Dissociation of sleep stages between the two hemispheres in a case with unilateral thalamic tumor.

A case with an astrocytoma in the right basal ganglia, suspected of having originated from the posterior ventro-lateral part of the thalamus, without any clinical findings indicating severe internal hydrocephalus and cortical damaged, showed dissociation of sleep stages between the two hemispheres, i.e., the affected side always fell earlier into deeper stages of sleep and was more difficult to arouse by sonic stimulations than the other side. It is assumed that this bilateral dissociation with ipsilateral deactivation is due to the severe unilateral reduction of EEG activating influences from the brain stem and a possible functional damage to the interthalamic commissures. This finding can be explained sufficiently by recent theories based on experimental results in animals. The clinical value of this findings is also discussed in this paper.