Mapping proprioceptive function using corticokinematic coherence in ataxias

Measurement and mapping of integrated activity across the length of motor and sensory systems (cortex to periphery) has value in a range of disorders from stroke to demyelination to traumatic injury. Examples include central motor conduction time using transcranial magnetic resonance imaging and somatosensory evoked responses. While clinical testing of conscious proprioception is part of the neurologic examination, objective testing of the proprioceptive pathways is challenging. Corticokinematic coherence (CKC) quantifies the coupling between oscillatory cortical activity, measured with EEG or magnetoencephalography (MEG), and limb kinematics (e.g., acceleration) during repetitive rhythmic voluntary or passive movements.^1,2 CKC peaks at hand movement frequency (F0) and its first harmonic (F1). Besides finger movement, toe and ankle movements can also be assessed. CKC primarily reflects proprioceptive processing in the primary sensorimotor area (SM1)³ with an apparent latency of 50 to 100 milliseconds. There seems to be adequate session-to-session reproducibility.¹ Movement rate has no effect on the coherence levels and the location of coherent sources.⁴ A stronger CKC at F1 in the dominant leg is noted in older compared with younger individuals and is associated with worse postural balance.⁵ Such a change may reflect inefficient and thus overcompensation of cortical processing of the proprioceptive afference or functional deficits in the peripheral proprioceptors and spinal circuits.⁵ The signal can be elicited even in neonates.⁶