My perception of the progress of Parkinson’s disease is that I am gradually losing control of my body. Is this justified? What control do I have? What does it mean to lose this control?
Heidegger argued that we only know the truth of objects by interacting with them. For example, a description of what a hammer does is incomplete without actually holding a hammer and using it. In other words, we are the essential mediators of truth. Heidegger saw there are two types of object, those we can interact with and truly know (called ready-at-hand) and those beyond our reach (called present-at-hand).
For instance, I am interacting in a specific way with the computer in front of me to type these words and as such the computer is ready-at-hand for me. This is possible because the computer is designed to be useable within the limits of my thrownness (the state in which I exist); for example, the screen produces light in the visual spectrum and the keys are designed to be pressed down using the strength of the muscles and tendons in my hands and arms. Indeed, all things designed for human use must fall within the boundary of our thrownness if they are to be useful.
Natural (non-man made) objects can also be ready-at-hand, in that they are exploitable within our thrownness. It is wrong to assume such objects were designed to be this way. If our thrownness happened to be different then the range of objects that are ready-at-hand for us would also be different. It could be argued that our success as a species is down to the wide range of objects that are ready-at-hand for us.
However, there are many objects that we cannot interact with; these are merely present-at-hand. For example, although we can see light reflected from the surface of Mars (only the light is ready-at-hand), we cannot interact with or truly know the objects on the surface of Mars; they remain present-at-hand until we experience them directly.
Our thrownness includes the ability to control our body through its interaction with our conscious will, thereby making specific movements of the body ready-at-hand (e.g. moving the many muscles and tendons required to type these words). However, most of the processes of the body are devoid of direct conscious interaction and therefore are present-at-hand. Nonetheless, consciousness can indirectly influence some of these processes; for example, heart rate is controlled unconsciously but going for a run increases heart rate.
Parkinson’s interferes with the interaction between consciousness and the body; therefore, the progressive loss of control in Parkinson’s could be seen as a shift from the body being ready-at-hand to becoming increasingly present-at-hand.
If interaction is key to knowing, it follows that as the interaction is curtailed in Parkinson’s the possibility of knowing the control and movement we had before is also curtailed. But the mind interacts with itself and Parkinson’s interferes much less with this relationship; therefore, as control of the body is lost the mind continues to know itself and retains the ability to indirectly influence the symptoms of Parkinson’s.