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Neuronal Size and Neuronal-Packing Density in Primary Visual Cortex

Albert M. Galaburda, MD; Dorothy P. Holinger, PhD; Ursula Bellugi, EdD; Gordon F. Sherman, PhD

Arch Neurol. 2002;59:1461-1467.

Background  Williams syndrome (WMS) is a rare, genetically based syndrome associated with a hemideletion in chromosome 7 (7q11.22-23) and characterized by a unique constellation of somatic, brain, and cognitive features. Individuals with WMS demonstrate an unusual and uneven neuropsychological profile showing cognitive and visual spatial deficits juxtaposed with relative language preservation and excellent facial recognition.

Objectives  A neuroanatomical hypothesis for these behavioral findings suggests predominant involvement of the dorsal portions of the hemispheres relative to the ventral portions, including preferential involvement of peripheral visual field cortical representations over central representation. Predominant involvement of magnocellular visual pathways, as opposed to parvocellular pathways, is also suggested by this hypothesis.

Subjects  We examined primary visual cortical area 17 in the right and left hemispheres in 6 age- and sex-matched autopsy specimens from 3 WMS-affected brains (1 male and 2 females; mean [SD] age, 44 [14] years) and 3 control brains (1 male and 2 females; mean age, 43 [11] years).

Design  Neurons in layers II, III, IVA, IVB, IVC, IVCß, V, and VI were measured using an optical dissector method to determine possible differences between WMS-affected and control brains in cell-packing density, neuronal size, and neuronal size distribution.

Results  We found abnormalities in peripheral visual cortex in WMS-affected brains, but not in magnocellular subdivisions. There was a hemisphere by layer IV interaction and a layer IV left hemisphere and diagnosis interaction in cell-packing density. Williams syndrome–affected brains showed increased cell-packing density in left sublayer IVCß and an excess of small neurons in left layers IVA, IVC, IVCß, V, and VI.

Conclusions  Cell measurements differ in peripheral visual cortical fields of WMS, with significantly smaller, more closely packed cells in some layers on the left side. These cell-packing density and neuronal size differences may be related to visuospatial deficits in this population.

From the Division of Behavioral Neurology, Departments of Neurology (Drs Galaburda and Holinger) and Psychiatry (Dr Holinger), Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Mass; Laboratory for Cognitive Neuroscience, The Salk Institute for Biological Studies, La Jolla, Calif (Dr Bellugi); and The Newgrange School Educational Outreach Center, Princeton, NJ (Dr Sherman).

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