# Show Reference: "A neural code for auditory space in the cat's superior colliculus"

A neural code for auditory space in the cat's superior colliculus The Journal of Neuroscience, Vol. 4, No. 10. (01 October 1984), pp. 2621-2634 by John C. Middlebrooks, Eric I. Knudsen
@article{middlebrooks-and-knudsen-1984,
abstract = {We have examined the intermediate and deep layers of the cat's superior colliculus for evidence of a neural representation of auditory space. We measured the responses of single units to sounds presented in a free field. The results support the following generalizations. Most auditory units in the superior colliculus have sharply delimited receptive fields which form two discrete classes distinguished by their locations and sizes. The remaining units respond to sounds presented at any location. Each auditory unit responds maximally to sounds at a particular horizontal and vertical location within its receptive field, the unit's  ” best area.” The best areas and receptive field borders of a unit are resistant to changes in the intensity of stimulus. The locations of best areas shift systematically as a function of unit position to form a continuous map of auditory space. The horizontal dimension of space is mapped rostrocaudally, and the vertical dimension is mapped mediolaterally. This map corresponds in orientation with the map of visual space. These data permit us to infer the distribution of unit activity elicited by a sound at any given location. Regardless of its location, a sound activates a substantial portion of the superior colliculus. Indeed, sounds at some locations activate nearly all of the auditory units. However the activated portion of the colliculus contains a restricted region of units which are excited to near their maximum firing rates. The position of this focus of greatest activity varies systematically according to the location of the sound source, thus mapping the location of the sound in space.},
author = {Middlebrooks, John C. and Knudsen, Eric I.},
citeulike-article-id = {13477815},
day = {01},
issn = {1529-2401},
journal = {The Journal of Neuroscience},
keywords = {auditory, biology, sc, sc-input},
month = oct,
number = {10},
pages = {2621--2634},
pmid = {6491727},
posted-at = {2015-01-08 15:02:46},
priority = {2},
publisher = {Society for Neuroscience},
title = {A neural code for auditory space in the cat's superior colliculus},
url = {http://www.jneurosci.org/content/4/10/2621.abstract},
volume = {4},
year = {1984}
}



Receptive fields of SC neurons in different modalities tend to overlap.

The response of neurons in the SC to a given stimulus decreases if that stimulus is presented constantly or repeatedly at a relatively slow rate (once every few seconds, up to a minute).

The superficial cat SC is not responsive to auditory stimuli.

Some neurons in the dSC respond to an auditory stimulus with a single spike at its onset, some with sustained activity over the duration of the stimulus.

Middlebrooks and Knudsen report on sharply delineated auditory receptive fields in some neurons in the deep cat SC, in which there is an optimal region from which stimuli elicit a stronger response than in other places in the RF.

A minority of deep SC neurons are omnidirectional, responding to sounds anywhere, albeit with a defined best area.

There is a map of auditory space in the deep superior colliculus.

There is considerable variability in the sharpness of spatial tuning in the responses to auditory stimuli of deep SC neurons.

Middlebrooks and Knudsen define a spatial receptive field of a neuron as that angular range from which a stimulus elicits any response above baseline.

The best area, on the other hand, is that range from which it a stimulus elicits at least 75% of the maximum response.

Middlebrooks and Knudsen note that other studies use different definitions.

ICx projects to intermediate and deep layers of SC.