Role of Hypothalamic Mechanisms in Thalamic Pain

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Abstract
For the development of thalamic pain, ascending impulses entering the diencephalon are essential, since the thalamic pain dissapears if the ascending systems passing through the midbrain are sufficiently interrupted to result in a definite hypalgesia. After elimination of the endings of the long afferent systems in the ventral posterior thalamic nuclei, there are 3 areas where pain impulses may be integrated: in the mesencephalon, particularly its tectum, in the hypothalamus and in the cortex. The sensory cortex develops isolation phenomena following lesions of the ventral posterior nuclei but seems to play only an accessory role in the development of the thalamic syndrome, since its ablation does not abolish the thalamic pain. The cortical and mesencephalic integration of the pain impulses may play a part in determining the localization of the pain; but a tectal origin does not sufficiently explain certain features of the thalamic pain such as its response to emotions and the associated vegetative disturbances. It is, therefore, suggested that the entrance of pain conducting impulses into the hypothalamus plays an important role in the genesis of the Dejerine-Roussy syndrome. This view is supported by experiments showing that elimination of the ventral posterior thalamic nuclei is able to increase the potentials evoked in the hypothalamus by stimulation of afferent nerves.