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Stefano Panzeri

 

Wednesday 24th September 2014

Time: 4pm

 

Basement Seminar Room

Alexandra House, 17 Queen Square, London, WC1N 3AR

 

On the contribution of spike counts and millisecond-scale spike patterns to somatosensory coding and perception

 

In generating a percept and selecting an action based on that percept, does the brain use the simple code of spike counts on a tens of millisecond scale, or a more complex code based on the relative temporal displacement of action potentials on a millisecond-scale (a “pure temporal code”), or a combination of both? To investigate this question, we recorded responses from neurons in primary (S1) and secondary (S2) somatosensory cortex as five rats performed a tactile discrimination. On each trial the rat was presented one of three textures and used its whiskers to palpate the stimulus; it was required to withdraw and turn to the reward spout specified by texture identity. We computed two types of information carried by spike count, by a pure temporal code, and by the combination of both during each whisker’s contact with the texture: the information carried about texture in trials where the rat made a correct choice, and the information carried about the animal’s behavioral choice. For both types of information, the S1 and S2 neurons’ pure temporal code carried more information than spike count, and their combination carried much more texture information than each code alone. This suggests that the neural code used by somatosensory cortical neurons to encode information and its readout mechanism used to produce behavior rely on a multiple-time-scale combination of millisecond firing patterns and of spike counts. This leads to the hypothesis that single-trial texture information in millisecond precise relative time of spikes had a direct impact on the accuracy of the rat’s percept that goes beyond what provided by spike counts. We confirmed this hypothesis by finding that the rat’s choice was more likely to be correct when the relative temporal displacement of spikes in that trial carried faithful texture information, and choice was less likely to be correct when this purely temporal code carried misleading texture information. The association between behavioral performance and rate was significant too, but much less strong than that of spike timing. These results indicate that the temporal pattern of firing of cortical neurons, not just their time-averaged activity, contributes to somatosensory perception.

This is joint work between the Neural Computational laboratory at IIT and the Tactile Perception Laboratory at SISSA

 

Stefano Panzeri is a computational neuroscientist currently working as Research Professor at the Italian Institute of Technology in Rovereto, Italy. He did his PhD at SISSA (Trieste) under the supervision of Alessandro Treves. He then worked as Postdoc at the University of Oxford, as an MRC Research Fellow at the University of Newcastle, as a Reader at University of Manchester, and as Professor at the University of Glasgow.  His research focuses on how network os neurons in the cerebral cortex encode and transmit sensory information.