Movement disorders: In Parkinson's disease, the inhibition of the cortical spinal cord gradually disappears

Parkinson's disease (PD) is characterized by pathological neurodegeneration of the substantia nigra, leading to dopamine depletion of the striatum and dysfunction
of the cortico-basal ganglion circuit.

Figure 1: Cover art of the paper

Here, we propose that this motor retardation may be associated
with dynamic changes in corticospinal excitability that support autonomous motor readiness.

Previous TMS studies of PD have found abnormal changes within the locomotor system, including a weakening of M1 inhibition levels, accompanied by an increase
in corticospinal cord output.

With this, Wilhelm et al.

To address these predictions, in PD patients and healthy control groups (HCs), we applied TMS on M1 during the indicated delayed selection RT task, testing twice on different days; Patients are tested
when they are not using or using dopamine replacement therapy (DRT).

For two consecutive days, 29 PD patients (taking and not taking medication) and 29 matched healthy control groups (HCs) received transcranial magnetic stimulation that caused motor evoked potentials (MEPs) in the target hand muscles, while they were either at rest or prepared for left- or right-handed reactions during the indicator-delay selection reaction
time task.

Figure 2: Graph of the paper results

In contrast to HCs, PD patients exhibit a lack of preparedness inhibition when analyzing the side of the responding hand, especially when the latter is the most severely affected side
.

This deficiency does not depend on dopamine drug therapy, it increases with the course of the disease and is associated
with the movement disorders measured by Part III (Total Score and Movement Retardation Score) of the Association for Movement Disorders Unified Parkinson's Disease Rating Scale.

Readiness inhibition gradually disappears in Parkinson's disease, synchronized with the exacerbation of motor symptoms, including bradykinesia
.

Original source:

Wilhelm E, Quoilin C, Derosiere G, Paço S, Jeanjean A, Duque J.