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Updated: Aug 8, 2026
Functional Imaging of Auditory Cortex in Adult Cats using High-field fMRI
Published on: February 19, 2014
Bimodal interactions in the superior colliculus of the behaving cat
1Department of Anatomy, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA. lpopulin@facstaff.wisc.edu
Insights
Bimodal enhancement in the superior colliculus (SCi) was not observed in behaving cats, contrary to findings in anesthetized animals. Instead, auditory and visual stimuli primarily caused depressive effects, especially during visual fixation tasks.
Area of Science:
- Neuroscience
- Sensory processing
- Auditory-visual integration
Background:
- Bimodal enhancement, a nonlinear summation of responses to stimuli from two sensory modalities, is theorized to underlie behavioral facilitation.
- Previous studies demonstrating this phenomenon were conducted in anesthetized animals, primarily in the superior colliculus intermediate layers (SCi).
Purpose of the Study:
- To investigate the presence of bimodal enhancement in the SCi of behaving animals.
- To determine if neural mechanisms for behavioral facilitation exist between auditory and visual modalities in awake, behaving subjects.
Main Methods:
- Behavioral experiments were conducted on cats trained to respond to acoustic, visual, and bimodal stimuli.
- Variations in stimulus timing and intensity were employed to elicit bimodal enhancement.
- Three distinct behavioral paradigms were utilized to assess cross-modal interactions.
Main Results:
- Contrary to expectations, no evidence of bimodal enhancement was observed in the SCi of behaving cats.
- Significant depressive effects were noted, particularly when acoustic stimuli were presented during visual fixation.
- Stimulus timing and intensity adjustments did not yield enhanced responses.
Conclusions:
- The findings challenge the prevailing notion that bimodal enhancement in the SCi is a primary neural mechanism for behavioral facilitation in awake animals.
- Auditory-visual interactions in the SCi may be characterized by suppression rather than enhancement under certain behavioral conditions, such as during focused visual attention.
Abstract:
Bimodal enhancement, a form of nonlinear summation of physiological responses from two sensory modalities, has been demonstrated in the intermediate layers of the superior colliculus (SCi) and is thought to be a manifestation of a neural mechanism underlying behavioral facilitation to such stimuli. Most physiological studies, however, have been performed in anesthetized animals. We tested for bimodal enhancement in the SCi of behaving cats trained to orient to acoustic, visual, and bimodal stimuli. Surprisingly, we never observed the large enhanced responses reported in anesthetized animals, even when we varied the time between presentation of the visual and acoustic stimuli and/or decreased the level of the stimuli. Using three different behavioral paradigms, we found no support for enhanced interactions between auditory and visual modalities. Prominent depressive effects were seen, however, particularly when the cats were required to fixate a visual target during presentation of an acoustic stimulus.
