Figure 6.

Axon tracing from electrophysiologically characterized regions of VP. A, The electrode was inserted into the brain from the occipital pole and advanced after a horizontal trajectory. Multiunit evoked responses from multiple electrode penetrations were used to identify the somatotopic map in VP. B, Circles represent tracks left by an array of electrode penetrations, reconstructed from a series of coronal sections through the posterior thalamus. Track colors represent the portion of periphery from which evoked activity could be recorded. The majority of sites in the hand representation (blue) were silenced by the spinal lesion. Arrowheads point to labeled axons. Axons reconstructed from the deafferented hand field (between blue tracks t11 and t12) were compared with axons terminating in the leg/lower body area (between green tracks t5 and t10). C, D, Line rendering of lemniscal axon tracings from deafferented (C) and normal (D) VPL, showing the intrinsic size of synaptic boutons (varicosities). Scale bar in D applies also to C. E, Frequency distributions of varicosity sizes in the two groups of axons. The average reduction of varicosity size in deafferented VPL was 31.8% (Wald = 22.740, p < 0.001, Exp(B) = 0.000).