Pyramidal cells of the frontal lobe: All the more spinous to think with

The basal dendritic arbors of pyramidal cells in prefrontal areas 10, 11, a nd 12 of the macaque monkey were revealed by intracellular injection in fix ed, flat-mounted, cortical slices. The size, number of branches, and spine density of the basal dendrites were quantified and compared with those of p yramidal cells in the occipital, parietal, and temporal lobes. These analys es revealed that cells in the frontal lobe were significantly more spinous than those in the other lobes, having as many as 16 times more spines than cells in the primary visual area (V1), four times more those in area 7a, an d 45% more than those in area TE. As each dendritic spine receives at least one excitatory input, the large number of spines reported for layer III ce lls in prefrontal cortex suggests that they are capable of integrating a gr eater number of excitatory inputs than layer III pyramidal cells so far stu died in the occipital, parietal, and temporal lobes. The ability to integra te a large number of excitatory inputs may be important for the sustained t onic activity characteristic of neurons in prefrontal cortex and their role in memory and cognition.