aging changes the contribution of spinal and corticospinal ... fileaging changes the contribution of...
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Aging changes the contribution of spinal and corticospinal pathways to control balance
Stéphane Baudry
Laboratory of Applied BiologyULB Neuroscience InstituteUniversité Libre de Bruxelles
Gravity-driven instability of upright posture
Abrahamova and Hlavacka, 2008
Neuromuscular components of upright standing: reflex standing?
Decerebrate catBrainstem transection(Sherrington 1910)
CoM CoM
Neuromuscular components of upright standing: reflex standing?
Afferent information
Muscle activation
Maintainingupright standing
Spinal network
Decerebrate catBrainstem transection(Sherrington 1910)
Neuromuscular components of upright standing: supraspinal component?
Ultrasound image
Loram et al. 2004
Neuromuscular components of upright standing
Afferent information
Muscle activation
Maintainingupright standing
Defining “Postural set”
Sensorimotor integration
Spinal network
Supraspinal structures
Spinal and corticospinal inputs onto soleus motoneurons
Muscle spindles pathway
Muscle activation
Maintainingupright standing
Corticospinal pathway
Soleus motor neurons
Muscle spindles pathway
Group Ia afferents(from muscle spindles)
Motor axons
MotoneuronsPresynaptic terminals
Hoffmann (H) reflex
Muscle spindles pathway
M wave H reflex
5 ms
2 mV
Intensity
Influence of age on H reflex during upright standing
Baudry 2016
n = 142
Reflex gain
Klass et al. 2011
Presynaptic origin for the greater H-reflex modulation in older?
Baudry and Duchateau 2012
Presynaptic origin for the greater H-reflex modulation in older?
Baudry and Duchateau 2012
Presynaptic origin for the greater H-reflex modulation in older?
Baudry and Duchateau 2012
PADs
MNsIa afferents
Ia Presynaptic inhibition
Greater decrease in H reflex from seated to standing in older
Baudry et al. 2015n=40
Reduced synaptic inputs from group I afferents with age
Soleus motorneuron pool
--Muscle spindles
afferent inputs
Increased feedback latency
H reflex
Latency
Young Middle-aged Older
Increase in time-delayed feedback
Reduction in synchronisation of synaptic inputsScaglioni et al. 2003
Decreased reflex mechanical output
Scaglioni et al. 2003
Torque output Rate of torque development
Young Older
Decreased relevance of muscle spindles afferents in upright standing
Muscle spindlesafferent inputs
Soleus motorneuron pool-
latency
Mechanicaloutput
MEP
Corticospinal pathway
TMS Corticospinal cells
Cortico-cortical cells
Interneurones
Motorneurones
+
+ +-
+
++-
Spinal cord
Transcranial magneticstimulation - TMS
MEP
Corticospinal pathwayTranscranial magneticstimulation - TMS
Influence of age on H reflex during upright standing
Baudry 2016
n = 94
Influence of age on MEP during upright standing
Baudry 2016
Increased contribution of corticospinal inputs
Corticospinalinputs
Soleus motorneuron pool- +
latency
Mechanicaloutput
Muscle spindlesafferent inputs
Increased in plantar flexor activity during upright standing
Vandervoort and McComas, 1986 Billot et al. 2010
Increased in muscle activation
Baudry et al. 2012 Billot et al. 2010
aEM
G(%
MV
C)
Increased corticomotoneuronal excitability
MEP
MN
Interneuron
Corticospinal cells
Corticomotoneuronalpathway
Increased corticomotoneuronal excitability
MEP Baudry et al. 2014
Influence of muscle activation of H reflex
Baudry 2016
Increase in muscle activity mayalter proprioceptive signalProske and Gandevia 2012
n = 94
Increase in muscle activation is associated with increased corticomotoneuronal drive and reduced relevance of group I afferents
Corticospinalinputs
Soleus motorneuron pool- +
latency
Mechanicaloutput
- +
Muscle activity
force
Muscle spindlesafferent inputs
Increased coactivation
combining high reflex gain (large H-reflex amplitude) and coactivation has an undesired effect on the steadiness of the motor output Dideriksen et al. 2015
Greater coactivation in older adults likely reduces the relevance of muscle afferent inputs
Coactivation index: EMG-TA/EMG-SOLNagai et al. 2011
Co
acti
vati
on
ind
ex (
%)
Ageing changes the contribution of spinal and corticospinal pathway to control balance
Corticospinalinputs
Soleus motorneuron pool- +
latency
Mechanicaloutput
- +
coactivation
Muscle activity
force
Muscle spindlesafferent inputs
Training can modify age-related changes
Penzer et al. 2015
Ageing changes the contribution of spinal and corticospinal pathway to control balance
Corticospinalinputs
Soleus motorneuron pool- +
latency
Mechanicaloutput
- +
coactivation
Muscle activity
force
Muscle spindlesafferent inputs
Those changes can likely be minimized by training