Associations Between Motor Cortex Inhibition and Stable Turning Characteristics in Healthy Controls and People with Multiple Sclerosis

Abstract

The current results form this on-going study highlight the cortical influence for dynamic movements. Although cSP duration was not significantly different between groups or hemispheres, significant correlations were observed for turning metrics and cSP duration for the left hemisphere in PwMS, such that greater motor cortex inhibition was associated with better turning performance which resembled the healthy control cohort. These preliminary results indicate that inhibition may be a crucial neural mechanism underlying dynamic movements that are strongly associated with fall risk. However, additional testing is needed to make more definitive claims.

Full text

DEPARTMENT OF
HEALTH & EXERCISE SCIENCE
COLLEGE OF HEALTH
AND HUMAN SCIENCES
COLORADO STATE UNIVERSITY
Associations Between Motor Cortex Inhibition and Stable Turning
Characteristics in Healthy Controls and People with Multiple Sclerosis
Clayton W. Swanson1, Sutton B. Richmond1, Andrew S. Monaghan2, Moriah R. Hanson1, Tyler T. Whittier1, & Brett W. Fling1,3
1Department of Health & Exercise Science, Colorado State University, Fort Collins, CO
2Department of Exercise & Nutrition Science, Arizona State University, Phoenix, AZ
3Molecular, Cellular, and Integrative Neuroscience Program, Colorado State University, Fort Collins, CO
P1-V-168
Figure 3. Linear regressions for left hemisphere cSP duration and turn
variables: (A) Turn Duration (B) Turn Error for both groups
Figure 2. Bar graphs demonstrating dierences between; A) group and hemispheric cSP duration, B) group
by stable turn variables: Turn Duration, Turn Error, and Turn Velocity
Figure 1. Quantication of TMS and cSP from a representative participant: A)TMS procedure conducted in a seated position separately to each cortical hemisphere. B) Filtered EMG trace of
muscle activity following TMS with wave descriptors. C) Filtered and rectied EMG trace of muscle activity with the horizontal solid line depicting the pre-stimulus mean and the dashed
horizontal lines depicting ± 2.2 SD’s of the pre-stimulus mean. Silent period is quantied as the time when the EMG trace dips below -2.2 SD’s and ends when the EMG trace exceeds the -2.2 SD
line for 5 consecutive data points.
Table 1. Table indicating the correlation between hemispheric cSP duration and
turning characteristics in healthy controls and PwMS
Regardless of cSP duration, healthy controls display greater
turning error. PwMS who have a shorter cSP demonstrate
reduced turning error while those with a greater cSP have
similar turning error to healthy controls.
PwMS who demonstrate a shorter cSP take longer to
complete a 360˚ turn, while healthy controls with a longer
cSP demonstrate longer turn durations. These results reveal
opposing trends with regard to cSP duration
Healthy
Control
PwMS
A B
Stable
Turns
A
Turn Velocity (˚/s)
PwMS
Control
50
150
200
400
350
300
250
100
Turn Error (˚)
PwMS
Control
10
20
30
25
15
5
Turn Duration (s)
PwMS
Control
1.0
2.0
3.0
2.5
1.5
0.5
Right Hemisphere
Left Hemisphere
30
60
90
150
120
Cortical Silent Period (ms)
*
*
*
Table 1
Left
Hemisphere
Right
Hemisphere
Control
PwMS
Control
PwMS
Pearson
Correlation
0.315
-0.481
0.159
0.030
Signicance
0.295
0.037
0.644
0.603
Pearson
Correlation
-0.150
0.489
0.184
0.158
Signicance
0.625
0.034
0.591
0.548
Pearson
Correlation
-0.278
0.449
-0.208
0.213
Signicance
0.357
0.054
0.526
0.495
Duration (s) Turning Error (˚) Velocity (˚/s)
-100
-50
0
50
100
150
200
250
300
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
I
I
III
II
TMS Stimulation
III
-100
-50
0
50
100
150
200
250
300
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
I
II
Time (ms) Time (ms)
EMG Amplitude (µV)
EMG Amplitude (mV)
TMS Stimulation
BC
A
15% MVC
Visual
Results
Background & Objectives
Turning is ubiquitous, with 20-50% of all steps measured to be
turns.1 Additionally, our ability to turn requires dynamic, whole
body coordination to achieve a change in direction. However,
turning becomes more dicult with the progression of diseases
such as multiple sclerosis.2
Increased levels of the inhibitory neurotransmitter
gamma-aminobutyric acid (GABA) within the motor cortex are
signicantly associated with coordination of the lower extremities
for older adults while walking.3
The objective of this project was to understand how motor cortex
inhibition contributes to the control of turning characteristics in
people with multiple sclerosis (PwMS) and healthy controls using
transcranial magnetic stimulation (TMS) and wireless inertial
sensors.
Data Analysis
- Turning metrics were automatically calculated using Mobility Lab software Version 2 (APDM, Portland, OR, USA)
- cSP duration was identied in regard to hemisphere stimulated
- For cSP, a 2x2 ANOVA was used to identify dierences between groups and hemispheres
- For the comparison between turning characteristics and groups, a pairwise comparison was completed for all three turning characteristics
- All data are presented as mean ± SD unless otherwise noted
The current results form this on-going study highlight the cortical inuence for dynamic movements. Although cSP
duration was not signicantly dierent between groups or hemispheres, signicant correlations were observed for
turning metrics and cSP duration for the left hemisphere in PwMS, such that greater motor cortex inhibition was
associated with better turning performance which resembled the healthy control cohort. These preliminary results
indicate that inhibition may be a crucial neural mechanism underlying dynamic movements that are strongly
associated with fall risk. However, additional testing is needed to make more denitive claims.
Conclusion References:
[1] Thigpen, M. T., Light, K. E., Creel, G. L., & Flynn, S. M. (2000). Turning
diculty characteristics of adults aged 65 years or older. Physical
Therapy, 80(12), 1174-1187.
[2] Spain, R. I., M. Mancini, F. B. Horak and D. Bourdette (2014). Body-worn
sensors capture variability, but not decline, of gait and balance measures
in multiple sclerosis over 18 months. Gait & Posture 39(3): 958-964
[3] Swanson, C. W. and B. W. Fling (2018). "Associations between gait
coordination, variability and motor cortex inhibition in young and older
adults." Experimental Gerontology 113
Support:
This work was supported by a David Mahoney Neuroimaging Grant from
The Dana Foundation.
Acknowledgments:
We would like to thank all of the individuals who volunteered their time
to participate in our study.
TMS Collection:
- Single pulse transcranial magnetic stimulation (TMS) was used to assess motor cortex inhibition via the cortical silent
period (cSP). The leg regions of the right and left motor cortices were determined by identifying the resting motor
threshold of the respective tibialis anterior muscles.
- To assess the cSP, participants were asked to maintain isometric ankle dorsiexion at 15% of their maximal voluntary
contraction for 2-minutes, during which time they received visual feedback.
- Concurrently, a TMS stimulation was given at 120% of resting motor threshold every 7-10 seconds for a minimum of twelve
cSPs.3 This procedure was conducted for both legs on every participant.
Turning Collection:
- Three stable turns, dened as a 360˚ to the right with an immediate 360˚ turn back to the left were collected and averaged.
- Turning characteristics assessed included: turn velocity (˚/s), duration (s), and turn error (˚) [achieved turn angle – expected].
- Participants wore ve wireless inertial sensors (APDM) placed on the forehead, sternum, lumbar (L5), and around each foot.
Methods & Design
Demographics
32 Participants have completed this on-going study:
- 19 PwMS: 5 Male | 14 Female; Age (y) [42.8 ± 17.7] ; EDSS
median 4.0 [range 0 - 4]
- 13 Healthy controls: 4 Male | 9 Female; Age (y) [49.7 ±
11.0]
Latency Period
II
III
Motor Evoked Potential
Cortical Silent Period
B
r = -0.15, p = 0.63
r = 0.49, p = 0.03
r = 0.32, p = 0.29
r = -0.48, p = 0.04
50 100 150 200
cSP Duration (ms)
-40
-20
0
20
40
60 cSP Duration vs. Turning Error
50 100 150 200
cSP Duration (ms)
1
1.5
2
2.5
3
3.5
4
Turn Duration (s)
cSP Duration vs. Turn Duration
Turning Error (˚)
0
0
A
Email: ClaytonSwanson@colostate.edu
Twitter: @Swanson_CW