In a study recently published in the journal Science Advances, Dr Nixon Abraham’s group from the Biology Department of IISER Pune showed in a mouse model that the nose can sense wind speed in addition to smells, and that chemical and mechanical inputs together constitute the olfactory (sense of smell) perception. The researchers stated that this is an important revelation on the current understanding of the sense of smell. “Our findings show that the olfactory system in the brain doesn’t just process chemical information from odours, but also integrates mechanical information from air movements inside the nasal cavity,” Dr Abraham, who led the study, said. “In essence, the nose acts as a dual sensor – one that can both smell and feel the air,” he added. Giving further context to the research question addressed in the paper, Dr Abraham said, “An anemometer measures the wind speed. In neuroscience, our understanding has traditionally emphasised the brain’s role in processing sensory information gathered through various sensors such as the eyes, nose, ears, skin, and proprioceptive receptors. While the brain integrates inputs from these sensory systems to form a cohesive perception of the environment, it has not been presumed to possess a specialised mechanism analogous to an anemometer for directly detecting and discriminating wind speed. Our findings present a fascinating possibility: the existence of a unique brain mechanism dedicated to sensing the wind speed, that of a biological anemometer.” Behavioural experiments Sarang Mahajan, who is the first author in the study, stated that as part of a series of behavioural experiments, mice were trained to distinguish between different airflows, wherein they could identify different airflows with an accuracy close to 90 per cent. When the team recorded brain activity using advanced techniques such as in vivo calcium imaging, genetic manipulations, and optogenetics, they found that specific inhibitory neurons in the olfactory bulb, the brain’s first relay station for smell, were critical for processing airflow information. When the activity of these inhibitory circuits was artificially increased or decreased, the ability of the mice to learn airflow-based tasks changed significantly. Strengthening the inhibitory signals slowed learning, while reducing inhibition made the animals learn faster. Interestingly, the same manipulations produced the opposite effects in odour-learning tasks. “This revealed that the brain uses different levels of inhibition to refine airflow and odour information. The olfactory bulb is essentially balancing two sensory streams, chemical and mechanical, to create a more complete perception of the world,” according to a statement released by IISER on Monday. Air helps enhance smell The researchers also found that when very faint odours were paired with air movements, the mice learned to recognise the odours much more quickly. This suggests that airflow cues enhance the brain’s ability to detect weak smells, allowing animals to better navigate their surroundings where odours are carried by varying airflows.
