Interlaminar connections of tree shrew visual cortex.

The intracortical projections of neurons in layers II and upper III of tree shrew visual cortex were studied after terminal lesions in the supragranular layers of area 17. Examination for terminal degeneration was made using ultrastructural techniques. The majority of degenerating terminals were found in layers V and, to a lesser extent, VI, and were presynaptic to neural profiles in the following distribution: 80.5% on spines of small to medium size dendrites, 19% on dendrite shafts, and less than 1% on neuronal perikarya. Degenerating axons coursed in vertical bundles through layers III, IV, V and VI. These findings are similar to those previously described in rat visual cortex.