Biomedical subjects

Stefano Panzeri

Publications and source records attributed to Stefano Panzeri.

5 recordsLinked to original sources

PubMed2003

Correlations, feature-binding and population coding in primary visual cortex.

To test the hypothesis that correlated neuronal activity serves as the neuronal code for visual feature binding, we applied information theory techniques to multiunit activity recorded from pairs of V1 recording sites in anaesthetised cats while presenting either single or separate bar stimuli. We quantified the roles of firing rates of individual channels and of cross-correlations between recording sites in encoding of visual information. Between 89 and 96% of the information was carried by firing rates; correlations contributed 4-11% extra information. The distribution across the population of either correlation strength or correlation information did not co-vary systematically with changes in perception predicted by Gestalt psychology. These results suggest that firing rates, rather than correlations, are the main element of the population code for feature binding in primary visual cortex.

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PubMed2003

Decoding neuronal population activity in rat somatosensory cortex: role of columnar organization.

The present study asks in what way the activity of a neuronal population responding to a sensory stimulus could be most efficiently decoded, or 'read off', by the target neurons. A simple solution to this problem has been proposed - pooling the activity of responding neurons. However, pooling can be inefficient if sensory information is encoded by the 'label' of each neuron firing a spike. We have tested the efficiency of pooling by quantifying the extent to which information about a sensory stimulus is diminished when the identity of the individual neurons is lost by pooling. Analyzing the response of small groups of neurons in rat barrel cortex to single-whisker deflection, we found that pooling neurons within the same column is efficient for representing stimulus position; it causes a loss of only 1% of the information about whether the principal whisker was stimulated, and a loss of 5-12% of the finer information about which of nine possible whiskers (the principal and its neighbors) was stimulated. Cross-column pooling led to larger information losses, in the range of 25-55%. Thus, to decode stimulus position from the discharge of barrel cortex populations, 'downstream' neurons could pool the activity arising from neurons of the same column, while maintaining the activity arising from neurons of separate columns at least partially segregated. Since such parcellation is present in some of the projections from barrel cortex, these findings suggest that columnar organization of barrel cortex serves to facilitate decoding of the location of the stimulated whisker.

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PubMed2002

Population coding in somatosensory cortex.

Computational analyses have begun to elucidate which components of somatosensory cortical population activity may encode basic stimulus features. Recent results from rat barrel cortex suggest that the essence of this code is not synergistic spike patterns, but rather the precise timing of single neuron's first post-stimulus spikes. This may form the basis for a fast, robust population code.

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PubMedDate not supplied

A critical assessment of different measures of the information carried by correlated neuronal firing.

Information theoretic measures have been proposed as a quantitative framework to clarify the role of correlated neuronal activity in the brain. In this paper we review some recent methods that allow precise assessments of the role of correlation in stimulus coding and decoding by the nervous system. We present new results that make explicit links between types of encoding and decoding mechanisms based on correlations. We illustrate the concepts by showing that the spike trains of pairs of neurons in rat somatosensory cortex can be decoded almost perfectly without including knowledge of correlation in the read-out model, although in this neural system correlations between spike times contribute appreciably to stimulus encoding.

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PubMedDate not supplied

The role of individual spikes and spike patterns in population coding of stimulus location in rat somatosensory cortex.

This report addresses the nature of population coding in sensory cortex by applying information theoretic analysis to data recorded simultaneously from neuron pairs located in primary somatosensory cortex of anaesthetised rats. We studied how cortical spike trains code for the location of a whisker stimulus on the rat's snout. We found that substantially more information was conveyed by 10 ms precision spike timing compared with that conveyed by the number of spikes counted over a 40 ms response interval. Most of this information was accounted for by the timing of individual spikes. In particular, it was the first post-stimulus spikes that were crucial. Spike patterns within individual cells played a smaller role; spike patterns across cells were negligible. This pattern of results was robust both to the exact nature of the stimulus set and to the precision at which spikes were binned.

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