Which statement regarding dopamine antagonists in Parkinson's disease is true?

Dopamine antagonists are primarily known for their role in decreasing dopaminergic activity in the brain. In the context of Parkinson's disease, which is characterized by a deficiency of dopamine due to the degeneration of dopaminergic neurons in the substantia nigra, the application of dopamine antagonists can lead to further reductions in dopamine levels, exacerbating motor function impairment.

While in certain cases, such as treating side effects of medications or conditions with excessive dopaminergic activity (like certain psychoses), dopamine antagonists can be beneficial, in Parkinson’s disease, the net effect is generally detrimental to motor function. Therefore, stating that they decrease motor functions is accurate, as the worsening of the already impaired motor capabilities in patients is a significant clinical concern associated with the use of these medications.

By contrast, the other statements do not align with the known effects of dopamine antagonists in the treatment of Parkinson's disease; enhancing memory functions and stabilizing mood typically involve dopaminergic activity rather than antagonism, and while there might be some increase in seizure risk with certain medications, this is not a primary or well-established effect of dopamine antagonists themselves in the context of Parkinson's disease.