Limbic Ictus and Atypical Psychoses

Abstract

This paper reviews the data which support the concept of a limbic ictus as an etiological mechanism in many patients with diagnoses of atypical psychoses. Inasmuch as our clinical neurophysiological techniques cannot easily record this limbic ictus, much of these data are circumstantial. Furthermore, lacking reliable biological markers for the major psychoses, supporting animal data rests on the tenuous identification of psychoses in terms of behavioral observation on these animals, whereas our psychiatric diagnostic criteria for psychoses depend largely on the verbal reports of our patients. There is, however, direct empirical support for this concept which is limited to a small cohort whose psychoses were correlated with electrographic data recorded from chronically implanted subcortical electrodes. These data include not only observations of spontaneously appearing ictal or interictal patterns but also observations following electrical stimulation of subcortical structures. The kindling phenomena induced by such electrical stimulation in animals have also been observed in humans. Kindling then offers a theoretical framework within which to view more prolonged behavioral deviations as neurophysiological processes, although it is still not completely clear whether such deviations are correlated with ictal or interictal phenomena. Some drugs such as cocaine and amphetamine reduce seizural thresholds within the limbic system, and hence facilitate kindling. In fact, some of the neuroleptics and tricyclics now utilized in the treatment of not only the major psychoses but also the atypical psychoses also lower seizural thresholds. This may explain why such drugs often exaggerate rather than ameliorate the symptoms of atypical psychoses. Furthermore, this means that drugs which raise seizural thresholds could be an important addition to our therapeutic armamentarium. This has been particularly demonstrated by the use of the anticonvulsant carbamazepine. Animal studies have shown that this drug is particularly effective in blocking the kindling phenomena in the amygdala. It is still not clear whether the therapeutic effectiveness of carbamazepine in treating the atypical psychoses is due to its anticonvulsant properties or some other action on synaptic neurotransmission with the elevation in seizural threshold as an incidental consequence with regard to the drug's effectiveness in the atypical psychoses.