Neuronal processing of task-specific afferent whisker information in the rat barrel cortex
Final Report Abstract
The work done in the BaCoFun project helped to revolutionize our view how tactile perception works. Our hypothesis at the outset of the project was based on the classic notion that active touch (active whisking in our case) samples whisker vibrations directly and continuously reflecting the microscopic 3D texture probed by converting a spatial measurement of height/depth (the 3D texture) into a temporal signal (the vibrotactile signal). The idea has been called ‘intensive coding’ and was put forward by the Mountcastle and Lederman groups (LaMotte and Mountcastle, 1975). In this view the tactile system either integrates this vibrotactile interval to arrive at an ‘intensity code’ or analyzes spectral content to arrive at a ‘frequency code’. Our key perceptional experiments, conducted during both funding periods, accumulated strong evidence against intensive coding which led us to formulate an entirely new perceptional hypothesis for the epicritic tactile sense on the microscopic spatial scale. This new hypothesis is called ‘slip hypothesis’ and has been suggested by biomechanical observations of other workers in the field. We were the first to add evidence from combined measurement of neuronal activity and psychophysics. We elaborated critical predictions of the slip hypothesis. The most important one is that tactile perception should be based on ‘near-instantaneous’ signal processing, working like a wellknown class of machine learning algorithms called ‘change detection’. The slip hypothesis entails that microscopic texture information is carried in short lived, large amplitude kinematic events, whisker jerks, carrying information in a probabilistic, spatio-temporally discrete code, rather than in a continuous, small amplitude vibration corrupted by noise. In the second funding period, we published five full length reports supporting slip coding and perception. We worked intensively on the motor side of the problem publishing three full length papers and summarized the new hypothesis in three review articles covering the perceptual processes and motor behavior. In a fourth review we integrated our results with those of the BaCoFun partners to showcase our view on how the respective neuronal coding is implemented in the barrel column. Conceptually, our work may have far reaching impact also on our understanding of tactile processing of ridge associated signals in primate glabrous skin. A new DFG funded project, inspired by this work, has started recently to study the concept of near-instantaneous coding also in humans.
Publications
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(2013) Barrel cortex function. Progress in Neurobiology 103: 3–27
Feldmeyer, D., Brecht, M., Helmchen, F., Petersen, C.C.H., Poulet, J., Staiger, J., Luhmann, H., Schwarz C.
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(2013) Beyond GLMs: A generative mixture modeling approach to neural system identification. PLOS Comp. Biol., 9:e1003356
Theis, L., Chagas, A.M. Arnstein, D., Schwarz, C., Bethge, M.
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(2013) Functional analysis of ultra high information rates conveyed by rat vibrissal primary afferents. Front Neural Circuits 7:190
Chagas, A.M.; Theis, L., Sengupta, B., Stüttgen, M.C., Bethge, M., Schwarz, C.
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(2013) Rhythmic whisking area (RW) in rat primary motor cortex: an internal monitor of movement-related signals? J Neurosci 33:14193–14204
Gerdjikov T.V., Haiss F., Rodriguez-Sierra O., Schwarz C.
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(2014) Are spatial frequency cues used for whisker-based active discrimination? Front. Behav Neurosci 8:379
Georgieva, P., Brugger, D. and Schwarz, C.
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(2014) Studying motor cortex function using the rodent vibrissal system. e-Neuroforum 5:20-27
Chakrabarti, S., Schwarz, C.
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(2015) Corticofugal projection patterns of whisker sensorimotor cortex to the sensory trigeminal nuclei. Front Neural Circuits 9:53
Smith, J.B., Watson, G.D., Alloway, K., Schwarz, C.,Chakrabarti S.
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(2015) Support for the slip hypothesis from whisker-related tactile perception of rats in a noisy environment. Front Integr Neurosci. 9:53
Waiblinger, C., Brugger, D., Whitmire, C.J., Stanley, G.B., Schwarz C.
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(2015) Vibrotactile discrimination in the rat whisker system is based on neuronal coding of instantaneous kinematic cues. Cereb Cortex 25:1093–1106
Waiblinger, C., Brugger, D., Schwarz C.
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(2015) Whisking control by motor cortex., Scholarpedia, 10(3):7466
Schwarz, C., Chakrabarti, S.
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(2016) The slip hypothesis: Tactile perception and its neuronal bases. Trends Neurosci 39:449–462
Schwarz C.
