The supplementary motor region and speech emission.

Speech disorders occur with left supplementary motor region (SMR) lesions. Right SMR lesions probably produce speech disorders only when the right cerebral hemisphere is speech-dominant. Paroxysmal SMR dysfunction produces both uncontrollable vocalization and speech arrest. Slowly evolving SMR lesions produce reduced and labored speech output with word-finding difficulties. Suddenly acquired SMR lesions produce marked speech suppression and aphonia; during recovery nonpropositional "automatic" speech may be initiated easily, even involuntarily, while initiation of propositional speech is still difficult or impossible. From the data one can infer that the SMR plays a role in "language" aspects of speech (in word finding, in a mechanism facilitating the emission of propositional over "automatic" speech), and also in the "motor" aspects of speech emission (including rhythm control and the control of phonation and articulation).