Type III units in the gerbil dorsal cochlear nucleus may be spectral notchdetectors

Broadband sounds originating in the median plane are thought to be localize d by neural processing of spectral notches introduced by the filtering acti on of the pinnae. Previous studies (Nelken, I., and E. D. Young. J. Neuroph ysiol. 71:2446-2462, 1994; Spirou, G. A., and E. D. Young. ibid. 66: 1750-1 768, 1991) suggested that type IV units in decerebrate cat dorsal cochlear nucleus (DCN) are functional detectors of these spectral notches. Intracell ular marking studies by Ding et al. (Ding, J., T. E. Benson, and H. F. Voig t. J. Neurophysiol. 82:3434-3457, 1999) have shown that type III units in g erbil arise from the DCN's principal output neurons, which are thought to h ave type IV unit properties in cat. A relative paucity of type IV units in the decerebrate gerbil (Davis, K. A., J. Ding, T. E. Benson, and H. F. Voig t. J. Neurophysiol. 75: 1411-1431, 1996) has motivated this study of spectr al notch sensitivity in the gerbil DCN. Responses to notch noise stimuli we re recorded from 15 gerbil type III units to investigate whether these unit s may function as spectral notch detectors. For narrow notch noise stimuli, all 15 units showed excitatory responses. For progressively wider notches, the discharge rate of 13/15 units became inhibited. As the maximum limits of notch width were approached, 11/15 units showed some degree of recovery from this inhibition. This response pattern in gerbil type III units posses ses the salient features of notch noise responses in cat type IV units and implicates type III units in gerbilline spectral notch detection processes. (C) 2001 Biomedical Engineering Society.