Proprioception and Vibration Sensibility Discrimination in the Absence of the Posterior Columns

THE SENSORY system carried in the dorsal columns and medial lemniscus has been clearly shown by Mountcastle and others^1,2 to have the neurophysiological attributes essential for discriminative touch: its neurons are somatotopically organized at each successive level and subtend small contralateral peripheral receptive fields that are activated by mode specific mechanoreceptive stimuli. The security of synaptic transmission of this afferent information concerning the spatial and temporal sequence of stimuli is its most distinguishing feature. The ability to detect a change in the position of a limb and the ability to detect vibration have been considered functions of this sensory system.^3,4 Pathological lesions confined solely to the dorsal columns are believed to affect both modalities. However, there have been numerous reports of patients with dorsal funicular lesions in whom vibration sensibility and proprioception were not affected to the same degree, and many in whom no clinical deficit was