[Late EEG sequelae following psychosurgical interventions]. 
The tardive EEG-features resulting from psychosurgery are more prominent than commonly admitted.  The different types of surgical interventions, the localized scar-formation and the secondary degenerative lesions at a distance, mainly in the thalamic nuclei, resulting from disruption of corticothalamic connections following decortication, may lead to variable EEG-patterns.  The pathology underlying the tardive EEG-features may be complex and progressive for many years.  In the author's experience the most prominent EEG-features consist in localized beta-waves, sleep-spindles-asymmetry with spindles-activation at the undercut cortical regions and the development of a slow-wave focus in synchronized sleep-stages.  The pathophysiology of these EEG-characteristics is discussed in accordance with the clinical and experimental data available.  The value of activation procedures, with special reference to sleep, and the importance of psychotropic drugs for the development and interpretation of EEG-features following psychosurgery is particularly stressed.