Are the olfactory responses of patients in a coma or vegetative state signs of consciousness? (Yes)

Medical Xpress / Frontiers in Neuroscience ^ | May 31, 2023 | Ingrid Fadelli / Wanchun Wu et al

[ConservativeMind]

Severe head traumas in humans can lead to various stages of so-called disorders of consciousness (DoC). These are states in which consciousness is either partly or entirely absent, such as a coma; unresponsive wakefulness syndrome, also known as a vegetative state; and minimally conscious state.

Researchers recently carried out a study investigating the responses of patients in a coma or vegetative state to smells, to understand whether they could be used to evaluate consciousness.

As part of their study, the researchers evaluated the responses of 28 patients at different stages of DoC to olfactory stimuli. Out of these patients, 13 were in a vegetative state (UMS) and 15 in MCS. The study participants were divided into two groups based on whether they responded to olfactory stimuli or not.

"We recorded an olfactory task-related electroencephalogram (EEG) and analyzed the relative power and functional connectivity at the whole-brain level in the patients with DoC and healthy controls (HCs)," Wu wrote.

When Wu analyzed the data, they found that there was a relationship between the patients' olfactory responses and their levels of consciousness. They also found that patients in the no-olfactory responses group showed higher theta functional connectivity than patients in the olfactory response group after they were presented with the vanillin scent, and lower alpha and beta relative powers than healthy participants with no DoC.

The follow-up data collected three months later showed that 10 out of 16 of the patients who responded to olfactory stimuli during the study had recovered consciousness, while only 2 out of the 12 participants who did not respond to olfactory stimuli did. This suggests that a brain response to olfactory stimuli is typically a sign that patients with DoC are gradually recovering and regaining consciousness.

"Olfactory responses should be considered signs of consciousness," Wu explained.

[ConservativeMind]

This is another way to check on recovery in a comatose patient.

[ConservativeMind]

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[ryderann]

Vanillin scent? Probably have a higher rate of response to a hot, steaming all-the-way pizza...or maybe Cajun fried chicken.

[MayflowerMadam]

Really interesting. This “smell test” seems so logical that I wonder why it hadn’t been done in the past.

Put a doughnut under my nose, and I’m coming back!

Seriously, brain waves indicating a reaction to smells... very cool. I’ve heard that olfactory is supposed to be the strongest of the senses. I know for me, certain smells can zap me back 50 years in a heartbeat.

[Does so]

Mentos take me back to my Grandmother of 1952—61 years ago...!

[Scrambler Bob]

I’ve heard that olfactory is supposed to be the strongest of the senses.
= = =

Now consider that dogs’ sense of smell is 10K to 100K more than a human (many different numbers on that).

[MayflowerMadam]

Last summer at our Cousins’ Reunion, I hugged my cousin’s wife and, without thinking, I said, “Wind Song!”. I hadn’t had or smelled Wind Song since the ‘60s but recognized it immediately.

It zapped me back to another person and place that was bittersweet.

[Does so]

Dogs probably even have memory “flash-backs” when they greet their owners after long absenses.

We’ve seen their delightful reunions.

:)