Scientists have already established a relatively strong connection between certain sensory inputs and their corresponding brain activity patterns [1]. With the use of devices like functional Magnetic Resonance Imaging (fMRI), they can directly measure electrical changes in the brain as a person is sensing or thinking about something [2]. While this is useful for identifying which parts of the brain are related to certain activities and evaluating new connections between areas of the brain, scientists have long struggled to identify which aspects of these patterns are important for perception. Since many features of brain patterns have been identified as redundant or ‘epiphenomenal’ [3], an understanding of the relative importance behind each aspect of these brain activity patterns would give us a valuable insight into the neurological mechanisms behind perception.
One area that scientists have explored this connection is in our perception of smell — primarily regarding how our brains process the electrical signals they receive from the olfactory bulb (the ‘hub’ of olfactory receptors). Scientists already understood that certain airborne molecules trigger receptors in the olfactory bulb, leading to a cascade of signals and eventually the sensation of smell; however, very little was previously known about how these complex patterns resulting from the airborne molecules actually contribute to our perception of odors [1].
Scientists at the NYU Grossman School of Medicine chose to explore this idea with genetically modified mice. The researchers in this study used mice that were engineered so that their brain cells could be activated by light (optogenetics), and then tested different patterns of stimuli to determine which aspects of the pattern most affected their perception of the odor. Because the olfactory receptors in the mice could be stimulated by light, scientists were essentially able to create ‘synthetic smells’ by designing their own patterns and timing of light-based stimuli. They trained the mice to pull a lever when exposed to one of these ‘synthetic smells’ and then systematically altered the pattern of stimuli to determine which alterations had the greatest impact on how well the mice could perceive the scent [3].
From this study, the scientists concluded that two main factors affect the perception of smell in mice: the type of receptor stimulated and the rhythmic timing of those stimuli. For example, they found that changes to cells stimulated earlier in the cascade of signals had a more significant effect on perception than cells stimulated later in the sequence. They used observations like this, in addition to a multitude of other data, to develop a computational framework that decoded the complex perceptual patterns of the mouse olfactory system. With this model, researchers can find direct links between brain activity and perception, advancing the capacity of scientists to develop technology aimed at manipulating perception [1].
Scientists already have a pretty good understanding of brain activity patterns and perception — but the connections between these concepts are still largely unknown. Decoding the pathways between neural activity and behavioral changes in mice is just one piece of this complicated puzzle.
References:
[1] Chong, E., Moroni, M., Wilson, C., Shoham, S., Panzeri, S., & Rinberg, D. (2020). Manipulating synthetic optogenetic odors reveals the coding logic of olfactory perception. Science, 368(6497), eaba2357. https://doi.org/10.1126/science.aba2357
[2] How do Scientists Study the Brain? (n.d.). Dana Foundation. Retrieved November 5, 2020, from https://www.dana.org/article/how-do-scientists-study-the-brain/
[3] NYU Langone Health / NYU School of Medicine. "Scientists decode how the brain senses smell." ScienceDaily. ScienceDaily, 18 June 2020. <www.sciencedaily.com/releases/2020/06/200618150304.htm>.