MadSci Network: Neuroscience |
Here is an answer to your question, courtesy of my colleague Dr. Roger Remington. There are strong connections between the parts of the brain that process smell (rhinencephalon) and emotion (limbic system), with weaker connections between rhinencephalon and more cognitive parts of the brain (cortex). That is likely why smells can be recognized as familiar with strong emotional attachments even when we can't recall the names or situations in which we smelled those things before. This only answers part of the question: why we observe the phenomena. The deeper question is why the brain should be wired this way. I speculate that this has to do with our evolution from smell-dominant ancient ancestors. In early mammals smell was the dominant sense and it remains so today. Smell was a crucial sense, along with hearing, that determined whether something should be eaten, fled from, mated with, attacked, or ignored. Emotional responses of desire, fear, aggression, and such are important motivators for these actions. Such emotional responses continue to provide strong incentives for our behavior to this day. The emergence of vision as our dominant sense modality coincided with an expansion of the neocortex, the area of the brain that controls our rational thought. The pattern of impulsive stimulus-response behavior that characterized earlier mammals was replaced by a system that weighed our actions against a range of outcomes in a more deliberate way (not completely deliberate, but more so.) The rhinencephalon was not a part of this expanded deliberative cortical development, instead retaining its close connection with subcortical centers for emotional control (limbic system).
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