Spatial Determinants of Multisensory Integration In Cat Superior Colliculus
Meredith, M. Alex and Barry E. Stein.
Department of Anatomy, Medical College of Virginia, Virginia Commonwealth
University, Richmond, VA, Department of Neurobiology and Anatomy, Bowman Gray
School of Medicine, Wake Forest University, Winston-Salem, NC.
APStracts 2:0012N, 1996.
SUMMARY AND CONCLUSIONS
1. While a representation of multisensory space is contained in the superior
colliculus, little is known about the spatial requirements of multisensory
stimuli that influence the activity of neurons here. Critical to this problem
is an assessment of the registry of the different receptive fields within
individual multisensory neurons. The present study was initiated to determine
how closely the receptive fields of individual multisensory neurons are
aligned, the physiological role of that alignment, and the possible functional
consequences of inducing receptive field misalignment. 2. Individual
multisensory neurons in the superior colliculus of anesthetized, paralyzed
cats were studied using standard extracellular recording techniques. The
receptive fields of multisensory neurons were large, as reported previously,
but exhibited a surprisingly high degree of spatial coincidence. The average
proportion of receptive field overlap was 86% for the population of visual-
auditory neurons sampled. 3. Due to this high degree of intersensory receptive
field correspondence, combined-modality stimuli that were coincident in space
tended to fall within the excitatory regions of the receptive fields involved.
The result was a significantly enhanced neuronal response in 88% of the
multisensory neurons studied. If stimuli were spatially disparate, so that one
fell outside its receptive field, either a decreased response occurred (56%),
or no intersensory effect was apparent (44%) 4. The normal alignment of the
different receptive fields of a multisensory neuron could be disrupted by
passively displacing the eyes, pinnae, or limbs/body. In no case was a shift
in location or size observed in a neuron's other receptive field(s) to
compensate for this displacement. The physiological result of receptive field
misalignment was predictable and based on the location of the stimuli relative
to the new positions of their respective receptive fields. Now, for example,
one component of a spatially coincident pair of stimuli might fall outside its
receptive field and inhibit the other's effects. 5. These data underscore the
dependence of multisensory integrative responses on the relationship of the
different stimuli to their corresponding receptive fields rather than to the
spatial relationship of the stimuli to one another. Apparently, the alignment
of different receptive fields for individual multisensory neurons ensures that
responses to combinations of stimuli derived from the same event are
integrated to increase the salience of that event. Therefore, the maintenance
of receptive field alignment is critical for the appropriate integration of
converging sensory signals and, ultimately, elicitation of adaptive behaviors.
Received 8 December 1995; accepted in final form 16 November 1995.
APS Manuscript Number J769-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96