Sorry for the morbid question.
September 23, 2011 8:43 AM   Subscribe

Hospice and palliative-care providers often tell patients' families and friends that as people die, hearing is the last sense to go. Is there any science behind the claim?

The idea that hearing is the last sense to go as a person dies seems kind of fishy to me. I know that it's generally offered as a comfort to the soon-to-be bereaved, enabling them to speak their feelings, and to have some sense of communication and closure. Which is a good thing.

That said, I was wondering if neuroscience has a general understanding of how the brain shuts down during end-stage terminal illness, in terms of localized brain death. Are there similarities in the course of brain death across patient groups? Are some cortices or gyri likely to be affected sooner than others? Is "hearing goes last" referring to auditory brainstem response? Something else?
posted by evidenceofabsence to Science & Nature (10 answers total) 6 users marked this as a favorite
I don't know if this question is susceptible to being studied by means available to neuroscience. What I mean is that getting a good answer would require one of two things: getting brain imaging data of someone close to death (fraught with ethical complications), or developing animal models of end-stage terminal illnesses. And we all remember how that FPP about cat research went.

We do know that the retina is very sensitive to blood oxygenation levels. You can get visual distortions ("seeing stars") by standing up too fast, but it typically doesn't affect hearing as much… Although, on second thought, people who get vasovagal syncope do sometimes report tinnitus prior to an episode.

Ultimately, this is all happening in the brain, and the brain is very hungry for oxygen. And although parts of the brain are specialized for different functions, it's all basically composed of the same tissue, and consumes oxygen at roughly the same rate.

My tentative guess is that the "hearing goes last" thing is a well-intentioned set phrase for comforting visitors. It might be "inspired by fact" in some way, but it doesn't actually mean much. If the individual is conscious, they can probably see and hear you. If the individual is unconscious, then they definitely can't see you, and talking at them can't hurt.
posted by Nomyte at 9:20 AM on September 23, 2011 [2 favorites]

My mother, who works in hospice care and is a clinician, had this to say:

"What I find is a lot of anecdotal findings. I don’t have enough of a neuro background to expound on this. I do know that as the body starts to die and shut down, the neocortex shuts down first. That’s the part of your brain that is in charge of thoughts and memories. Then the brain stem shuts down. This controls our automatic physical responses – breathing, blood pressure, heartbeat, temperature control, etc. Hearing is part of our brain stem’s job. It’s hard to ask someone if they can hear you when the neocortex has shut down, because they can’t respond. That part of their brain is dysfunctional. But the brain stem is still working, so we assume that hearing is still intact. They may not be able to process those thoughts, since higher function tasks are no longer taking place. There's also research based on electroencephalograms (EEGs) of people's brain waves that indicates hearing is the last sense to go.

Hope this is of some help."
posted by juniperesque at 10:51 AM on September 23, 2011 [7 favorites]

I wonder if some evidence for this can be gleaned from the fact that people can sometimes hear and remember conversations that take place around them when they're unconscious. You can't see then and may or may be able to feel, but sometimes you're apparently able to hear.
posted by WorkingMyWayHome at 10:52 AM on September 23, 2011

I've passed out from heat exhaustion before, and I can confirm WMWH's comment above. My sight and balance/coordination faded away, but I could clearly hear things around me just before it happened.

It's not the same as death, obviously, but hearing does seem to function a bit longer than other senses as unconciousness strikes.
posted by jdwhite at 11:06 AM on September 23, 2011

That's supposed to make someone feel better? "Your loved one is trapped inside a dead body and can still hear us talking"? Ugh, I hope they give that up by the time I would be the intended recipient of such "comfort".

Well, you can tell if someone can't see you. Their eyes don't focus on you. With hearing, if the person can't talk or move really, you can't tell for sure if they can hear or not, because our ears don't really perk and swivel like a dog's or something to indicate we are hearing.
posted by sweetkid at 11:10 AM on September 23, 2011

They might still have some kind of automatic response to a loud noise if they can still hear it when a siren goes by.
posted by jenfullmoon at 1:10 PM on September 23, 2011

Caregivers and techs are given the same information so they don't distress or disrespect the patient, so that's another layer to investigate.
posted by batmonkey at 2:28 PM on September 23, 2011

Yeah, even if the evidence for it isn't that strong, you want people to err on the side of caution here, just in case Grandpa can still hear them.

This conversation is also reminding me of a coworker years ago who had some sort of episode due to a neurological issue; I remember him telling me after he'd recovered that he fell down and couldn't speak, see, or move, but he could still hear people talking around him.
posted by WorkingMyWayHome at 6:20 PM on September 23, 2011

More anecdata: when my mother was dying, she was no longer able to speak or even open her eyes, but I would sing to her and she would make a humming sound so I think that she was still hearing.
posted by a humble nudibranch at 7:44 PM on September 23, 2011

I used to teach sensation and perception as part of my psychology courses, but I'm not a neuroscientist so this could be not entirely correct. However, I'll give it a shot:

Hearing is a bit of a different process than other senses, because in a way, it's more mechanical. Taste and smell are what are traditionally referred to as the chemical senses, because they depend on receptors in the tongue and olfactory bulbs being stimulated by chemicals that fit into specific receptor sites. Sight and touch depend on nerve stimulation--you touch something with your fingertips and that stimulates receptors that are sensitive to pressure, hot and cold, etc. An image falls on your retina and stimulates rods and cones in certain areas and that in turn stimulates your optic nerve. Once the nerves are no longer working (as in death), those messages received by your tongue, olfactory bulbs, fingertips and retinas don't really have anywhere to go, if they are received at all.

Hearing is kind of different, because it's a Rube Goldberg-esque series of vibrations set off by sound waves, and there's a relatively long chain reaction that happens before the auditory nerve is stimulated and the ultimate message is sent to the brain. First, the sound goes in through the auditory canal, sets the eardrum vibrating, and this, in turn, vibrates the auditory ossicles (the small bones in your ear, known as the hammer, anvil, and stirrup) which then vibrates the oval window, a small membrane that covers an opening to the inner ear. Inside the inner ear, the fluid inside the cochlea vibrates, vibrating the basilar membrane, causing the organ of Corti (which contains the hair cells that combine to form the auditory nerve) to move up and down and rub up against another membrane, which stimulates the hair cells and ultimately sends messages to the brain.

That's a lot that happens in between the sound wave entering our ear and the auditory nerve being stimulated, and I suspect that most of that can happen immediately after death. After a while things decay and it might not work so well, but within a few minutes of the brain shutting down and being unable to receive messages from sensory receptors, the eardrum, auditory ossicles, and cochlea could very well still function and be stimulated by sound waves, even if the message stops once it gets to the (now disconnected, in a way) auditory nerve. This might be why there's the belief that hearing is the last sense to go--the mechanics still work for a while, even if perception by the brain doesn't happen.

tl;dr: lots of the structures in your ear could still be functional after death, even if your nervous system isn't functioning anymore.
posted by Fuego at 10:14 PM on September 24, 2011

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