A quantitative dendritic analysis of Wernicke's area in humans. I. Lifespan changes

Age-related increases and decreases have been described in cortical dendritic neuropil. Here, we examine age-related changes in the basilar dendrites of supragranular pyramidal cells in human superior temporal gyrus (i.e., Wernicke's area) of left and right hemispheres. Tissue was obtained from 20 neurologically normal right-handers from 18-79 years: 10 males (Mage = 52.2 years; SDage = 17.4) and 10 females (Mage = 47.8; SDage = 20.5). In tissue prepared by a modified rapid Golgi technique, ten pyramidal cells were sampled from each hemisphere and evaluated according to the following parameters: total dendritic length, mean dendritic length, and dendritic segment count. Despite considerable interindividual variation, the data exhibited significant dendritic degeneration with aging. There was an age-related decrease in total dendritic length (r[20] = -0.44; P < 0.05) and especially in mean dendritic length (r[20] = -0.69; P < 0.001) with increasing age. Age-mean dendritic length correlations were negative for all segment orders and revealed a progressive decrease in segment length in more distal branches. The number of dendritic segments remained relatively stable across the age span sampled. The data also indicated that interhemispheric dendritic asymmetries decreased with age. Individuals under 50 years of age had significantly greater total dendritic length values in the left hemisphere. Interhemispheric dendritic differences were not significant in individuals over 50.