Neural mechanisms of single corrective steps evoked in the standing rabbit

Abstract

Single steps in different directions are often used for postural corrections. However, our knowledge about the neural mechanisms underlying their generation is scarce. This study was aimed to characterize the corrective steps generated in response to disturbances of the basic body configuration caused by forward, backward or outward displacement of the hindlimb, as well as to reveal location in the CNS of the corrective step generating mechanisms. Video recording of the motor response to translation of the supporting surface under the hindlimb along with contact forces and activity of back and limb muscles was performed in freely standing intact and in fixed postmammillary rabbits. In intact rabbits, displacement of the hindlimb in any direction caused a lateral trunk movement towards the contralateral hindlimb, and then a corrective step in the direction opposite to the initial displacement. The time difference between onsets of these two events varied considerably. The EMG pattern in the supporting hindlimb was similar for all directions of corrective steps. It caused the increase in the limb stiffness. EMG pattern in the stepping limb differed in steps with different directions. In postmammillary rabbits the corrective stepping movements, as well as EMG patterns in both stepping and standing hindlimbs were similar to those observed in intact rabbits. This study demonstrates that the corrective trunk and limb movements are generated by separate mechanisms activated by sensory signals from the deviated limb. The neuronal networks generating postural corrective steps reside in the brainstem, cerebellum, and spinal cord.

Balance Control Mediated by Vestibular Circuits Directing Limb Extension or Antagonist Muscle Co-activation

“…Recently, subpopulations of vestibular nuclei neurons in the cat have been shown to alter their firing in response to extension, flexion, or unidirectional movements of the hindlimb (McCall et al, 2016). Given the importance of somatosensory information for postural control (Karayannidou et al, 2009;Hsu et al, 2017), it seems likely that the LVN serves to integrate multiple modalities of sensory information concerning body and limb position and movement, with activation of a select set of these inputs recruiting a subpopulation of LVN neurons to appropriately modify spinal motor programs.…”

Associating white matter microstructural integrity and improvements in reactive stepping in people with Parkinson’s Disease

“…Reactive balance responses are composed of three phases mediated by a distributed and complex neural network: 1) short-latency (SL) < 80 ms, 2) medium-latency (ML) 80-120 ms, and 3) long-latency (LL) > 120 ms (Jacobs & Horak, 2007). The earliest phases of the responses involve spinal (Fung & Macpherson, 1999; Macpherson et al, 1997) and subcortical structures (Honeycutt & Nichols, 2010;Hsu et al, 2017;Stapley & Drew, 2009), with cortical regions exerting more signi cant in uence as the balance responses progress (Adkin et al, 2006;Dietz et al, 1985;Dimitrov et al, 1996;Ghosn et al, 2020;Marlin et al, 2014;Palmer et al, 2021; Payne & Ting, 2020). Although little work has assessed the neural underpinnings of reactive balance in PwPD, a recent connectivity study associated the subcortical and cerebellar networks with reactive balance in PwPD (Ragothaman et al, 2022).…”

Activity of Spinal Interneurons during Forward and Backward Locomotion

“…Backward and sideways locomotion are usually generated in the context of avoidance behavior. In addition, single steps in different directions are generated for postural corrections to restore balance or the basic body configuration perturbed during standing (Beloozerova et al, 2003;Karayannidou et al, 2009;Hsu et al, 2017) and FW locomotion (Musienko et al, 2014).…”

“…The latter includes networks generating the horizontal component of the step in different directions. It was also suggested that the same mechanisms generate a single corrective step in a particular direction in response to sensory information signaling a distortion of balance or body configuration (Hsu et al, 2017).…”