Laminar specificity of intrinsic connections in Broca's area.
Broca's area and its right hemisphere homologue comprise 2 cytoarchitectonic subdivisions, FDgamma and FCBm of von Economo C and Koskinas GN (1925, Die Cytoarchitektonik der Hirnrinde des erwachsenen Menschen. Vienna/Berlin [Germany]: Springer). We report here on intrinsic connections within these areas, as revealed with biotinylated dextran amine and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate tracing in postmortem human brains. Injections limited to supragranular layers revealed a complex intrinsic network of horizontal connections within layers II and III spreading over several millimeters and to a lesser extent within layers IV, V, and VI. Ninety percent of the retrogradely labeled neurons (n = 734) were in supragranular layers, 4% in layer IV, and 6% in infragranular layers; most were pyramids and tended to be grouped into clusters of approximately 500 microm in diameter. Injections involving layer IV revealed extended horizontal connections within layers I-IV (up to 3.7 mm) and to a lesser extent in layers V and VI. Injections limited to the infragranular layers revealed horizontal connections mainly limited to these layers. Thus, intrinsic connections within Broca's area display a strong laminar specificity. This pattern is very similar in areas FDgamma and FCBm and in the 2 hemispheres.
Tardif
Eric
E
Service de Neuropsychologie et de Neuroréhabilitation, CHUV, Université de Lausanne, CH-1011 Lausanne, Switzerland.
Probst
Alphonse
A
Clarke
Stephanie
S
D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005625:Frontal Lobe / Q000166:cytology*; D006801:Humans; D008297:Male; D009415:Nerve Net / Q000166:cytology*; D009434:Neural Pathways / Q000166:cytology*