QUANTITATIVE INVESTIGATIONS ON THE HUMAN ENTORHINAL AREA - LEFT-RIGHTASYMMETRY AND AGE-RELATED-CHANGES

The total nerve cell numbers in the right and in the left human entorh inal areas have been calculated by volume estimations with the Cavalie ri principle and by cell density determinations with the optical disec tor. Thick gallocyanin-stained serial frozen sections through the para hippocampal gyrus of 22 human subjects (10 female, 12 male) ranging fr om 18 to 86 years were analysed. The laminar composition of gallocyani n (Nissl)-stained sections could easily be compared with Braak's (1972 , 1980) pigmentoarchitectonic study, and Braak's nomenclature of the e ntorhinal laminas was adopted. Cell-sparse laminae dissecantes can mor e clearly be distinguished in Nissl than in aldehydefuchsin preparatio ns. These cell-poor dissecantes, lamina dissecans externa (dis-ext), l amina dissecans 1 (dis-1) and lamina dissecans 2 (dis-2), were exclude d from nerve cell number determinations. An exact delineation of the e ntorhinal area is indispensable for any kind of quantitative investiga tion. We have defined the entorhinal area by the presence of pre-alpha cell clusters and the deeper layers of lamina principalis externa (pr e-beta and gamma) separated from lamina principalis interna (pri) by l amina dissecans 1 (dis-1). The human entorhinal area is quantitatively characterized by a left-sided (asymmetric) higher pre-alpha cell numb er and an age-related nerve cell loss in pre as well as pri layers. At variance with other CNS cortical and subcortical structures, the neur onal number of the entorhinal area appears to decrease continuously fr om the earliest stages analysed, although a secular trend has to be co nsidered. The asymmetry in pre-alpha cell number is discussed in the c ontext of higher human mental capabilities, especially language.