# Show Reference: "Mechanisms of Within- and Cross-Modality Suppression in the Superior Colliculus"

Mechanisms of Within- and Cross-Modality Suppression in the Superior Colliculus Journal of Neurophysiology, Vol. 78, No. 6. (1 December 1997), pp. 2834-2847 by Daniel C. Kadunce, J. William Vaughan, Mark T. Wallace, Gyorgy Benedek, Barry E. Stein
@article{kadunce-et-al-1997,
abstract = {Kadunce, Daniel C., J. William Vaughan, Mark T. Wallace, Gyorgy Benedek, and Barry E. Stein. Mechanisms of within- and cross-modality suppression in the superior colliculus. J. Neurophysiol. 78: 2834–2847, 1997. The present studies were initiated to explore the basis for the response suppression that occurs in cat superior colliculus ({SC}) neurons when two spatially disparate stimuli are presented simultaneously or in close temporal proximity to one another. Of specific interest was examining the possibility that suppressive regions border the receptive fields ({RFs}) of unimodal and multisensory {SC} neurons and, when activated, degrade the neuron's responses to excitatory stimuli. Both within- and cross-modality effects were examined. An example of the former is when a response to a visual stimulus within its {RF} is suppressed by a second visual stimulus outside the {RF}. An example of the latter is when the response to a visual stimulus within the visual {RF} is suppressed when a stimulus from a different modality (e.g., auditory) is presented outside its (i.e., auditory) {RF}. Suppressive regions were found bordering visual, auditory, and somatosensory {RFs}. Despite significant modality-specific differences in the incidence and effectiveness of these regions, they were generally quite potent regardless of the modality. In the vast majority (85\%) of cases, responses to the excitatory stimulus were degraded by ≥50\% by simultaneously stimulating the suppressive region. Contrary to expectations and previous speculations, the effects of activating these suppressive regions often were quite specific. Thus powerful within-modality suppression could be demonstrated in many multisensory neurons in which cross-modality suppression could not be generated. However, the converse was not true. If an {extra-RF} stimulus inhibited center responses to stimuli of a different modality, it also would suppress center responses to stimuli of its own modality. Thus when cross-modality suppression was demonstrated, it was always accompanied by within-modality suppression. These observations suggest that separate mechanisms underlie within- and cross-modality suppression in the {SC}. Because some modality-specific tectopetal structures contain neurons with suppressive regions bordering their {RFs}, the within-modality suppression observed in the {SC} simply may reflect interactions taking place at the level of one input channel. However, the presence of modality-specific suppression at the level of one input channel would have no effect on the excitation initiated via another input channel. Given the modality-specificity of tectopetal inputs, it appears that cross-modality interactions require the convergence of two or more modality-specific inputs onto the same {SC} neuron and that the expression of these interactions depends on the internal circuitry of the {SC}. This allows a cross-modality suppressive signal to be nonspecific and to degrade any and all of the neuron's excitatory inputs.},
address = {Department of Neurobiology and Anatomy, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27157, USA.},
author = {Kadunce, Daniel C. and Vaughan, J. William and Wallace, Mark T. and Benedek, Gyorgy and Stein, Barry E.},
citeulike-article-id = {411545},
day = {1},
issn = {0022-3077},
journal = {Journal of Neurophysiology},
keywords = {enhancement, multi-modality, sc, suppression},
month = dec,
number = {6},
pages = {2834--2847},
pmid = {9405504},
posted-at = {2011-07-14 10:55:25},
priority = {2},
title = {Mechanisms of Within- and {Cross-Modality} Suppression in the Superior Colliculus},
url = {http://jn.physiology.org/content/78/6/2834.abstract},
volume = {78},
year = {1997}
}



Reactions to cross-sensory stimuli can be faster than the fastest reaction to any one of the constituent uni-sensory stimuli (as would be predicted by the race model.).

The neural response of an SC neuron to one stimulus can be made weaker in some neurons by another stimulus at a different position in space. This stimulus can be in the same or in a different modality (in multi-sensory neurons). This effect is called depression.

Kadunce et al. did not find within-modality visual suppression as often as within-modality auditory suppression.

Kadunce et al. found that suppressive regions were large and that depression varied depending on position of the concurrent stimulus within the suppressive region. Suppression was generally strongest when concurrent stimuli were on the ipsilateral side.

Two identical stimuli at different locations can be perceived as one stimulus which seems to be located between the actual sound sources.

Kadunce et al. say that two identical stimuli played at different points in space might lead to a translocation of the perceived stimulus and thus to a translocation of the hill of activation in the SC.

Kadunce et al. found that two auditory stimuli placed at opposing the edges of a neuron's receptive field, in its suppressive zone, elicited some activity in the neuron (although less than they expected).

Kadunce et al. found cross-modality depression less often than within-modality depression.

Kadunce et al. found that for the majority of neurons in which a stimulus in one modality could lead to depression in another modality that depression was one-way: Stimuli in the second modality did not depress responses to stimuli in the first.

Kadunce et al. found that SC neurons are very inhomogeneous wrt. to presence and size of suppressive zones.

Multiplying probabilities is equivalent to adding their logs. Thus, working with log likelihoods, one can circumvent the necessity of neural multiplication when combining probabilities.

Multisensory integration, however, has been viewed as integration of information in exactly that sense, and it is well known that multisensory neurons respond super-additively to stimuli from different modalities.

Enhancement is greatest for weak stimuli and least for strong stimuli. This is called inverse effectiveness.