Distributed neuronal coding with first spikes timing in the somatosensory system

Untangling the neural code underlying sensory perception
requires the mapping of physical stimulus parameters to
neuronal responses. The speed by which rodents discriminate between tactile stimuli and neuronal response reliability in the somatosensory system suggest that temporal
coding might be used to encode sensory stimuli. We show
that the relative timing of the first impulses in an ensemble
of first-order neurons accurately and reliably conveys
whisker velocity. Stimulus onset time can be assessed using
stimulus-independent response latency of rapidly adapting
neurons, while stimulus identity can be estimated by
stimulus-dependent first spike latency of slowly adapting
neurons. Velocity coding by relative spike timing is robust,
and not affected by neuronal noise. We show that these two
aspects of neuronal responses are disseminated through
different functional pathways to the rest of the brain and
allow first-order neurons to rapidly and reliably transmit
tactile information with the very first spikes emitted by
neuronal population.