Encoding and processing of sensory information in neuronal spike trains

Recently, a statistical signal-processing technique has allowed the informa tion carried by single spike trains of sensory neurons on time-varying stim uli to be characterized quantitatively in a variety of preparations. In wea kly electric fish, its application to first-order sensory neurons encoding electric field amplitude (P-receptor afferents) showed that they convey acc urate information on temporal modulations in a behaviorally relevant freque ncy range (<80Hz). At the next stage of the electrosensory pathway (the ele ctrosensory lateral line lobe, ELL), the information sampled by first-order neurons is used to extract upstrokes and downstrokes in the amplitude modu lation waveform. By using signal-detection techniques, we determined that t hese temporal features are explicitly represented by short spike bursts of second-order neurons (ELL pyramidal cells). Our results suggest that the bi ophysical mechanism underlying this computation is of dendritic origin, We also investigated the accuracy with which upstrokes and downstrokes are enc oded across two of the three somatotopic body maps of the ELL (centromedial and lateral), Pyramidal cells of the centromedial map, in particular I-cel ls, encode up- and downstrokes more reliably than those of the lateral map. This result correlates well with the significance of these temporal featur es for a particular behavior (the jamming avoidance response) as assessed b y lesion experiments of the centromedial map.