Journal of Neurophysiology, Vol 53, Issue 3 726-745, Copyright © 1985 by APS

ARTICLES

Responses of neurons in the cat's superior colliculus to acoustic stimuli. I. Monaural and binaural response properties

J. A. Hirsch, J. C. Chan and T. C. Yin

Using extracellular electrodes we studied acoustic responses in the superior colliculus (SC) of the barbiturate-anesthetized cat. Pure tonal stimuli were delivered through sealed and calibrated earphones and were presented either monaurally or binaurally with interaural intensity differences (IIDs) and interaural time differences (ITDs). Acoustically sensitive cells were found in the intermediate and deep layers of the SC throughout its rostrocaudal and mediolateral extent. Most cells (80%) discharged only at stimulus onset; the rest had more complex firing patterns. For 88% of our sample the mean first-spike latency measured at 20 dB above threshold ranged between 6 and 16 ms. The sharpness and threshold intensity of the frequency tuning curves varied widely. In the SC, the average characteristic frequency and threshold intensity were higher than in other auditory brain stem nuclei. Neurons whose characteristic frequency was low were never sharply tuned. The probability of response decreased when the repetition rate at which the stimuli were delivered increased. The mean stimulus interval at which spike count reached 50% of maximum was 360 ms. Most (83%) of the cells discharged only to monaural stimulation of the contralateral ear, 7% responded to tones applied to either ear and only 1% to only ipsilateral input. The remaining cells responded only to stimulation of both ears. With binaural stimuli, most neurons (80%) could be shown to receive input from both ears. Seventy percent of the binaural cells showed predominant binaural inhibition (BI), 25% binaural facilitation (BF), and 5% a more complex mixture. Because the majority of SC neurons had high characteristic frequencies, we examined their responses to IIDs. The spike count vs. IID functions of BI cells were monotonic and sigmoidal, those of BF cells were nonmonotonic and bell-shaped. The slopes and horizontal positions of the curves varied among neurons. IIDs favoring the contralateral ear were the most effective. For a given cell, increasing the mean binaural level extended the range of IIDs that evoked maximal discharge. A small number of cells was sensitive to physiologically significant interaural time differences of low-frequency tones or the envelopes of amplitude-modulated, high-frequency tones.

This article has been cited by other articles:

				E. Saldana, A. Vinuela, A. F. Marshall, D. C. Fitzpatrick, and M.-A. Aparicio The TLC: A Novel Auditory Nucleus of the Mammalian Brain J. Neurosci., November 28, 2007; 27(48): 13108 - 13116. [Abstract] [Full Text] [PDF]

				R. A. A. Campbell, T. P. Doubell, F. R. Nodal, J. W. H. Schnupp, and A. J. King Interaural Timing Cues Do Not Contribute to the Map of Space in the Ferret Superior Colliculus: A Virtual Acoustic Space Study J Neurophysiol, January 1, 2006; 95(1): 242 - 254. [Abstract] [Full Text] [PDF]

				L. C. Populin Anesthetics Change the Excitation/Inhibition Balance That Governs Sensory Processing in the Cat Superior Colliculus J. Neurosci., June 22, 2005; 25(25): 5903 - 5914. [Abstract] [Full Text] [PDF]

				P. Poirier, F. K. Samson, and T. J. Imig Spectral Shape Sensitivity Contributes to the Azimuth Tuning of Neurons in the Cat's Inferior Colliculus J Neurophysiol, May 1, 2003; 89(5): 2760 - 2777. [Abstract] [Full Text] [PDF]

				L. C. Populin and T. C. T. Yin Bimodal Interactions in the Superior Colliculus of the Behaving Cat J. Neurosci., April 1, 2002; 22(7): 2826 - 2834. [Abstract] [Full Text] [PDF]

				F. K. Samson, P. Barone, W. A. Irons, J. C. Clarey, P. Poirier, and T. J. Imig Directionality Derived From Differential Sensitivity to Monaural and Binaural Cues in the Cat's Medial Geniculate Body J Neurophysiol, September 1, 2000; 84(3): 1330 - 1345. [Abstract] [Full Text] [PDF]

				T. J. Anastasio, P. E. Patton, and K. Belkacem-Boussaid Using Bayes' Rule to Model Multisensory Enhancement in the Superior Colliculus Neural Comput., May 1, 2000; 12(5): 1165 - 1187. [Abstract] [Full Text]

				J. J. Eggermont Azimuth Coding in Primary Auditory Cortex of the Cat. II. Relative Latency and Interspike Interval Representation J Neurophysiol, October 1, 1998; 80(4): 2151 - 2161. [Abstract] [Full Text] [PDF]

				E. I. Knudsen Capacity for Plasticity in the Adult Owl Auditory System Expanded by Juvenile Experience Science, March 6, 1998; 279(5356): 1531 - 1533. [Abstract] [Full Text]

				J. W. H. Schnupp, A. J. King, and S. Carlile Altered Spectral Localization Cues Disrupt the Development of the Auditory Space Map in the Superior Colliculus of the Ferret J Neurophysiol, February 1, 1998; 79(2): 1053 - 1069. [Abstract] [Full Text] [PDF]

				D. C. Kadunce, J. W. Vaughan, M. T. Wallace, G. Benedek, and B. E. Stein Mechanisms of Within- and Cross-Modality Suppression in the Superior Colliculus J Neurophysiol, December 1, 1997; 78(6): 2834 - 2847. [Abstract] [Full Text] [PDF]

				J. W. H. Schnupp and A. J. King Coding for Auditory Space in the Nucleus of the Brachium of the Inferior Colliculus in the Ferret J Neurophysiol, November 1, 1997; 78(5): 2717 - 2731. [Abstract] [Full Text] [PDF]

				T. J. Park, P. Monsivais, and G. D. Pollak Processing of Interaural Intensity Differences in the LSO: Role of Interaural Threshold Differences J Neurophysiol, June 1, 1997; 77(6): 2863 - 2878. [Abstract] [Full Text] [PDF]