What I found interesting in my research so far is that there is a common pattern of problems with:
- executive function,
- motivation (a lack of which is called a lot of things, including ‘apathy’), and
- initiation of movement (including slowness and getting stuck).
These three areas of impairment (call it ‘Buckle’s triad of initiation impairments’ ;)) are commonly seen to varying degrees in:
Because one of the causes of this triad is quite well understood, i.e. deficiencies or damage to the basal ganglia in Parkinson’s, these regions could be important in other conditions that share those characteristics.
Each of these conditions suffers from the bias of medical practitioners and researchers who only see the most prominent, interesting or ‘abnormal’ features of the condition. So in Parkinson’s, they tend to see the movement disorder and overlook the apathy and other psychological symptoms. With depression, by contrast, the mood symptoms are most prominent and the psychomotor slowing that some with severe depression experience is seldom thought about.
In schizophrenia they are clearly most interested in the hallucinations and delusions, whereas in autism research focuses almost exclusively on the social and communication impairments. Yet in both of these, difficulty and differences in motor control, motivation and sensory processing are common or even universal aspects of the conditions.
These three aspects occur together and blend together so much that it can be very difficult to know where to draw the line between them. Also common with all of them are anxiety and difficulty making choices.