Dopamine and glutamate in motor and cognitive symptoms of parkinson's disease

Abstract

Parkinson's disease (PD) is characterized by motor and cognitive deficits. The main motor symptoms of PD are on the one hand hypokinetic signs, such as bradykinesia, akinesia, rigidity, and loss of postural reflexes, and on the other hand hyperkinetic signs, such as tremor, (see Chapter 21; ref. 1). Cognitive deficits in nondemented PD patients comprise deficits in sensitivity to reward (2), deficits in procedural and habit learning (3), and deficits in switching arbitrarily from one behavioral activity to another, possibly owing to a deficit in attentional set shifting (4). It has even been argued that PD patients are deficient in so-called executive functions of human mind (5,6). Executive function is a neuropsychological construct that has been used to capture the highest order of cognitive abilities, e.g., flexibility of thought in the generation of solutions to novel problems (7,8). The reason why the cognitive aspects are not well perceived may be that in humans, the cognitive functions in PD are mainly unconscious; they are thus not experienced and cannot be explicitely communicated. Another reason that renders analysis of PD symptoms so difficult is that the diseased human brain is able to use (cortical) loops to bypass or compensate for basal ganglia (BG) dysfunctions, however, with the disadvantage of a loss of parallel processing and reduced velocity. © 2005 Humana Press.