Channelling CO₂ sensing

A single type of olfactory sensory neuron detects CO₂ in flies, but multiple second-order projection neurons (PNs) convey information about the stimulus intensity to higher brain centres. Lin et al. characterized the morphology and function of PNs innervating the ventral-glomerulus (PNvs) and found that two types of projection neurons, PNv-1 and PNv-2, were largely responsible for behavioural aversion to low (0.5%) and high (2%) concentrations of CO₂, respectively. By segregating input into a low- or a high-CO₂ pathway, the flies' perception of CO₂ can be modulated by intensity and, potentially, context.