Preparatory cortical and spinal settings to counteract anticipated and non-anticipated perturbations

Abstract

Abstract-Little is known about how the central nervous system prepares postural responses differently in anticipated compared to non-anticipated perturbations. To investigate this, participants were exposed to translational and rotational perturbations presented in a blocked (anticipated) and a random (non-anticipated) design. The preparatory setting ('central set') was measured by H-reflexes, motor-evoked potentials (MEPs), and short-interval intracortical inhibition (SICI) shortly before perturbation onset in the soleus of 15 healthy adults. Additionally, the behavioral consequences of differential preparatory settings were analyzed by comparing the short-(SLR), medium-(MLR), and longlatency response (LLR) of the soleus after anticipated and non-anticipated rotations and translations. H-reflexes elicited before perturbation were different between conditions (p = 0.023) with larger amplitudes in anticipated translations compared to anticipated rotations (37.0%; p = 0.048). Reduced SICI was found in the three conditions containing perturbations compared to static standing (p < 0.001). Muscular responses assessed after perturbations remained unchanged for the SLR and MLR, whereas the LLR was decreased in anticipated rotations (À36.2%; p = 0.002) and increased in anticipated translations (16.7%; p = 0.046) compared to the corresponding non-anticipated perturbation. As the SLR and MLR are organized at the spinal and the LLR at the cortical level, the preparatory setting seems to mainly influence cortically mediated postural responses. However, the modulation of the H-reflex before anticipated perturbations indicates that supraspinal centers adjusted Ia-afferent transmission for the soleus in a perturbationspecific manner. Intracortical inhibition was also modulated but differentiates to a lesser extent only between perturbation conditions and unperturbed stance.

Associations Between Types of Balance Performance in Healthy Individuals Across the Lifespan: A Systematic Review and Meta-Analysis

“…On the contrary, feedback control is characterized by the initiation of sufficient muscle responses after balance loss to compensate an unpredicted postural disturbance during one-legged standing and to avoid falling. In this respect, recent studies (Wälchli et al, 2017 ; Fujio et al, 2018 ) showed that the central nervous system differently prepares postural responses in expected compared to unexpected stance perturbations. For instance, Fujio et al ( 2018 ) examined motor-evoked potential (MEP) induced by transcranial magnetic stimulation during expected (via acoustic signal) and unexpected (no signal) perturbations, while standing on a moveable platform in healthy young adults (mean age: 27 ± 2 years).…”

Freely chosen cadence during cycling attenuates intracortical inhibition and increases intracortical facilitation compared to a similar fixed cadence

“…Short interval intracortical inhibition (SICI) was measured by applying two TMS pulses with an interstimulus interval of 2.5 ms (Wälchli et al, 2017;Lauber et al, 2018) where the first conditioning pulse was subthreshold (0.7 AMT) and the second test pulse was suprathreshold (1.2 AMT). The conditioning pulse activates intracortical inhibitory interneurons and attenuates the MEP evoked by the second pulse which reflect excitability of the corticospinal neurons (Di Lazzaro & Rothwell, 2014).…”

Forecast or Fall: Prediction's Importance to Postural Control

“…Since the seminal findings of Horak et al ( 29 ), researchers have used more direct measures of corticospinal excitability and spinal reflex modulation to reveal the preparatory activity that occurs in spinal and cortical networks in advance of a predictable perturbation ( 33 ). Several electroencephalography studies have shown that prior to a predictable postural disturbance, a slow wave potential builds under central scalp electrodes ( 34 – 36 ).…”

“…More recent studies have shown that this anticipatory cortical activity is similar regardless of whether the disturbance is self or externally induced ( 37 ) and it scales with the amplitude of the impending perturbation ( 32 ). Concurrent changes in the circuitry of the spinal cord accompany these anticipatory cortical potentials ( 33 ) implying that the purpose of this cortical activity may be to modify the “central set” or state of the nervous system ( 35 ), however, a causal relationship between the two remains to be defined.…”

“…Although control of postural equilibrium was long thought to be mediated subcortically ( 85 , 86 ), a large body of evidence now attests to the involvement of the cerebral cortex in the control of postural equilibrium, including compensatory reactions to unexpected postural challenge ( 32 , 33 , 87 , 88 ). Perhaps most crucial are compensatory reactions that require the limbs to establish a new base of support and catch a falling center of mass ( 89 – 91 ).…”