corticospinal pathways to control balance Stphane Baudry - PowerPoint PPT Presentation

Laboratory of Applied Biology ULB Neuroscience Institute Université Libre de Bruxelles Aging changes the contribution of spinal and corticospinal pathways to control balance Stéphane Baudry

Gravity-driven instability of upright posture Abrahamova and Hlavacka, 2008

Neuromuscular components of upright standing: reflex standing? Decerebrate cat Brainstem transection (Sherrington 1910) CoM CoM

Neuromuscular components of upright standing: reflex standing? Decerebrate cat Brainstem transection (Sherrington 1910) Afferent Spinal network information Muscle activation Maintaining upright standing

Neuromuscular components of upright standing: supraspinal component? Ultrasound image Loram et al. 2004

Neuromuscular components of upright standing Defining Sensorimotor “Postural set” integration Supraspinal structures Afferent Spinal network information Muscle activation Maintaining upright standing

Spinal and corticospinal inputs onto soleus motoneurons Corticospinal pathway Soleus motor Muscle spindles neurons pathway Muscle activation Maintaining upright standing

Muscle spindles pathway Motoneurons Presynaptic terminals Motor axons Group Ia afferents (from muscle spindles) Hoffmann (H) reflex

Muscle spindles pathway M wave H reflex 2 mV 5 ms Intensity

Influence of age on H reflex during upright standing n = 142 Baudry 2016

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?  Ia Presynaptic inhibition PADs Ia afferents MNs Baudry and Duchateau 2012

Greater decrease in H reflex from seated to standing in older n=40 Baudry et al. 2015

Reduced synaptic inputs from group I afferents with age - Muscle spindles Soleus motor afferent inputs neuron pool -

Increased feedback latency Young Middle-aged Older H reflex Latency  Increase in time-delayed feedback  Reduction in synchronisation of synaptic inputs Scaglioni et al. 2003

Decreased reflex mechanical output Young Older  Torque output  Rate of torque development Scaglioni et al. 2003

Decreased relevance of muscle spindles afferents in upright standing - Muscle spindles Soleus motor afferent inputs neuron pool  Mechanical output  latency

Corticospinal pathway Transcranial magnetic stimulation - TMS + Corticospinal cells TMS + - + Cortico-cortical cells Spinal cord + Interneurones + - + Motorneurones MEP

Corticospinal pathway Transcranial magnetic stimulation - TMS MEP

Influence of age on H reflex during upright standing n = 94 Baudry 2016

Influence of age on MEP during upright standing Baudry 2016

Increased contribution of corticospinal inputs - Corticospinal Muscle spindles Soleus motor + afferent inputs inputs neuron pool  Mechanical output  latency

Increased in plantar flexor activity during upright standing Billot et al. 2010 Vandervoort and McComas, 1986

Increased in muscle activation aEMG (% MVC) Baudry et al. 2012 Billot et al. 2010

Increased corticomotoneuronal excitability Corticospinal cells MN Interneuron Corticomotoneuronal pathway MEP

Increased corticomotoneuronal excitability Baudry et al. 2014 MEP

Influence of muscle activation of H reflex  Increase in muscle activity may alter proprioceptive signal Proske and Gandevia 2012 n = 94 Baudry 2016

Increase in muscle activation is associated with increased corticomotoneuronal drive and reduced relevance of group I afferents  Muscle activity  force - - Muscle spindles Corticospinal Soleus motor + + afferent inputs inputs neuron pool  Mechanical output  latency

Increased coactivation Coactivation index (%) Nagai et al. 2011 Coactivation index: EMG-TA/EMG-SOL  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

Ageing changes the contribution of spinal and corticospinal pathway to control balance  coactivation  Muscle activity  force - - Corticospinal Muscle spindles Soleus motor + + afferent inputs inputs neuron pool  Mechanical output  latency

Training can modify age-related changes Penzer et al. 2015

Ageing changes the contribution of spinal and corticospinal pathway to control balance  coactivation  Muscle activity  force - - Corticospinal Muscle spindles Soleus motor + + afferent inputs inputs neuron pool  Mechanical output  Those changes can likely be minimized by training  latency