Burst firing is a neural code in an insect auditory system

TL;DR

This study demonstrates that burst firing in insect auditory neurons encodes sound stimulus features through spike count per burst, representing a sparse, non-firing-rate neural code that conveys significant information about sound transients.

Contribution

It reveals that burst activity in insect auditory neurons encodes stimulus features via spike count, influenced by stimulus dynamics, and contributes a quantitative analysis of this coding mechanism.

Findings

Burst probability is modulated by stimulus temporal features.

Spike count per burst encodes sound amplitude and duration.

Nearly half of the transmitted information is conveyed by burst activity.

Abstract

Various classes of neurons alternate between high-frequency discharges and silent intervals. This phenomenon is called burst firing. To analyze burst activity in an insect system, grasshopper auditory receptor neurons were recorded in vivo for several distinct stimulus types. The experimental data show that both burst probability and burst characteristics are strongly influenced by temporal modulations of the acoustic stimulus. The tendency to burst, hence, is not only determined by cell-intrinsic processes, but also by their interaction with the stimulus time course. We study this interaction quantitatively and observe that bursts containing a certain number of spikes occur shortly after stimulus deflections of specific intensity and duration. Our findings suggest a sparse neural code where information about the stimulus is represented by the number of spikes per burst, irrespective of the detailed interspike-interval structure within a burst. This compact representation cannot be interpreted as a firing-rate code. An information-theoretical analysis reveals that the number of spikes per burst reliably conveys information about the amplitude and duration of sound transients, whereas their time of occurrence is reflected by the burst onset time. The investigated neurons encode almost half of the total transmitted information in burst activity.