A comparison of the number of neurons in individual laminae of cortical areas 17, 18 and posteromedial suprasylvian (PMLS) area in the cat.

The binocular region of area 17 (17B) has a greater number of neurons under a given unit of cortical surface (NC, number per column) than either the monocular region of area 17 (17M), area 18 or the posteromedial suprasylvian area (PMLS). The latter three areas follow the general principle of basic uniformity in the number of neurons under given units of cortical surface formulated by Rockel et al. This basic uniformity is maintained in layers I and II. The NC of other layers varies. The greatest differences are found in layer IV where the NC of each area is significantly different from that of each other area. Though the difference between layer IV of 17M and of either 18 and PMLS is largely offset by changes in the third layer, layers V (PMLS) and VI (18 and PMLS) also contribute to the compensation. The compensation between 18 and PMLS is due entirely to changes in layer VI. It is important to note that there are statistically demonstrable interindividual differences in the neuronal NC of the cats used in the present study. We suggest that these may be due to age, breeding, or rearing conditions, probably the latter.