Why do certain smells bring back memories?

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Why do certain scents take you straight back to the past?

The nose can pick up thousands of different chemical signals, allowing us to detect millions of different smells. Some of those scents trigger powerful memories, and it’s all down to the wiring in our brains.

Incoming signals from the nose arrive at the olfactory bulbs before travelling on to the pyriform cortex. This part of the brain acts as a gateway, making connections to several other brain regions. There’s the orbitofrontal cortex, involved in decision-making; the amygdala, the brain’s emotional centre; the hypothalamus, which links the nervous and hormonal systems together; the insula, involved in consciousness; the entorhinal cortex, involved in memory and navigation; and the hippocampus, the master of long-term memory storage.

These connections help us to learn where smells come from and what they mean. Then, if we encounter the same smell again, we’ll instantly know how to respond. For example, the brain’s threat detection centre, the amygdala, lights up when we smell something that is unpleasant.

Smells can also trigger long-forgotten memories, often in vivid and emotional detail. These reach back into early childhood, and studies in rats suggest that they form during early development. Strong odour-linked memories may help animals to survive before their other senses are fully developed – as their eyes and ears improve, the need to remember smells becomes less important. Sensing the same scents again in adulthood can bring forgotten memories flooding back.

From nose to brain

Our sense of smell is wired into the memory and emotion centres of the brain

Image credit: Getty Images

Memory boost

The link between smell and memory has got scientists wondering whether we can use scents to improve our capacity to remember. Researchers at Northumbria University conducted studies to find out what happens to our brains when we sense powerful smells. In one study, they asked 180 volunteers to drink chamomile tea, peppermint tea, or plain hot water. Then they tested their mood and brain function. Compared to water, chamomile tea made volunteers less attentive, while peppermint tea improved their alertness.

In a separate study, 150 volunteers went into rooms that smelled of rosemary, lavender or nothing, and they were asked to complete a task at a particular time. Rosemary improved memory, but lavender made it worse, although the volunteers did feel calmer.

This article was originally published in How It Works issue 115, written by Laura Mears

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