Biomechanical Texture Coding and Transmission of Texture Information in Rat Whiskers

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Dokumentart: PhDThesis
Date: 2019-08-02
Source: Nature Scientific Reports, volume 8, Article number: 11139 (2018)
Language: English
Faculty: 7 Mathematisch-Naturwissenschaftliche Fakultät
Department: Biologie
Advisor: Schwarz, Cornelius (Prof. Dr.)
Day of Oral Examination: 2019-07-23
DDC Classifikation: 570 - Life sciences; biology
Keywords: Haarkristall , Ratte , Codierung , Textur
Other Keywords:
Texture Coding in Rat Whiskers
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Classically, texture discrimination has been thought to be based on ‘global’ codes, i.e. frequency (signal analysis based on Fourier analysis) or intensity (signal analysis based on averaging), which both rely on integration of the vibrotactile signal across time and/or space. Recently, a novel ‘local’ coding scheme based on the waveform of frictional movements, discrete short- lasting kinematic events (i.e. stick-slip movements called slips) has been formulated. In the first part of my study I performed biomechanical measurements of relative movements of a rat vibrissa across sandpapers of different roughness. My major finding is that the classic global codes convey some information about texture identity but are consistently outperformed by the slip-based local code. Moreover, the slip code also surpasses the global ones in coding for active scanning parameters. This is remarkable as it suggests that the slip code would explicitly allow the whisking rat to optimize perception by selecting goal-specific scanning strategies. I therefore provide evidence that short stick-slip events may contribute to the perceptual mechanism by which rodent vibrissa code surface roughness. In the second part, I studied the biomechanics of how such events are transmitted from tip to follicle where mechano-transduction occurs. For this purpose, ultra-fast videography recording of the entire beam of a plucked rat whisker rubbing across sandpaper was employed. I found that slip events are conveyed almost instantly from tip to follicle while amplifying moments by a factor of about 1000. From these results, I argue that the mechanics of the whisker serve as a passive amplification device that faithfully represents stick-slip events to the neuronal receptors. Using measures of correlation, I moreover found that amongst the kinematic 8 variables, acceleration portrays dynamic variables (forces) best. The time series of acceleration at the base of the whisker provided a fair proxy to the time series of forces (dynamical variables) acting on the whisker base. Acceleration measurements (easily done via videography) may therefore provide an access to at least the relative amplitude of forces. This may be important for future work in behaving animals, where dynamical variables are notoriously difficult to measure.

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