Effects of tDCS on Precision of Finger Force Control and Rhythmic Tapping Movements ... and participants continued tapping at the same rate for 40s. 6.5. 7. 7.5.
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 Harrigian1,2, Nikita Kuznetsov3, & Dagmar Sternad2,3,4 Departments of Mathematics1, Physics2, Biology3, and Electrical and Computer Engineering4, Northeastern University
Motor Cortex
1 mA anodal stimulation over the motor cortex (C3-Fp2 location) using saline soaked sponges (35cm2).
2 mA cathodal stimulation over the right cerebellum for using saline soaked sponges (25cm2).
0.706 V/m
1
7.5
8 Time (s)
8.5
9
9.5
Dependent Measures: Standard deviation of inter-tap interval (ITI) during continuation tapping.
Experiment 1: Motor Cortex Stimulation
Experiment 2: Cerebellum Stimulation 5 minute rest
5 minute rest
Practice 30 Trials
Block 1 25 Trials Sham
Block 2 25 Trials Sham
Control Group
Practice 12:4
Block 1 9:3 Sham
Block 2 9:3 Sham
tDCS Group
Practice 30 Trials
Block 1 25 Trials Sham
Block 2 25 Trials tDCS
tDCS Group
Practice 12:4
Block 1 9:3 Sham
Block 2 9:3 tDCS
20 minute stimulation
10 minute stimulation
10 minute 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.
Discussion Lack of tDCS effect on variability of isometric force may be due to high inter-individual variability or too short stimulation duration. State-dependence of stimulation: force production may interfere with tDCS. Visualization of the resulting current distribution within a single individual’s brain (Bonsai, http://neuralengr.com)
tDCS
Sham
tDCS
Sham
0.15 0.1
0.05 0
Sham Control
5 minute rest
Control Group
20 minute stimulation
With visual feedback
Increase in variability with tapping is consistent with the noise hypothesis: cerebellum normally inhibits motor cortex, and cathodal stimulation reduced that inhibition.
Without visual feedback
0.15 0.1 0.05
0
tDCS
7
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.
5 minute rest
tDCS tDCS
Results Exp-2: Cerebellar Montage
0 6.5
Cerebellum
Sham Control
Sham
tDCS Montage
0
Sham
H2: Stimulation of the cerebellum (E2) increases timing variability during finger tapping.
0.05
No statistically significant change in force variability with visual feedback and without visual feedback.
Inter-tap interval
2
0.1
Sham
H1: tDCS stimulation over the motor cortex (E1) and cerebellum (E2) increases variability of isometric finger force with and without visual feedback.
Tap Interval
3
tDCS tDCS
Force Variability (N)
2
Sham Control
0.15
Sham tDCS tDCS Control
tDCS tDCS
No statistically significant change in force variability with visual feedback and without visual feedback.
*
60 40 20 0
20
t(26) = 2.07, p=.048
Sham Control
tDCS tDCS
ITI Variability Change (%)
Time
1.5
0
Without visual feedback
Force Variability (N)
Dependent Measures: Standard deviation of finger force during visual feedback and without visual feedback segments of the trial.
0.05
tDCS
1
12
tDCS
0.5
10
Sham
0
8
Sham
Signal Magnitude
50
We conjectured that in addition to changing the spontaneous rate of neural activity, tDCS also increases “neural noise.”
6 Time (s)
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.
Hypotheses 100
4
Sham
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).
2
0.1
Sham
Neural activity increases under the anode and decreases under the cathode.
1 0 0
Force (N)
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).
No Visual Feedback (5s)
0.15
Sham Sham
Baseline Level
Visual Feedback (5s)
2
Force Variability (N)
Online Feedback
3
Force Variability (N)
Force (N)
Target Level
With visual feedback
Sham
4
Sham
Visual Display
Inter-tap Interval Variability (ms)
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).
Results Exp-1: Motor Cortex Montage
Sham
Experimental Tasks and Design
Sham
Background
*
t(26) = 2.14, p=.041
10 0
-10 -20
Sham
tDCS
Control tDCS
Variability of inter-tap interval increased. 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), 206223. 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.
