Temporal features of spike trains in the moth antennal lobe revealed by a comparative time-frequency analysis

A novel method for quantifying similarities between oscillatory neural responses in wavelet time-frequency power profiles

Quantifying similarities and differences between neural response patterns is an important step in understanding neural coding in sensory systems. It is difficult, however, to compare the degree of similarity among transient oscillatory responses. We developed a novel method of wavelet correlation analysis for quantifying similarity between transient oscillatory responses, and tested the method with olfactory cortical responses. In the anterior piriform cortex (aPC), the largest area of the primary olfactory cortex, odors induce inhibitory activities followed by transient oscillatory local field potentials (osci-LFPs). Qualitatively, the resulting time courses of osci-LFPs for identical odors were modestly different. We then compared several methods for quantifying the similarity between osci-LFPs for identical or different odors. Using fast Fourier transform band-pass filters, a conventional method demonstrated high correlations of the 0-2Hz components for both identical and different odors. None of the conventional methods tested demonstrated a clear correlation between osci-LFPs. However, wavelet correlation analysis resolved a stimulus dependency of 2-45Hz osci-LFPs in the aPC output layer, and produced experience-dependent high correlations in the input layer between some of the identical or different odors. These results suggest that redundancy in the neural representation of sensory information may change in the aPC. This wavelet correlation analysis may be useful for quantifying the similarities of transient oscillatory neural responses.

Physiological organization and topographic mapping of the antennal olfactory sensory neurons in female hawkmoths, Manduca sexta

The hawkmoth, Manduca sexta, has been a keystone system for developmental, neurobiological, and ecological studies for several decades. Because many of its behaviors are driven by olfactory cues, a thorough understanding of the Manduca olfactory system is essential to studying its biology. With the aim of functionally characterizing single antennal olfactory sensory neurons (OSNs) and determining their detailed topographic location, we performed systematic single-sensillum recordings on 4 morphological types of olfactory sensilla: trichoid-A and -B and basiconic-A and -B. We were able to unambiguously differentiate the colocalized cells associated with single sensilla based on their spike amplitudes. Using a panel of 61 biologically relevant compounds established in behavioral and gas chromatography-electrophysiology experiments, we made 223 recordings from these sensilla. Based on the response spectra of 187 responding OSNs, the sensilla fell into 12 distinct functional classes encompassing 29 OSNs. Selectivity of the 25 responding OSNs varied from narrowly tuned (responding to only one or a subset of compounds), to very broadly tuned (responding to multiple compounds), in a concentration-dependent manner. Four OSNs, however, did not respond to the tested components. Topographic mapping of the sensilla revealed that some physiological sensillum types are confined to particular locations on the antennal surface while other classes are more or less irregularly scattered all over the antennal annuli. Such information will prove beneficial for future receptor deorphanization, in situ hybridization, and molecular manipulation experiments.