Figure 8.

Diagram summarizing the morphological changes of withdrawing lemniscal axons (blue) from the upper limb and upper trunk representations in VPL after transection of the cuneate fasciculus. The same scheme applies to thalamocortical axons withdrawing from the upper limb and upper trunk representation in the somatosensory cortex. The first signs of transneuronal atrophy are a reduction in size and number of synaptic boutons, the presence of incomplete endings, and a loss of short terminal branches. The divergent projections of normal axons (red) from face and lower body representations to the adjacent cuneate representations, normally unable to drive activity, constitute the basis for the expansion of the silenced upper limb/upper trunk representation by adjacent representations of the face and lower body. In the long term, transneuronal atrophy, with shrinkage and loss of deafferented neurons, enhances the expansion of representations with intact innervation.