Postural responses to multidirectional stance perturbations in cerebellar ataxia

Area of Science:

• Neuroscience
• Biomechanics
• Human Motor Control

Background:

• Previous research linked cerebellar damage to balance deficits, primarily in the sagittal plane and focusing on leg muscles.
• The cerebellum's role in multi-directional postural control and intersegmental coordination remains less understood, especially in degenerative conditions like spinocerebellar ataxia (SCA).

Purpose of the Study:

• To investigate the impact of degenerative cerebellar lesions on multi-directional postural control in SCA patients.
• To determine if SCA-related instability is more pronounced in the sagittal or frontal planes.
• To explore whether instability arises from increased or decreased joint motion.

Main Methods:

• Nine patients with autosomal dominant spinocerebellar ataxia (SCA) and 12 controls underwent support surface rotations in eight directions.
• Full-body kinematics were used to analyze center of mass (COM) and body segment displacements.
• Surface electromyography (EMG) recorded activity from 10 leg, trunk, and arm muscles.

Main Results:

• SCA patients showed greatest instability with backward and lateral perturbations.
• Instability was linked to reduced knee flexion and excessive pelvic (roll) and trunk (pitch) motion.
• Muscle responses in SCA patients featured increased late balance-correcting activity.

Conclusions:

• Postural instability in SCA patients is significantly influenced by reduced knee flexion ('knee locking') and hypermetric trunk/pelvic movements.
• This specific pathophysiology in SCA differs notably from that observed in other patient populations with balance disorders.
• Findings suggest altered vestibulocerebellar control over leg muscles or compensatory strategies in SCA.