EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II 1

Effect of Arm Dominance on Long-Latency Stabilizing Reflex Gain during Posture

Elise H. E. WalkerEric J. Perreault

Northwestern University &Rehabilitation Institute of Chicago

EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II 2

Arm dominance as control specialization in the cortical hemispheres

__DOMINANT__ • Predictive

• Trajectory

• Limb dynamics

• Reach initiation

NONDOMINANT• Impedance

• Position

• Stabilizing

• Final position

Bagesteiro & Sainburg, J Neurophys 2002“Handedness: dominant arm advantages in control of limb dynamics”

Bagesteiro & Sainburg, J Neurophys 2003“Nondominant arm advantages in load compensation during rapid elbow joint movements”

Mani, Mutha, Przybyla, Haaland, Good, Sainburg, Brain 2013“Contralesional motor deficits after unilateral stroke reflect hemiphere-specific control mechanisms”

?

EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II 3

Modified from Shemmell et al. 2009 J Neurosci 29(42)

Time (ms)PTB

0.1 mV

-50 0 50 100 150

Bice

ps E

MG

Stiff DNICompliant DNI

Stabilizing stretch reflexes: task-appropriate feedback responses during posture

Hypothesis: Nondominant arm will display more effective stabilizing

stretch reflex

LLR

EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II 4

Postural experiment in right-handed subjects

• Dominant (R) & nondominant (L) arm

• Stable & unstable environments• Elbow flexor & extensor

perturbations

EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II 5

Perturbations of elbow posture elicit reflexes

EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II 6

Perturbations of elbow posture elicit reflexes

Onset ofPerturbation

EMG trace

BackgroundActivity

BGA

Short Latency

Early LongLatency

Late LongLatency

SLR LLR1 LLR2

10%MVC

0 50 10025 75-100 milliseconds

No change

↑ sensitivity forunstable, nondominant

EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II 7

Biceps

Some individual subjects display differences between arms

Brachioradialis

Feedforward mechanism

-50 ms 0 50 10025 75

R (dominant)L (nondominant)

25%MVC

Feedback mechanism

EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II 8

Unmatched reflexes were slightly higher in some left-arm muscles

Tric

eps L

ater

alTr

icep

s Lon

g

LLLL RRRR

*** ***

**

* *

..

LL LL RR RR

*** ***

****

** **

**

.*

**

.

BGA SLR LLR1 LLR2

10%MVC

BGA SLR LLR1 LLR2

10%MVC

EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II 9

Matched reflexes show no difference in sensitivity for the two arms

* *

* *

Tric

eps L

ater

al

L RL RL RL R

BGA SLR LLR1 LLR2

10%MVC

L RL R

Tric

eps L

ong

L RL R

BGA SLR LLR1 LLR2

10%MVC

Arm dominance does not influence reflex sensitivity

EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II 10

Arm dominance affects feedforward strategy, but does not affect feedback gains

• Stabilizing reflexes in the nondominant arm do not display greater sensitivity.

• Differences in reflex amplitude stem from feedforward strategies of muscle activation.

• Our current understanding of postural reflexes in the upper limb is probably not affected by arm dominance.

EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II 11

ACKNOWLEDGEMENTS

Support & Funding:

Northwestern

NSF 0932263

SMPP

Guidance:

Eric Perreault

Robert Sainburg

NMCL:Timothy Haswell

Daniel Ludvig

Claire Honeycutt

David Lipps

Hyunglae Lee

Rosalind Heckman

Emma Bailllargeon

John Spanias

Mariah Whitmore

Bing Wang

Andrea Beer

EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II 12

EMBC 2014, Chicago IL USA | Thursday, August 28 | Motor Learning and Neural Control II

Arm strength and task difficulty not significantly different between arms

A1