Interneuron subtypes and Orientation Tuning

Abstract

arising from B. V. Atallah, W. Bruns, M. Carandini & M. Scanziani 73, 159-170 (2012); N. R. Wilson, C. A. Runyan, F. L. Wang & M. Sur 488, 343-348 10.1038/nature11347(2012); S.-H. Lee et al. 488, 379-383 10.1038/nature11312(2012)Parvalbumin-positive (PV(+)) and somatostatin-positive (SST(+)) interneurons are two principal subtypes of cortical GABAergic neurons that differ in morphology, physiological properties and postsynaptic targeting. Although GABAergic inhibition is known to be crucial for shaping orientation tuning in the visual cortex, it is unclear whether PV(+) and SST(+) interneurons have different roles. Recently, Atallah et al., Wilson et al. and Lee et al. addressed this issue by optogenetically manipulating each interneuron subtype, reaching different conclusions: some investigators found that SST(+) neuron activation sharpens orientation tuning, whereas PV(+) neuron activation has little effect, but others found that activation of PV(+) but not SST(+) interneurons sharpens orientation tuning. To understand the cause for the discrepancy we examined the impact of several experimental differences among the studies-anaesthesia and the level and duration of optogenetic stimulation-and found that the discrepancies can be largely explained by differences in the level and duration of interneuron activation.