Arbor Vitae wide-field view of the superior cerebellar peduncle axonal pathway

Left. The brain is seen from below, with the olfactory bulbs at the top. Three sets of bilaterally represented gray matter nuclei are displayed as clouds of dots: the cerebellar lateral, interpositus and medial nuclei faintly visible in blue-green (arrows), the red nuclei of the midbrain in red, and the ventral lateral nuclei of the thalamus in yellow.

Right. Simulated axons of the superior cerebellar peduncle arise from neuron cell bodies in the cerebellar lateral and interpositus nuclei, decussate in the caudal half of the midbrain, pass under and lateral to the red nuclei in the rostral part of the midbrain, innervate red nucleus neurons, and then pass rostrally to the ventrolateral nucleus of the thalamus. This, to our knowledge, is the first rendition of axonal trajectories in 3D brain maps. The method is in its first phase, and at present, axons are instructed to "grow" from structure A to structure B. They have not yet "learned" not to arise from the medial nuclei of the cerebellum, only from the other deep nuclei, nor precisely how to skirt the red nucleus rather than penetrate through it. In future it should be possible to have axons grow along precisely delimited trajectories set by the already-plotted white matter tracts. In the animated version of the present program, as dispalayed on the SGI Octane computer, not only does one observe the extension of the axons from A to B as a function of time, but once grown, they have been simulated to show bright flashes of "nerve impulses" in the physiological direction Ñ in this case, from cerebellum to thalamus.