Abstract

A fundamental issue in quantitative neuromorphology is the extent to which processing demands affect the complexity of dendritic systems. To this end, the basilar dendritic systems of supragranular pyramidal cells in human supramodal association cortex (prefrontal, area 10) were compared with those in unimodal association cortex (occipital, area 18). Tissue obtained from the left hemisphere of 5 neurologically normal subjects was processed with a modified rapid Golgi technique. Quantification of 100 neurons (10 neurons per tissue block) was performed on a Neurolucida system (Microbrightfield, Inc.) according to accepted criteria (Jacobs & Scheibel, 1993, J. Comp. Neurol., 327, 83-96). Dependent measures were total dendritic length (TDL), mean dendritic length (MDL), dendritic segment count (DSC), and dendritic spine number (DSN). A distinction was also made between proximal (1st, 2nd, and 3rd order) and the ontogenetically later developing distal (4th order and above) dendritic branches.

Despite interindividual variation, neurons in area 10 consistently exhibited higher TDL (19.8%), DSC (19.9%), and DSN (31.6%) values than those in area 18. Proximal-distal distribution was similar between both cortical areas for TDL, DSC, and DSN, but distal segment MDL was an average of 79.6% greater than proximal segment MDL (which is consistent with Jacobs et al., 1993, J. Comp. Neurol., 327, 97-111). An order by order analysis of the dendritic envelope revealed that differences between the two cortical areas were most pronounced in 4th order dendritic segments. Significant age-related decreases in TDL, MDL, and DSN were also noted. This finding of greater dendritic neuropil in area 10 over area 18 provides tentative support in humans for the notion that dendritic system complexity roughly reflects the computational demands placed on those systems. (Tissue generously provided by Dr. D. Bowerman, El Paso County Coroner, and Dr. R. Sherwin, Penrose Hospital)

Back