Responses to tones and noise of single cells in dorsal cochlear nucleus of unanesthetized cats

Abstract

1. Single-unit responses in the dorsal cochlear nucleus of unanesthetized, decerebrate cats have been divided into two categoreis. These have been differentiated on the basis of responses to best-frequency tones. Type IV units responded to best-frequency tones with excitation from threshold to about 20 or 30 dB above threshold; at higher levels, their response was inhibitory. In a few cases, the excitatory area near threshold was not seen and in a few others, the response became excitatory again at high levels. Type IV units could be divided into two groups based on the length of time that inhibition was maintained in response to long tones. Type IV units are not seen in anesthetized cats. 2. Type II/III units responded to best-frequency tones of all levels with excitation. Nonmonotonic rate versus level functions were seen in type II/III units, but they were of much less drastic character; the discharge rate of nonmonotonic type II/III units was still well above spontaneous rate for tones 50 dB above threshold. Type II/III units defined in this way were found to have, on the average, lower rates of spontaneous activity and higher thresholds than type IV units. 3. Type II/III units responded weakly to broad-band noise in comparison to auditory nerve fibers and many of them did not respond at all to noise. Type IV units, with best frequencies above 0.9 kHz, gave excitatory responses to noise. 4. The inhibitory response areas of type IV units could be divided into two areas: a central inhibitory area in the vicinity of best frequency where on- and off-discharges and afterdischarges were seen; and inhibitory side bands at higher and lower frequencies where simple inhibitory responses were seen. In four units, it was possible to show that the central inhibitory area was converted to an excitatory area after administration of an anesthetic dose of pentobarbital. 5. Most type II/III and type IV units could be excited or inhibited by stimuli in the contralateral ear. Broad-band noise was a more effective contralateral stimulus than tones at the ipsilateral best frequency. 6. On the basis of the properties of type II/III and type IV cells, it is suggested that type II/III responses are recorded from interneurons which provide a large share of the inhibitory imput to type IV cells.

Limited Segregation of Different Types of Sound Localization Information among Classes of Units in the Inferior Colliculus

“…Sound localization cues are segregated, to some extent, in brainstem nuclei: DCN neurons respond to SNs but not to ITDs and only weakly to ILDs (Young and Brownell, 1976;Joris and Smith, 1998); MSO neurons respond to ITDs but weakly to ILDs (Goldberg and Brown, 1969); and LSO neurons respond strongly to ILDs but weakly to ITDs . Of course, neurons in both MSOs and LSOs should respond to SNs, like any tuned neuron.…”

Responses of Dorsal Cochlear Nucleus Neurons to Signals in the Presence of Modulated Maskers

“…Barbiturate anesthesia has been shown to strongly affect inhibition in the DCN (Evans and Nelson, 1973;Young and Brownell, 1976;Gdowski and Voigt, 1997). This is a potential confounding factor, because exploring the role of inhibition in CMR was the main objective of our study.…”

Age-Related Changes in the Inhibitory Response Properties of Dorsal Cochlear Nucleus Output Neurons: Role of Inhibitory Inputs

“…Vertical cells, termed narrow-band inhibitors, project strong nearcharacteristic frequency (CF) glycinergic inhibition onto fusiform cells (Caspary et al, 1987;Rhode, 1999;Davis and Young, 2000). This inhibition decreases tone-evoked activity in fusiform cells at higher intensities, resulting in flat or nonmonotonic CF rate-level functions (RLFs) termed type III/IV responses (Young and Brownell, 1976;Rhode and Smith, 1986). Nonmonotonic, near-CF rate-level responses are converted to more nearly monotonic functions by glycine receptor blockade (Caspary et al, 1987).…”