Odour information processing in the mouse brain
The brain is a complex organ and though science has advanced in leaps and bounds, much of its workings remain a mystery. The ODORLEARNINGCIRCUIT (Sensory learning-induced changes of neuronal population activity in the olfactory bulb of awake mice) initiative studied how odourant information is processed from the OB to the specialised brain circuits in awake mice during various odour discrimination tasks. They employed two-photon microscopy to map neuronal population activity. OB contains two neuronal populations called mitral and tufted cells (MCs and TCs, respectively) that receive odour information and transmit it to the brain. Researchers used genetically encoded Ca2+ indicators (GECIs) to distinguish between the two neuronal populations in the OB. Study outcomes revealed state- and cell type-dependent ensemble plasticity in the OB with pattern separation of complex odour information through parallel sensory pathways. The MCs and TCs discriminated odours based on their concentration ranges. Intriguingly, ensemble odour discriminability remained stable over time though ensemble odour representation was constantly reorganised daily. The active odour discrimination learning tasks uncovered a hitherto unknown form of long-term ensemble plasticity exclusively in the MC population that improved odour discriminability. Collectively, the ODORLEARNINGCIRCUIT findings could be used to optimise information coding in the OB. Besides olfactory physiology, these methodologies could also be adapted to study the underlying mechanisms in other neural circuits.
