The main disease associated with low brain dopamine is Parkinson's disease. In this degenerative condition, production in the 'substantia nigra of the brain stem' (the region of the brain in which it acts) decays rapidly, resulting in impaired communication of neurons responsible for motor system modulation.
One of the functions of dopamine is to control voluntary movements, thus its deficiency leads to the difficulty of movement characteristic of Parkinson, which is marked by stiffness and tremors.
A representative sample is a subset of a population that seeks to accurately reflect the characteristics of the larger group. For example, a classroom of 30 students with 15 males and 15 females could generate a representative sample that might include six students: three males and three females.
