Speech disturbances following stereotaxic surgery in ventrolateral thalamus.

Patients operated on stereotactically in the ventrolateral thalamic structures show after stimulation or following the operation some disturbances which apparently interfere with cerebral speech mechanisms, i.e. speech arrest, word iterations or recurring utterances, lack of initiative to speak, hypoprosodia, change of the speed of enunciation. These phenomena rather concern motor processes, the initiation of speech, the maintenance and control of speech, fluency and volume. They may occur after lesions or stimulations in any of both hemispheres, however, there is a clear preponderance after lesions or stimulations on the left side. Dysphasic disturbances were observed only as transient phenomena. One can conclude that in this case thalamotomy influences the function of the dominant cortical regions for language rather than subcortical structures concerned with speech function. Differences in verbally expressed cognition between subjects with left-sided and right-sided ventrolateral thalamotomy can be observed, not only in the immediate post-operative period, but also after a much longer interval.