One interesting observation is the emergence of receptive fields with bilaterally symmetric tuning (each direction and its opposite evoking similar responses) for high-frequency stimulation. This result is also in agreement with the electrophysiological data (1). Importantly, some of the grid designs used by the authors contain temporal correlations that, at high frequency, fall within the range of the neuronal integration time. Therefore motion in one direction is more likely to be followed by motion in the opposite direction, causing the neuronal tuning to look bilaterally symmetric. The authors note that, because of its fixed base, whisker movement is similarly constraint so that a movement in a certain direction is more probably followed by a resetting movement in the opposite direction. Because the authors were able to manipulate these properties of the stimulus (for example, removing any such correlation in a "random walk" grid) this work makes explicit the fact that the bilateral symmetry observed in Barrel cortex recordings can, to some extent reflect the temporal correlations in a high frequency stimulus rather than a genuine "wiring" of neurons with opposite directional selectivity. This work highlights the importance of considering how the choice of the sensory stimulus can significantly affect the estimation of the neuronal tuning curves.


Ehsan Arabzadeh & Justin Harris
School of Psychology
The University of Sydney
Australia

(1) Arabzadeh E, Zorzin E, Diamond ME. (2005) Neuronal encoding of texture in the whisker sensory pathway. PLoS Biol 3: e17. doi:10.1371/journal.pbio.0030017