Daniel Shulz – February 22, 2013
Daniel Shulz, CNRS UPR-3293 Equipe Traitement Sensoriel, Neuromodulation et Plasticité, Gif sur Yvette : « Neuronal representation of complex tactile scenes ».
Friday, February 22, 2013 at 11:30 am
The tactile system is unique among the other sensory systems in that it must convey information about objects that come directly in contact with the receptors on the skin surface. These objects must be represented in the central nervous system accurately in space and rapidly in time so as to produce optimized exploratory strategies. Different animal species have adapted to this requirement by the use of distinct parts of the body to gather tactile information. While primates reach and feel objects mainly with their fingers many other mammals, particularly rodents, use the whiskers on the snout for exploring the environment. The temporal structure of whisker deflections and the temporal correlation between deflections occurring on several whiskers simultaneously vary for different tactile substrates. To explore the neural basis of the haptic sense, we use, as a system model, the primary somatosensory cortex of the rat, which receives information from the whiskers. We hypothesize that tactile discrimination capabilities rely strongly on the ability of the system to encode different levels of inter-whisker correlations.
To test this hypothesis, we generate complex spatio-temporal patterns of whisker deflections during electrophysiological recordings in the barrel cortex, the ventro-posterior medial (VPM) nucleus of the thalamus and the trigeminal ganglion. A piezoelectric-based stimulator featuring 24 independent and fully adjustable whisker actuators was built for this purpose (Jacob et al., 2010). Using this stimulator in anesthetized rats, we showed that cortical and thalamic neurons exhibit direction selectivity to the apparent motion of a multivibrissal stimulus (i.e. an emerging property of the global stimulus), uncorrelated to the local direction of individual whiskers (Jacob et al. 2008, Neuron; Ego-Stengel et al., 2012, J. Neurosci.) Finally, we applied a reverse correlation approach to this problem by using Gaussian white noise stimulation on 24 whiskers and progressively varying the level of temporal correlation among them. Based on spike-triggered analysis for various levels of inter-whisker
correlation, our recent findings (Estebanez et al., 2012, Nat. Neurosci) show that neuronal cortical networks implement coexisting coding schemes to cope with the varying statistics of the tactile sensory world.
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