PIGMENT ARCHITECTURE OF THE HUMAN FRONTAL-LOBE .1. PRECENTRAL, SUBCENTRAL AND FRONTAL REGION

The precentral, subcentral, and frontal region of the human frontal lobe were examined by means of stereomicroscopical analysis using 800 μm thick pigment preparations. The precentral region can be divided into markedly externoteniate ganglionic core fields and weakly externoteniate paraganglionic belt areas. The core fields are in addition characterized by a conspicuous population of pigment-laden Betz-pyramids in layer pVb. A typical pattern of pigmentation permits their clear distinction from other pyramidal cells of the fifth layer. When passing to the paraganglionic belt areas devoid of Betz-pyramids, the uniform multiform layer splits into a strongly pigmented pVIa and a more pallid pVIb. The subcentral region at the lowermost extremity of the central sulcus displays features of both frontal and parietal areas. The frontal region is mainly formed of equoteniate areas but comprises also a tongue-shaped internoteniate territory medially and an elongated externoteniate area laterally. Extended parts of the frontal region which abut upon the paraganglionic belt are endowed with unusually large and pigmentladen IIIc-pyramids. Pyramids of this type can be rarely encountered within the human isocortex but occur in great number in circumscribed specialized regions such as the temporal magnopyramidal region which represents probably the speech centre of Wernicke. Within the frontal lobe, two magnopyramidal regions can be distinguished. The superofrontal magnopyramidal region stretches out over large parts of the superior frontal convolution whereas the inferofrontal one is small and covers mainly posterior parts of the inferior frontal gyrus. As to its location, the superofrontal magnopyramidal region includes the supplementary motor region which is known to be involved in the performance of speech. On account of its unique structure and its location, the inferofrontal magnopyramidal region is considered to represent the morphological counterpart of the speech centre of Broca. © 1979 Springer-Verlag.