By Rich
Haridy
March 09, 2021
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The
neuroimaging study found our olfactory sense has a unique direct connection to
the hippocampus, unlike all other senses Photo credit:
nejron/Depositphotos
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The profound relationship between
memory and smell will be of no surprise to anyone. The way a certain odor can
conjure up a nostalgic reminiscence is unlike any other sense memory.
The unique nature of this
phenomenon is informally known as the Proust
Effect. Early in the 20th century, iconic French writer Marcel Proust penned
a classic series of stories titled In Search of Lost Time. One anecdote
described the way a vivid childhood memory was triggered by dipping a madeiline
cake into a cup of tea, and the idea of the Proust Effect was born.
Exactly how our olfactory system
seems to have the unique capacity to trigger emotional memories hasn’t been
clear. Observational and experimental research has over the years affirmed the
novel way smells can conjure memories. And neuroscientists have increasingly
understood that the human olfactory system has a direct connection with the
hippocampus.
This new research is the first to
rigorously compare functional pathways connecting different human sensory
systems with the hippocampus. The striking findings reveal our olfactory
pathways connect more strongly with the hippocampus than any other sense.
Christina Zelano, from the
Northwestern University Feinberg School of Medicine and lead investigator on the
project, suggests at some point in our distant history as our brains were
evolving, all other neural sense pathways were re-routed through different
regions of the brain. But for some reason our olfactory system retained a direct
connection with the hippocampus.
"During evolution, humans
experienced a profound expansion of the neocortex that re-organized access to
memory networks," explains Zelano. "Vision, hearing and touch all re-routed in
the brain as the neocortex expanded, connecting with the hippocampus through an
intermediary-association cortex-rather than directly. Our data suggests
olfaction did not undergo this re-routing, and instead retained direct access to
the hippocampus."
Alongside the fascinating
academic nature of the new findings, Zelano says this avenue of research
explicitly affirms the importance of olfactory experiences. Prior research has
found a strong bi-directional relationship
between olfaction and depression.
Patients suffering from anosmia,
a decreased sense of smell, are more likely to display signs of depression,
while conversely those suffering from depression often show reduced olfactory
performance. And, Zelano adds, considering anosmia
is a key symptom of COVID-19 there is an urgent need to understand how our
neural olfactory processes are linked to cognition, memory and well-being.
"The COVID-19 epidemic has
brought a renewed focus and urgency to olfactory research,” says Zelano. “While
our study doesn't address COVID smell loss directly, it does speak to an
important aspect of why olfaction is important to our lives: smells are a
profound part of memory, and odors connect us to especially important memories
in our lives, often connected to loved ones.”
The new study was published in
the journal Progress
in Neurobiology.
Source: Northwestern
University