Journal of Neuroscience, Vol 10, 3727-3742, Copyright © 1990 by Society for Neuroscience
The visuotopic component of the multisensory map in the deep laminae of the cat superior colliculus
MA Meredith and BE Stein
Department of Anatomy, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298.
A well-defined map of visual space is located in the deep laminae of the
cat superior colliculus. The horizontal meridian is oriented
rostral-caudal, while the vertical meridian is oriented perpendicular to it
in the rostral third of the structure. This map represents the entire
contralateral visual field and extends approximately 40 degrees into
ipsilateral visual space. Although the deep-laminae visuotopy is similar to
that found in the superficial laminae of the same structure, the
topographic register among these maps is most secure rostrally but becomes
increasingly poorer at more caudal and lateral locations. The combination
of 2 features distinguish the deep-layer visual representation from that
found in the superficial laminae and in geniculocortical systems: (1) the
constituent visual receptive fields are very large (mean diameter, 66.9
degrees), and (2) the majority (greater than 70%) of the neurons composing
it receive nonvisual inputs. Because the visual receptive fields of
visual-multisensory neurons are significantly larger than those of
neighboring neurons that respond only to visual stimuli, far more
visual-multisensory neurons are activated by any given visual stimulus.
These data, when coupled with those from previous studies, suggest that,
from a functional perspective, deep-laminae visual neurons form one
component of an integrated multisensory map, and that their topographic
organization is essential for the normal dynamics of multisensory
integration.