Question
What is the hallmark feature of cognitive dysfunction in clients with Parkinson's Disease without dementia?
Answer
Executive dysfunction is considered the hallmark feature of cognitive impairment in Parkinson's disease. Executive dysfunction means impairment in the cognitive processes that are involved in planning, carrying out, and regulating complex goal-directed behavior. Executive functions are particularly important when habitual responses or thought processes cannot be used or need to be suppressed. Executive functions are particularly important for novel situations or context where you cannot rely on habits, procedural memory or even stored knowledge in memory. Executive functions can also be thought of as higher order cognitive processes that control lower order cognitive functions like memory and sensory perceptual functions. Your executive functions allow you to organize and coordinate the information stored and/or generated by those lower level functions, and then use them in an efficient way. Executive functions orchestrate many of our daily occupations particularly more complex activities like instrumental ADLs, social interactions, and leisure pursuits. These are things that tend to be different every time you do them. Although you need your whole brain for executive functioning, executive functioning is thought to be mediated primarily by the prefrontal cortex.
If the primary brain region affected by Parkinson's disease is the basal ganglia, why are these prefrontal mediated functions impaired? This is because of corticobasal ganglia thalamocortical loops, or the frontostriatal circuitry. What happens is the basal ganglia receive input from most of the cerebral cortex and then the basal ganglia, in turn, project back out to many frontal lobe regions by the thalamus. The primary cause of the cognitive impairment that is observed in early non-demented Parkinson's disease is thought to be dysfunction in these frontostriatal circuits due to dopamine depletion in the basal ganglia and also in the prefrontal cortex. The degeneration of the dopamine neurons in the basal ganglia affects cognitive functioning through its connections with these important prefrontal cortical regions.
