From a clinical and physiologic standpoint, lesions of a limited area, occurring at any level of the brain-stem, are of much interest. Any attempt to analyze the grouping of the afferent impulses in this region has always been attended with considerable difficulty. Impulses arising in the same peripheral system after reaching the first synaptic junction in the spinal cord are formed into groups by specific selection and by gradual filtration away into secondary tracts, and then traverse the cord, grouped according to their sensory qualities, in paths which are frequently isolated by disease.
All of those impulses underlying sensations of posture, passive movement and spatial discrimination, ascend in the ipsolateral dorsal tracts of the cord, grouped in such manner that lesions can not differentiate between the various components. All those impulses of a painful and thermal quality are grouped in the contralateral spinothalamic tracts and can be interrupted separately or