Exp Brain Res (1992) 91:484-488

Experimental BrainResearch 9 Springer-Verlag1992

Integration of multiple sensory modalities in cat cortex Mark T. Wallace t, M. Alex Meredith 2, and Barry E. Stein 1 1 Department of Physiology and 2 Department of Anatomy, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298-0551, USA Received March 10, 1992 / Accepted June 11, 1992

Summary. The results of this study show that the different receptive fields of multisensory neurons in the cortex of the cat anterior ectosylvian sulcus (AES) were in spatial register, and it is this register that determined the manner in which these neurons integrated multiple sensory stimuli. The functional properties of multisensory neurons in AES cortex bore fundamental similarities to those in other cortical and subcortical structures. These constancies in the principles o f multisensory integration are likely to provide a basis for spatial coherence in information processing throughout the nervous system.

Key words: Anterior ectosylvian sulcus - Multisensory integration - Visual - Somatosensory - Auditory

Introduction Higher organisms deal remarkably well with the task of integrating information f r o m the different sensory modalities. Indeed, a great deal of information has been generated concerning the perceptual effects of combining different sensory stimuli (Welch and Warren 1986). For this integration to occur, there must be sites at which information f r o m different sensory modalities converges. M a n y such sites exist in the vertebrate brain (e.g., see G o r d o n 1973; Drager and Hubel 1975; Hartline 1984; Stein 1984; Meredith and Stein 1986a). Presumably, however, such "higher order" functions as perception depend on integration in cortical neurons. Here, too, multisensory convergence is c o m m o n (see Albe-Fessard and Gillett 1961 ; D u b n e r and Rutledge 1964; Jones and Powell 1970; Pandya and Seltzer 1982). Unfortunately, very little is k n o w n a b o u t how sensory inputs are integrated in cortical neurons, or how this multisensory integration might ultimately contribute to perception. Correspondence to: M. Wallace

In the cat, the region of cortex surrounding the anterior ectosylvian sulcus (AES) has been described as a " p o lysensory" area, where inputs f r o m several sensory modalities converge (Graybiel 1972; Clemo and Stein 1982; R o d a and Reinoso-Suarez 1983; Reinoso-Suarez and R o d a 1985; Olson and Graybiel 1987; Meredith and Clemo 1989). Recent studies have shown that the AES is comprised o f three modality-specific regions: a visual area which lies on the ventral b a n k of the sulcus, the anterior ectosylvian visual area (AEV; Mucke et al. 1982; Olson and Graybiel 1987); a somatosensory area which lies toward the rostral pole o f the dorsal b a n k of the AES, the fourth somatosensory cortex (SIV; Clemo and Stein 1982); and an auditory area in the caudal regions of the dorsal bank, designated Field AES (Clarey and Irvine 1986). Near the borders of these unimodal regions are m a n y neurons that respond to more than one sensory modality (i.e., multisensory; Clemo et al. 1991). The purpose o f the present study was to explore how AES neurons deal with combinations of sensory cues from different modalities. Preliminary results of this work have appeared in abstract form (Meredith et al. 1991).

Materials and methods The procedures used here were similar to those described in detail by Meredith and Stein (1986a, b). Briefly, a recording well/headholding device was implanted over the AES in two deeply anesthetized cats (pentobarbital sodium 40 mg/kg i.p.), and animals recovered over 7-10 days. For recording, animals were anesthetized (halothane 0.75 2.0%) and paralyzed (pancuronium bromide 2 mg/kg per hour). The level of anesthesia was routinely monitored by assessing corneal reflexes during periods in which the animal was allowed to recover from paralysis. Once a neuron was isolated and the effective modalities determined, the receptive fields were mapped as follows: visual receptive fields were mapped using bars or spots of light from a pantoscope projected onto a translucent hemisphere; somatosensory receptive fields were mapped using a camel's hair brush or calibrated on Frey hairs; auditory receptive fields were mapped using broad-band noise bursts from a hoop-

485 mounted speaker. Quantitative sensory tests were conducted using computer-controlled stimuli, which included: deflections of the hair or skin using a modified Ling 102A shaker (somatosensory); broad-band noise bursts (auditory) ; and galvanometer-driven spots or bars of light (visual). Either these stimuli were delivered alone (e.g., visual only, auditory only) as a "single-modality test" or stimuli from two modalities were presented together (e.g., visual and auditory) in a "combined-modality test," using the temporal criteria of Meredith et al. (1987). Single- and combined-modality tests were conducted in an interleaved manner, with long (12-15 s) interstimulus intervals. The number of impulses evoked during single- and combined-modality tests were compared, and a multisensory interaction was defined as a significant difference (P

Integration of multiple sensory modalities in cat cortex.

The results of this study show that the different receptive fields of multisensory neurons in the cortex of the cat anterior ectosylvian sulcus (AES) ...
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