Summary. Though the things that surround us in the world seem immediate and real, we have a record of them only through the neuronal signals that they evoke in the cerebral cortex. One could almost say that we sense our cortical activity more directly than we sense the things encoded by that activity. The question of how cortical activity produces a sensation is among biology's oldest problems.

The present work, done in rats, is about the nature of the cortical representations underlying judgments of texture. The whisker sensory system in rats and mice is particularly intriguing because it is "active": the animal generates sensory signals by palpating objects through self-controlled whisker motion (just as we move our fingertips along surfaces to measure their tactile features). In our experiments, rats were trained to touch textures with their whiskers and to turn left or right for a reward according to the texture identity -- rough or smooth. Monitoring behavior with high-speed videography, we have found that on trials when the rat correctly identified the stimulus, the firing rate of cortical neurons in the time window a few hundred milliseconds before taking a decision varies according to the contacted texture - high for rough and lower for smooth. This firing rate code is reversed on error trials (higher for smooth than for rough). So when cortical neurons report the wrong stimulus the rat, "feeling" the signals of its cortical neurons, fails to identify the stimulus. In conclusion, firing rate in sensory cortex on each trial appears to lead directly to the animal's judgment of texture. This experiment begins to elucidate which features of cortical activity underlie the animal's tactile sensory discrimination capacity.



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(*) Dr. Mathew E. Diamond got his Ph.D. in Neurobiology in 1989 at the University of North Carolina in Chapel Hill, North Carolina USA. Presently, he is Director of the Laboratory of Tactile Perception and Learning, Cognitive Neuroscience Sector of the International School for Advanced Studies (SISSA) and is full Professor and Vice-coordinator of the Cognitive Neuroscience Sector. At the same time he is Visiting professor at the Institute for Theoretical Physics and Mathematics in Teheran. Previously he was he was Assistant Professor of theInstitute for Developmental Neuroscience Vanderbilt University in Nashville, Tennessee USA and Postdoctoral Research Associate at the Center for Neural Science in Brown University, USA.

Dr. Diamond has received many honors and prizes, amongst them I will highlight the New Horizons lecture in 2005 at the Indian Institute of Technology, Kharagpur. He has also received the Cortical Explorer Prize of the Cajal Club in 1994.

He is an Ad Hoc Reviewer in many journals of his field of expertise but also in Nature, Science and PNAS. He has lectured in many international meetings, and conferences both in Europe and the United States.) He is a co-author of the forthcoming book, a classic in the neurosciences: Nicholls JG, Martin AR, Wallace BG, Diamond ME, and Fuchs A (scheduled for 2009) "From Neuron to Brain, Fifth Edition," Sinauer, Sunderland MA. His publications are numerous in peer-reviewd journals as well as in book chapters.

Dr. Diamond is guiding a large number of postdocs, Ph.D, Master and undergraduate students and has taught extensively at Italian universities. He has collaborated with us at the ICTP in many activities, including the series of Borsellino Colleges in the neurosciences.