Regulation of burst dynamics improves differential encoding of stimulus frequency by spike train segregation

Distinguishing between different signals conveyed in a single sensory modality presents a significant problem for sensory processing. The weakly electric fish Apteronotus leptorhynchus use electrosensory information to encode both low-frequency signals associated with environmental and prey signals and high-frequency communication signals between conspecifics. We identify a mechanism whereby the GABA(B) component of a feedback pathway to the electrosensory lobe is recruited to regulate the intrinsic burst dynamics and coding properties of pyramidal cells for these behaviorally relevant input signals. Through recordings in an in vitro slice preparation and a reduced model of pyramidal cells, we show that recruitment of dendritic GABA(B) currents can shift the timing of a backpropagating spike and its influence on an intrinsic burst mechanism. This regulation of burst firing alters the coding properties of pyramidal cells by improving the correlation of burst and tonic spikes with respect to low- or high-frequency components of complex stimuli. GABA(B) modulation of spike backpropagation thus improves the segregation of burst and tonic spikes evoked by simulated sensory input, allowing pyramidal cells to parcel the spike train into coding streams for the low- and high-frequency components. As the feedback pathway is predicted to be activated in circumstances where environmental and communication stimuli coexist, these data reveal a novel means by which inhibitory input can regulate spike backpropagation to improve signal segregation.