Organization of temporal feature selectivity to whisker dynamics in the barrel cortex

MARAVALL R., M; MARTINI,F; MOLANO-MAZON, M; ALBARRACIN, AL

Congreso; 8th FENS Forum of Neurosciences; 2012

Neurons in the barrel cortex (BC) respond preferentially to a given whisker. However, BC neurons are sensitive to stimulus features beyond whisker identity, and this additional feature selectivity is essential to their function. For example, whisker-mediated tactile discrimination is thought to depend on the temporal pattern of whisker motion fluctuations evoked upon contacting an object. Neurons within the whisker pathway represent such fluctuations with high precision by virtue of their sensitivity to dynamical (temporally varying) stimulus features, e.g., velocity or acceleration. To understand BC sensory coding and functional architecture, it is essential to determine whether this feature selectivity is arranged systematically (e.g., into spatial maps). We performed juxtacellular and extracellular recordings in anesthetized rats and mice to characterize BC feature selectivity across preparations, and two-photon calcium imaging experiments in anesthetized mice to explore whether feature selectivity is spatially ordered across neural populations recorded within a ~350 micron cortical patch. Stimulation, applied with a piezoelectric wafer, consisted of different sequences designed to probe sensitivity to whisker position, velocity or acceleration. Stimuli were repeated at periodic and non-periodic intervals to detect tuning to a single interval (implying sensitivity to instantaneous frequency) or several intervals (implying integration over time). We found: (i) within each preparation, neurons displayed heterogeneous tuning; (ii) tuning to single intervals predominated, although some neurons integrated over relatively long timescales (~100 ms); (iii) tuning to whisker velocity predominated, although neurons were seldom purely tuned to velocity; (iv) no evidence for systematic spatial ordering of feature selectivity. These results indicate that neurons within a relatively small area of BC can represent diverse dynamical stimulus properties and timescales: feature selectivity varies on spatial scales finer than a barrel, consistent with a “salt-and-pepper” scheme. As a result, different neurons within a small region could provide a population signature of the stimulus.