FEATURE-EXTRACTION BY BURST-LIKE SPIKE PATTERNS IN MULTIPLE SENSORY MAPS

In most sensory systems, higher order central neurons extract those st imulus features from the sensory periphery that are behaviorally relev ant (e.g., Marr, 1982; Heiligenberg, 1991). Recent studies have quanti fied the time-varying information carried by spike trains of sensory n eurons in various systems using stimulus estimation methods (Bialek et al., 1991; Wessel et al., 1996). Here, we address the question of how this information is transferred from the sensory neuron level to high er order neurons across multiple sensory maps by using the electrosens ory system in weakly electric fish as a model. To determine how electr ic field amplitude modulations are temporally encoded and processed at two subsequent stages of the amplitude coding pathway, we recorded th e responses of P-type afferents and E- and I-type pyramidal cells in t he electrosensory lateral line lobe (ELL) to random distortions of a m imic of the fish's own electric field. Cells in two of the three somat otopically organized ELL maps were studied (centromedial and lateral) (Mater, 1979; Carr and Mater 1986). Linear and second order nonlinear stimulus estimation methods indicated that in contrast to P-receptor a fferents, pyramidal cells did not reliably encode time-varying informa tion about any function of the stimulus obtained by linear filtering a nd half-wave rectification. Two pattern classifiers were applied to di scriminate stimulus waveforms preceding the occurrence or nonoccurrenc e of pyramidal cell spikes in response to the stimulus. These signal-d etection methods revealed that pyramidal cells reliably encoded the pr esence of upstrokes and downstrokes in random amplitude modulations by short bursts of spikes. Furthermore, among the different cell types i n the ELL, I-type pyramidal cells in the centromedial map performed a better pattern-recognition task than those in the lateral map and than E-type pyramidal cells in either map.