Divergence alone cannot guarantee stable sparse activity patterns if connections are dense
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KeywordsInput Pattern Olfactory System Sparse Code Mushroom Body Antennal Lobe
It is quite well known, and we have recently confirmed it for the olfactory system in insects , that sparse activity is necessary for efficient pattern recognition and memory formation. In many brain centers, including the olfactory system, strongly divergent connections with high-threshold post-synaptic neurons are believed to generate these sparse patterns. We have shown in a generic model that this interpretation rests on the assumptions that the connections are not only divergent but also sparse. However, in locusts the connections from the antennal lobe to the mushroom bodies have been found to be not sparse. To the contrary, experimental observations seem to imply connectivities with 50% of all-to-all connections . Our generic model elucidates how such dense connections lead to instabilities with respect to noise and fluctuations in the incoming signals. We then suggest a hypothesis how the original coding idea can be rescued by appropriate feed-forward gain control mechanisms.
TN acknowledges helpful discussions with Falk Hildebrand. This work was partially funded by the Biotechnology and Biological Sciences Research Council (grant number BB/F005113/1).
This article is published under license to BioMed Central Ltd.