Fig 11. Schemes for demodulation of touch signals by vibrissa whisking signals.

(a) A scheme for a parallel pathway for the ex-afferent signal and a reafferent signal that encodes phase in the whisk cycle independent of touch to the vibrissae. The slope of the f-I curve is assumed to be modulated by the reafferent signal, as can occur if re-afference drives shunting inhibition. This scheme is relevant if the encoding of whisking by the skin and fur serves as the reafferent signal. (b) A scheme for a single pathway for both the ex-afferent signal, which encodes touch to the vibrissa, and re-afferent signal, which encodes phase in the whisk cycle, measured in terms of free whisking in air. The signals are mixed by a spike rate versus input current (f-I) function that has an accelerating slope. This scheme is relevant if both the ex-afferent and re-afferent input share the same ascending lemniscal input from VPM to layer 4 cortical neurons.