MESIAL CEREBRAL INCISION.

Abstract

LINICAL observations relate lesions of the brain stem to alterations in awareness. When the lesion extends into the third ventricle, it may be associated with amnestic confusion and confabulation, 24 or a peculiar state called akinetic mutism. 5 Pontine hemorrhages ~2 and hemorrhages in the posterior fossa la have been clearly correlated with profotmd (but sometimes reversible) alterations in awareness. From such clinical observations, Jefferson summarized the areas of the human brain in which lesions may produce stupor. As shown in Fig. 1, these areas are mesial or paramesial and related to the brain stem as defined by Herrick. TM According to Jefferson's interpretation, the relevant clinical phenomena depend on different degrees of de-afferentation at different levels. This is essentially the same view as Magoun presented in discussion of Cairns' celebrated case of akinetic mutism. He surmised tha t the epidermoid cyst interfered with reticular influences directed cephalically as well as caudally. 15 Both interpretations are, of course, based on the extensive and expanding body of experimental data which associates arousal with the ascending reticular act ivat ing system. Originally, Moruzzi and Magoun ~6 reported tha t the process of arousal depended on an excitation of the central brain stem and then elaborated the responsible mechanisms. Lindsley et al. ~4 demonstra ted tha t a cat whose classical sensory afferents were sectioned bilaterally, in mesencephalic tegmentum, was wakeful and had a normal electrogram. Whereas bilateral section (at the same level) which spared the classical