L. G., Wassermann, E. M., Priori, A., Lang, N., Antal, A., ... & Pascual-Leone, A.
(2008). Transcranial direct current stimulation: state of the art 2008. Brain stimulation, 1(3), 206-
223.
Reis, J., Schambra, H. M., Cohen, L. G., Buch, E. R., Fritsch, B., Zarahn, E., ... & Krakauer, J. W. (2009).
Noninvasive cortical stimulation enhances motor skill acquisition over multiple days through an
effect on consolidation. Proceedings of the National Academy of Sciences, 106(5), 1590-1595.
Background
1 mA anodal stimulation over the
motor cortex (C3-Fp2 location) using
saline soaked sponges (35cm
2
).
2 mA cathodal stimulation over the
right cerebellum for using saline
soaked sponges (25cm
2
).
tDCS is a non-invasive and safe technique for brain neuromodulation that
can increase or decrease spontaneous level of neural activity in the brain
in a montage-specific way (Nitsche et al., 2008).
tDCS Montage
H1: tDCS stimulation over the motor cortex (E1) and cerebellum (E2) increases
variability of isometric finger force with and without visual feedback.
H2: Stimulation of the cerebellum (E2) increases timing variability during finger
tapping.
Target Level
Baseline Level
Online Feedback
Dependent Measures: Standard deviation of finger force during visual
feedback and without visual feedback segments of the trial.
Results Exp-1: Motor Cortex Montage
0
0.05
0.1
0.15
Sham tDCS
Sham
tDCS
Control
tDCS
0
0.05
0.1
0.15
Sham tDCS
Sham
tDCS
Sham
Sham
Control
tDCS
Force Variability (N)
With visual feedback Without visual feedback
No statistically significant change in force variability
with visual feedback and without visual feedback.
Force Variability (N)
Sham
Sham
Visual Display
Task 1: Participants reached the target force level (3N) as fast as possible
and maintained it for 10s, first with visual feedback and then without.
Anodal tDCS delivered to the primary motor cortex promotes long-term
retention of skill on tasks involving precision and timing of finger control
(Reis et al., 2009).
Motor Cortex Cerebellum
Hypotheses
Experiment 1:
Motor Cortex Stimulation
Experiment 2:
Cerebellum Stimulation
Participants: 24 healthy right-handed young adults (22.0±2.4 yrs) in Exp-1.
28 healthy right-handed young men (20.9±3.7 yrs) in Exp-2.
Control
Group
tDCS
Group
Practice
30 Trials
Block 1
25 Trials
Sham
Block 2
25 Trials
Sham
Practice
30 Trials
Block 1
25 Trials
Sham
Block 2
25 Trials
tDCS
5 minute rest 5 minute rest
20 minute
stimulation
20 minute
stimulation
Control
Group
tDCS
Group
Practice
12:4
Block 1
9:3
Sham
Block 2
9:3
Sham
Practice
12:4
Block 1
9:3
Sham
Block 2
9:3
tDCS
5 minute rest 5 minute rest
10 minute
stimulation
10 minute
stimulation
Task 2: Participants synchronized with auditory metronome (800ms
period) for 10 beats by tapping on the force sensor. The beats terminated
and participants continued tapping at the same rate for 40s.
6.5 7 7.5 8 8.5 9 9.5
0
1
2
3
Time (s)
Force (N)
Tap Interval
0 2 4 6 8 10 12
0
1
2
3
4
Time (s)
Force (N)
Visual Feedback
(5s)
No Visual Feedback
(5s)
Visualization of the resulting
current distribution within a
single individual’s brain
(Bonsai, http://neuralengr.com)
0.706 V/m
Discussion
Lack of tDCS effect on variability of isometric force may be due to high
inter-individual variability or too short stimulation duration.
Increase in variability with tapping is consistent with the noise hypothesis:
cerebellum normally inhibits motor cortex, and cathodal stimulation
reduced that inhibition.
Dependent Measures: Standard deviation of inter-tap interval (ITI)
during continuation tapping.
Inter-tap
interval
*
Results Exp-2: Cerebellar Montage
No statistically significant change in force variability
with visual feedback and without visual feedback.
0
0.05
0.1
0.15
Sham  tDCS
Sham
Sham
tDCS
Sham
Control tDCS
0
0.05
0.1
0.15
Sham  tDCS
Sham
Sham
tDCS
Sham
Control tDCS
Force Variability (N)
With visual feedback Without visual feedback
Force Variability (N)
0
20
40
60
Sham  tDCS
Sham
Sham
Control
tDCS
tDCS
Sham
-20
-10
0
10
20
Sham tDCS
Control tDCS
Inter-tap Interval
Variability (ms)
Variability of inter-tap interval increased.
ITI Variability
Change (%)
*
Transcranial direct current stimulation (tDCS)
is currently being explored as a promising new
tool for movement rehabilitation (stroke,
Parkinson’s disease, dystonia) and for
enhancement of motor performance (video
gamers, musicians, soldiers).
We conjectured that in addition
to changing the spontaneous
rate of neural activity, tDCS also
increases “neural noise.”
0.5 1 1.5 2
0
50
100
Time
Signal Magnitude
Neural activity increases under the anode and decreases under the cathode.
t(26) = 2.14, p=.041
t(26) = 2.07, p=.048
State-dependence of stimulation: force production may interfere with tDCS.