Hemispheric differences in layer III pyramidal neurons of the anterior language area
T. L. Hayes and D. A. Lewis
Department of Behavioral Neuroscience, University of Pittsburgh, PA 15213.
OBJECTIVE--The major objective of this study was to determine if the
lateralization of motor speech functions may be associated with hemispheric
differences in the size of layer III pyramidal neurons in Brodmann's area
45. DESIGN--A case series design involving postmortem human specimens was
used to compare the cross-sectional area of NissI-stained layer III
pyramidal neurons of Brodmann's area 45 from the left and right
hemispheres. SUBJECTS--A convenience sample consisting of seven cases with
no known neurological or psychiatric disorders was obtained at autopsy.
MAIN OUTCOME MEASURES--The cross-sectional area of layer III pyramidal
neurons in both left and right hemispheres was measured in four fields per
hemisphere per brain using a computerized image analysis system.
Measurements of both the largest layer III pyramids and of all layer III
pyramids were done. RESULTS--The largest layer III pyramidal neurons of
area 45 were significantly larger in the left than in the right hemisphere
in both an unblinded and a blinded series of measurements. However, this
hemispheric difference appeared to be restricted to the largest neurons,
since the mean size of all layer III pyramids in this area was not
significantly different in the left and right hemispheres. CONCLUSIONS--The
presence of a unique population of large pyramidal neurons in left
Brodmann's area 45 may be related to the involvement of this region in the
circuitry that mediates motor speech functions.
