Bradykinesia represents one of the cardinal and most incapacitating features of Parkinson’s disease (PD). In this context,
investigating the cerebral control mechanisms for limb movements and defining the associated functional neuroanatomy is important
for understanding the impaired motor activity in PD. So far, most studies have focused on motor control of upper limb movements
in PD. Ankle movement functional MRI (fMRI) paradigms have been used to non-invasively investigate supraspinal control mechanisms
relevant for lower limb movements in healthy subjects, patients with Multiple sclerosis, and stroke. Using such an active
and passive paradigm in 20 PD patients off medication (mean age 66.8 ± 7.2 years) and 20 healthy controls (HC; mean age 62.3 ± 6.9 years),
we here wished to probe for possible activation differences between PD and HC and define functional correlates of lower limb
function in PD. Active ankle movement versus rest was associated with a robust activation pattern in expected somatotopy involving
key motor areas both in PD and HC. However, contrasting activation patterns in patients versus controls revealed excess activation
in the patients in frontal regions comprising pre-supplementary motor areas (pre-SMA) and SMA proper. The extent of SMA activation
did not correlate with behavioural parameters related to gait or motor function, and no differences were seen with the passive
paradigm. This finding might be indicative of higher demand and increased effort in PD patients to ensure adequate motor function
despite existing deficits. The missing correlation with behavioural variables and lack of differences with the passive paradigm
suggests that this excess activation is not exclusively compensatory and also not hard-wired.
Keywords Gait dysfunction – Parkinson’s disease – fMRI – SMA proper – Pre-SMA
P. Katschnig, P. Schwingenschuh contributed equally to this work.