Interlaminar differences in the pyramidal cell phenotype in cortical areas7m and STP (the superior temporal polysensory area) of the macaque monkey

Pyramidal neurones were injected with Lucifer Yellow in slices cut tangenti al to the surface of area 7m and the superior temporal polysensory area (ST P) of the macaque monkey. Comparison of the basal dendritic arbors of supra - and infragranular pyramidal neurones (n=139) that were injected in the sa me putative modules in the different cortical areas revealed variation in t heir structure. Moreover, there were relative differences in dendritic morp hology of supra- and infragranular pyramidal neurones in the two cortical a reas. Shell analyses revealed that layer III pyramidal neurones in area STP had considerably higher peak complexity (maximum number of dendritic inter sections per Shell circle) than those in layer V, whereas peak complexities were similar for supra- and infragranular pyramidal neurones in area 7m. I n both cortical areas, the basal dendritic trees of layer m pyramidal neuro nes were characterized by a higher spine density than those in layer V. Cal culations of the total number of dendritic spines in the "average" basal de ndritic arbor revealed that layer V pyramidal neurones in area 7m had twice as many spines as cells in layer III. (4535 and 2294, respectively). A sim ilar calculation for neurones in area STP revealed that layer III pyramidal neurones had approximately the same number of spines as cells in layer V ( 3585 and 3850 spines, respectively). Relative differences in the branching patterns of, and the number of spines in, the basal dendritic arbors of sup ra- and infragranular pyramidal neurones in the different cortical areas ma y allow for integration of different numbers of inputs, and different degre es of dendritic processing. These results support the thesis that intra-are al circuitry differs in different cortical areas.