Laminar specific encoding of texture elements in rat barrel cortex

Abstract

Texture discrimination by rats is exquisitely guided by fine-grain mechanical stick-slip motions of the face whiskers as they encounter, stick to, and slip past successive texture-defining surface features like bumps and grooves. Neural encoding of successive stick-slip texture events will be shaped by adaptation, common to all sensory systems, whereby receptor and neural responses to a stimulus are affected by responses to preceding stimuli, allowing resetting to signal novel information. Additionally, when a whisker is actively moved to contact and brush over surfaces, that motion itself generates neural responses that could cause adaptation of responses to subsequent stick-slip events. Nothing is known about encoding in the rat whisker system of stick-slip events defining textures of different grain or the influence of adaptation from whisker protraction or successive texture-defining stick-slip events. Here we recorded responses from Halothane anaesthetised rats in response to texture defining stimuli applied to passive whiskers. We now demonstrate that, across the columnar network of the whisker-recipient barrel cortex, that adaptation in response to repetitive stick-slip events is strongest in uppermost layers and equally lower thereafter; that neither whisker protraction speed or stick-slip frequency impede encoding of stick-slip events at rates to 34.08 Hz; and that layer 2 normalizes responses to whisker protraction to resist effects on texture signalling. Thus, within laminar-specific response patterns, barrel cortex reliably encodes texture-defining elements even to high frequencies.

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