Stereological study of pyramidal neurons in the human superior temporal gyrus from childhood to adulthood.

The association cortex of the superior temporal gyrus (STG) is implicated in complex social and linguistic functions. Thus, reliable methods for quantifying cellular variation in this region could greatly benefit researchers interested in addressing the cellular correlates of typical and atypical function associated with these critical cognitive abilities. To facilitate this task, we first present a general set of cytoarchitectonic criteria targeted specifically toward stereological analyses of thick, Nissl-stained sections for the homotypical cortex of the STG, referred to here as BA22/TA. Second, we use the optical fractionator to estimate pyramidal neuron number and the nucleator for pyramidal somal and nuclear volume. We also investigated the influence of age and sex on these parameters, as well as set a typically developing baseline for future comparisons. In 11 typically developing cases aged 4-48 years, the most distinguishing features of BA22/TA were the presence of distinct granular layers, a prominent, jagged layer IIIc, and a distinctly staining VIa. The average number of neurons was 91 ± 15 million, the volume of pyramidal soma 1,512 µm(3) , and the nuclear volume 348 µm(3) . We found no correlation with age and neuron number. In contrast, pyramidal somal and nuclear volume were both negatively correlated and linearly associated with age in regression analyses. We found no significant sex differences. Overall, the data support the idea that postnatal neuron numbers are relatively stable through development but also suggest that neuronal volume may be subject to important developmental variation. Both measures are critical variables in the study of developmental neuropathology.