Quantitative characteristics of the associative projections of field 4y to subfields of the sensorimotor and parietal cortex of the cat.

The Nauta-Gygax method was used to study the ipsilateral associative connections of motor cortex field 4y after local electrolytic lesioning of this zone. The relative quantitative distribution of associative fibers running from field 4y to somatosensory areas I and II, the motor cortex, and the parietal cortex was determined. The greatest projections of field 4y were found to be directed to field 2pri (the secondary somatosensory zone) and field 5ab. Occasional degenerative fibers passed to fields 1, 2, 3a, and 3b of the primary somatosensory zone of the cortex. Efferent fibers from field 4y were not directed to fields 4fu, 4sfu, 6aa, 6ab, or 6ifu. It is suggested that the morphological basis of motor reactions mediated by field 4y is not provided by the fundal (4fu, 4sfu, 6ifu) or premotor (6aa, 6ab) fields but by field 2pri and 5ab, with which it has more extensive connections.