Parallel Coding Schemes of Whisker Velocity in the Rat ’ s Somatosensory System 3 4 5

28 29 The function of rodents’ whisker somatosensory system is to transform tactile cues, in the form of 30 vibrissa vibrations, into neuronal responses. It is well established that rodents can detect numerous 31 tactile stimuli and tell them apart. However, the transformation of tactile stimuli obtained through 32 whisker movements to neuronal responses is not well-understood. Here we examine the role of 33 whisker velocity in tactile information transmission and its coding mechanisms. We show that in 34 anaesthetized rats, whisker velocity is related to the radial distance of the object contacted and its 35 own velocity. Whisker velocity is accurately and reliably coded in first-order neurons in parallel, by 36 both the relative time interval between velocity-independent first spike latency of rapidly adapting 37 neurons and velocity-dependent first spike latency of slowly adapting neurons. At the same time, 38 whisker velocity is also coded, though less robustly, by the firing rates of slowly adapting neurons. 39 Comparing firstand second-order neurons, we find similar decoding efficiencies for whisker 40 velocity using either temporal or rate-based methods. Both coding schemes are sufficiently robust 41 and hardly affected by neuronal noise. Our results suggest that whisker kinematic variables are 42 coded by two parallel coding schemes and are disseminated in a similar way through various 43 brainstem nuclei to multiple brain areas. 44 45