Post-natal development of the retinal and cerebellar projections onto the lateral suprasylvian area in the cat.

1. Post-natal development of the retinal and cerebellar projections onto the medial bank of the lateral suprasylvian visual area was examined by using the field potential method and, additionally, by the orthograde horseradish peroxidase method. 2. Optic nerve stimulation elicited a surface-positive, depth-negative field potential in the medial bank of the lateral suprasylvian area of adult cats. By contrast, in kittens younger than 3 weeks old, a surface-negative, depth-positive field potential was evoked. The response grew adult-like by 1 month of age. Corticocortical response, activated by stimulation of cortical areas 17 and 18, underwent a similar developmental change. 3. Cerebellar stimulation evoked a surface-negative, depth-positive wave from birth up to adulthood. Thalamocortical afferents from the ventroanterior and ventrolateral nuclei of the thalamus to the medial bank of the lateral suprasylvian area, which is presumed to be responsible for this cerebellar response, terminate mostly in layer I in both new-born kittens and adult cats. 4. The present results, and our previous morphological findings on the projections from the extrageniculate visual thalamus and visual cortical areas 17 and 18 onto the medial bank of the lateral suprasylvian area, were correlated with reference to the maturation of the neuronal circuit in the cortex.