Classification of unit types in the anteroventral cochlear nucleus: PST histograms and regularity analysis

Abstract

1. The responses of neurons in the anteroventral cochlear nucleus (AVCN) of barbiturate-anesthetized cats are characterized with regard to features of their responses to short tone bursts (STBs; 25 ms). A "decision tree" is presented to partition AVCN units on the basis of post-stimulus time histogram (PSTH) shape, first spike latency, and discharge rate and regularity calculated as functions of time during responses to STBs. The major classes of AVCN units (primary-like, primary-like-with-notch, chopper, and onset) have been described previously; in this paper, special attention is given to clarifying and systematizing boundaries between classes. Certain types of "unusual" units that may be confused with units in one of the major classes are also examined. 2. When STBs are presented synchronously (constant phase at onset), PSTHs of responses to very-low-frequency (less than 1.0 kHz) tones are difficult if not impossible to resolve into the classes listed above because all unit types phase-lock to low-frequency tones. However, when STBs are presented asynchronously, the responses of units with low best frequencies can be categorized on the basis of PSTH shape and first spike latency. 3. Primary-like, primary-like-with-notch, and onset units are distinguished primarily on the basis of PSTH shape. These three unit types have comparable minimum first spke latencies and synchronization to tones. One type of "unusual" response poses a particular hazard with respect to the generation of uncontaminated primary-like populations. Such "unusual" units have PSTHs that appear primary-like; these units are, however, distinguished by their unusually long first spike latencies. Unlike primary-like units, these "unusual" units show extremely poor synchronization to tones. 4. Chopper units are defined as having an initial response that is highly regular, resulting in the characteristic multimodal PSTH. "Unusual" units with multimodal PSTHs but whose initial responses are not highly regular (measured by the reproducibility of the initial firing pattern in response to multiple repetitions of a STB) are eliminated from the chopper populations. 5. In barbiturate-anesthetized cats, at least three patterns of chopper response can be distinguished on the basis of temporal patterns of rate and regularity adaptation. "Sustained" choppers show no adaptation of instantaneous rate (measured by the inverse of the mean interspike interval), and their discharge remains highly regular throughout the response. "Transiently adapting" choppers undergo a very rapid (less than 10 ms) decrease in instantaneous rate accompanied by a sharp increase in discharge irregularity.(ABSTRACT TRUNCATED AT 400 WORDS)

Response patterns to sound associated with labeled globular/bushy cells in cat

“…There is almost never any rate adaptation in OnL responses after the initial spike, as is typically observed in PL responses. Blackburn and Sachs (1989) described two OnL patterns: (1)PSTH had no notch, a well-timed onset spike and a sustained firing rate < 100 sp/s and (2) a PSTH that had a gradual notch (> 1.5 ms) to distinguish it from the PLn pattern. However, there is no single set of features that can be applied to distinguishing the two, as there is considerable overlap in steadystate firing rates, peak rates and spontaneous rates.…”

“…For example, Pfeiffer (1965) identified onset, primary-like and chopper responses in the ventral cochlear nucleus. Subsequently, PSTH response patterns have been greatly elaborated (Bourk, 1978;Blackburn and Sachs, 1989), and the relation of these PSTH patterns to the underlying morphology has been a subject of study. The introduction of intracellular labeling of physiologically characterized cells provided a firm basis for correlating physiological and morphological cell types (e.g., Rhode et al, 1983;Rouiller and Ryugo, 1984).…”

Statistical Analyses of Temporal Information in Auditory Brainstem Responses to Tones in Noise: Correlation Index and Spike-distance Metric

“…Neurons were classified into three response types based on Blackburn and Sachs (1989). Primarylike response types have irregular spike intervals and are associated with AVCN bushy cells (Cant and Morest 1979).…”

Localization of Click Trains and Speech by Cats: the Negative Level Effect

“…These issues may be reduced at higher auditory centers to counteract the negative level effect. For example, Blackburn and Sachs (1989) showed responses of a transient chopper in the ventral cochlear nucleus to long-duration tones (their Fig. 12).…”