Smell travels on superhighway to hippocampus in the brain
Northwestern University
This
new research suggests a neurobiological basis for privileged access by
olfaction to memory areas in the brain. The study compares connections between
primary sensory areas -- including visual, auditory, touch and smell -- and the
hippocampus. It found olfaction has the strongest connectivity. It's like a
superhighway from smell to the hippocampus.
"During evolution, humans experienced a profound expansion of the neocortex that re-organized access to memory networks," said lead investigator Christina Zelano, assistant professor of neurology at Northwestern University Feinberg School of Medicine.
"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."
The paper, "Human hippocampal connectivity is stronger in olfaction than other sensory systems" was published March 4 in the journal Progress in Neurobiology.
Epidemic
loss of smell in COVID-19 makes research more urgent In COVID-19, smell loss
has become epidemic, and understanding the way odors affect our brains --
memories, cognition and more -- is more important than ever, Zelano noted.
"There
is an urgent need to better understand the olfactory system in order to better
understand the reason for COVID-related smell loss, diagnose the severity of
the loss and to develop treatments," said first author Guangyu Zhou,
research assistant professor of neurology at Northwestern. "Our study is
an example of the basic research science that our understanding of smell, smell
loss and future treatments is built on."
Below
is a Q & A with Zelano about the importance of the sense of smell,
olfactory research and the link to COVID-19.
Why
do smells evoke such vivid memories?
"This
has been an enduring mystery of human experience. Nearly everyone has been
transported by a whiff of an odor to another time and place, an experience that
sights or sounds rarely evoke. Yet, we haven't known why. The study found the
offactory parts of the brain connect more strongly to the memory parts than
other senses. This is a major piece of the puzzle, a striking finding in
humans. We believe our results will help future research solve this mystery.'
How
does smell research relate to COVID-19?
"The COVID-19 epidemic has brought a renewed focus and urgency to olfactory research. 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 smell of fresh
chopped parsley may evoke a grandmother's cooking, or a whiff of a cigar may
evoke a grandfather's presence. Odors connect us to important memories that
transport us back to the presence of those people."
Loss
of smell linked to depression and poor quality of life
"Loss
of the sense of smell is underestimated in its impact. It has profound negative
effects of quality of life, and many people underestimate that until they
experience it. Smell loss is highly correlated with depression and poor quality
of life.
"Most
people who lose their smell to COVID regain it, but the time frame varies
widely, and some have had what appears to be permanent loss. Understanding
smell loss, in turn, requires research into the basic neural operations of this
under-studied sensory system.
"Research
like ours moves understanding of the olfactory parts of the brain forward, with
the goal of providing the foundation for translational work on, ultimately,
interventions."
This
was an international collaboration funded by The National Institute on Deafness
and Other Communication Disorders grants R01DC018539 and R01DC016364, Knut and
Alice Wallenberg Foundation and the Swedish Research Council.