Strabismus (or squint) is both a well-established model for
developmental plasticity of the brain and a frequent clinical
symptom. While the layout and topographic relationship of
functional domains in area 17 of divergently squinting cats
has been analyzed extensively in recent years (e.g. Löwel
et al., 1998), functional maps in convergently squinting animals
have so far not been visualized with comparable detail. We have
therefore investigated the functional organization of area 17
in adult cats with a surgically induced convergent squint angle.
In these animals, visual acuity was determined by both behavioral
tests and recordings of visual evoked potentials, and animals
with comparable acuities in both eyes were selected for further
experiments. The functional layout of area 17 was visualized
using optical imaging of intrinsic signals. Monocular
iso-orientation domains had a patchy appearance and their layout
was different for left and right eye stimulation, so that
segregated ocular dominance domains could be visualized.
Iso-orientation domains exhibited a pinwheel-like organization,
as previously described for normal and divergently squinting
cats. Mean pinwheel density was the same in the experimental
and control animals (3.4 pinwheel centers per mm2
cortical surface), but significantly (P < 0.00001)
higher than that reported previously for normal and divergently
squinting cats (2.7/mm2). A comparison of orientation
with ocular dominance maps revealed that iso-orientation domains
were continuous across the borders of ocular dominance domains
and tended to intersect these borders at steep angles. However,
in contrast to previous reports in normally raised cats,
orientation pinwheel centers showed no consistent topographical
relationship to the peaks of ocular dominance domains. Taken
together, these observations indicate an overall similarity
between the functional layout of orientation and ocular dominance
maps in area 17 of convergently and divergently squinting cats.
The higher pinwheel densities compared with previous reports
suggest that animals from different gene pools might generally
differ in this parameter and therefore also in the space constants
of their cortical orientation maps.