In the wake of the success of the dopamine hypothesis of schizophrenia, speculative hypotheses failing to proffer empirical support received little attention in research.
After a lengthy review of the evidence for and against the dopamine hypothesis, one psychiatrist proposed that antipsychotics primarily work not by modifying dopamine but instead by inducing neurocognitive suppression, which diminishes the severity of psychotic symptoms (Moncrieff, 2009).
Historical development of the dopamine hypothesis of schizophrenia.
The purpose of the present study was to investigate this dopamine hypothesis by observing the effects of a dopamine agonist on indices of motor performance and reinforcement efficacy derived from a matching law analysis of the relationship between response and reinforcement rates in a context where responding was reinforced by the opportunity to run.
This result would be consistent with Lambert's (1992) dopamine hypothesis. Alternatively, if k changes while Re remains unchanged, then the matching law analysis would suggest that amphetamine alters motoric rather than motivational aspects of reinforced responding and this result would not support Lambert's (1992) hypothesis.
Therefore, the results from the present study, although not negating the opiate hypothesis, lend support to the alternative dopamine hypothesis. Further support for the dopamine hypothesis may come with future investigation of the effects of selective dopamine antagonists on responding reinforced by the opportunity to run.