Speech rehabilitation in Parkinson’s Disease

Abstract

Parkinson’s disease (PD) is a chronic progressive neurodegenerative disorder with an increasing incidence worldwide. PD is characterized by the idiopathic loss of dopaminergic neurons, primarily in the anterior part of the substantia nigra [1].  The main symptoms of PD result from significantly reduced activity of dopaminergic neurons in the pars compacta region of the substantia nigra [2]. There are several pathways in the brain connecting other brain areas with the basal ganglia:  motor, oculmotor, associative,  limbic and  orbitofrontal pathways,  All these tracts  are affected in PD, and their dysfunction explains many of the symptoms of the disease since these pathways are involved in different functions including motor activities, attention and learning. The motor pathway has been examined more intensively than other tracts. The model of motor pathway alteration in PD has been studied extensively  for the last three decades,  although some aspects of the model and the hypothesis as a whole have been challenged which have led to various modifications.  According to this model, the basal ganglia normally inhibits a number of motor systems, preventing them from becoming inappropriately active. When a motivation or decision is made to perform an action, inhibitary influence is reduced for the target motor system, facilitating the activation. Dopamine has a major role in such inhibition, so high levels of dopamine can promote motor activity, whereas low levels of dopamine require greater effort for any given movement. This mechanism- dopamine depletion is the cause of  hypokinesia and reduced motor output.  Pharmacotherapy of PD is aimed to induce excessive dopamine activity, prevent the activation of motor systems at inappropriate times and thereby prevent dyskinesias.