I’ve spent a couple of decades reading about meat computers and I often think about where X human behavior fits best in the meat hardware. One of these bits of behavior is the very existence of things like contagious feelings, abstract feelings, cooties, bad words, profanity, vulgarity and similar.

In fact it seems inevitable that someone with tourette’s syndrome and a habitat of reading brain science would get here. Like I mentioned in the last post I don’t have that sensitivity. It was always what other people were sensitive to, and watching that very carefully, like an instinct. I think I found some things that get to this part of language via the olfactory system of all things, and a bunch of other things too. Bear with me, it’ll take some setup.

The senses and olfactory systems.

There are more than 5 senses but I’m sticking with the 5 traditional senses here. Every time we have a reaction to something we sense (think of a mosquito on your arm) that data gets processed into an object, sent to the thalamus, and then sent to the amygdala. Unless it’s the sense of smell. Olfaction is different. Olfaction gets priority access to the amygdala. This I think is related to smell as the oldest sense.

Here is a figure of the first sets of connections involving olfaction in the mouse. And most amphibians, reptiles and mammals. It’s that old, back to jawless vertebrates. I’ll be coming back to it. I adapted a figure from the following paper.

Subpopulations of Projection Neurons in the Olfactory Bulb. Imamura 2020

It’s a very ancient system. It’s also ancestrally a DUAL olfactory system. The olfactory epithelium (OE) and the main olfactory system (MOS) is one part (the green connections), and the vomeronasal organ (VNO) and the accessory olfactory system (AOS) is the other part (the red connections). You may have heard about humans and pheromone detection, if it were a thing, that’s the VNO. The VNO is a fluid pump for sampling of non-volitile substances that the OR can’t as easily sample through diffusion in air. Like hormones/pheromones, big, often non-polar molecules. Along with regular sniffing of orifices, faces and bodies in our ancestors.

The olfactory epithelium (OE) does smell in general, the VMO does non-volatile smell related to other beings including ones own kind. I’m emphasizing this because in a minority of creatures with olfactory systems, including humans, the accessory olfactory system is GONE.

The human vestigial accessory olfactory system.

We have a rudimentary VMO, there is a tiny remnant accessory olfactory nerve, and no accessory olfactory bulb (AOB). Our accessory olfactory genes are full of lots of pseudogenes (broken, mutated and not expressed). All of the vomeronasal receptors but 5 are pseudogenes, and those 5 are in the OE, not the VMO. The genomic basis of vomeronasal-mediated behaviour. Ibarra-Soria 2013

With that knowledge, one day while reading about the various behaviors the AOS seems to be able to manipulate I had a thought…what about the meat computer hardware just downstream from the AOB? Humans still have that! It occurred to me that these systems could be like feelings and behaviors cut off from olfactory control. A source of abstracted feelings and behaviors that we can use in language like abstract, non-literal language. Reminiscent of “phantom limbs” but much older.

Here’s the passage from the paper that stood out to me and gave me the thought.

“…pheromones are substances that are secreted by one individual and received by a second individual of the same species, in which they release a specific reaction, for example, a definite behavior or a developmental process” (Karlson and Lüscher 1959). Although this definition properly applies to many insect chemostimuli, it often falls short when applied to mammalian social chemosignals. Indeed, this issue has sparked some intense debate in the past (Doty 2010; Wyatt 2014).

Today, it is clear that the VNO is not exclusively dedicated to “pheromone detection.” For one, the VNO is critical for detection of predator odors, which are formally distinct from pheromones, and rather defined as “kairomones” (see below). Similarly, in snakes the VNO is important for prey detection (Halpern and Frumin 1979). Furthermore, contrary to the original definition of pheromones, many of the social chemosignals that robustly activate the AOS are not single compounds, but rather species-specific or individual-specific combinations of molecules in precise ratios (Wyatt 2009). Indeed, whereas pheromones are defined as intraspecies social signals that are “anonymous” with respect to the sender, many of the signals detected by the VNO serve to convey information about individuality (Hurst et al. 2001; Leinders-Zufall et al. 2004; Kaur et al. 2014; Ben-Shaul 2015). These include signature mixtures, which allow individuals or other social groups (e.g., families or colonies) to be recognized and distinguished. Finally, although pheromones, by strict definition, elicit a fixed and well-defined response, behavioral changes in response to many AOS signals can require learning and plasticity (Kaur et al. 2014; Xu et al. 2016), concepts that were long considered inapplicable to the AOS.

Signal Detection and Coding in the Accessory Olfactory System. Morhardt 2018

I’ll do this in order of information processing, from olfactory receptor, to olfactory bulbs, to feelings and actions related downstream brain meat.

Vomeronasal receptors, their ligands, and related feelings and behaviors.

A receptor is a protein that binds a specific molecule, its ligand. Here the ligands are odorants, and can be called vomerants for the ones that activate receptors in the VMO. There are 3 families of receptors typically found exclusively in the VMO. The interesting part is what binds them and the INNATE behavior effects that these ligands have (innate effects do not require previous experience).

Predators, and prey or food related vomerants.

Some creatures can leave scent trails that relate to preferred or safe food sources. Humans have a rich non-literal language for food and smells, things can “pass the smell test”. And humans have a language for other animals that we use as food sources, and unfortunately we treat one another as prey sometimes, grifters and “rubes” or “marks”.

Money might be in here as a “resource”. It’s not food but it has a sense of value from something.

First of all there chemicals related to predators and prey, or food in general. There is a chemical (2, 3, 5-trimethyl-3-thiazoline, TMT) from foxes that triggers freezing and flight in mice. Other predators can secrete other things too. Think about our language and how we can describe something as an external threat in a predatory sense. Rational or not. Something being “out to get you”, but not actually there at the moment.

One thing worth mentioning is how bigots, fascists and the like want to prey on other groups, but also have to spend so much time describing their prey as threats.

“Conspecific” related vomerants, peers at the species level.

Many of the following observations were taken from The Accessory Olfactory System: Innately Specialized or Microcosm of Mammalian Circuitry? Holy 2018

There are chemicals produced only by male mice that trigger aggression and territorial behavior in males and females (ESP1, ESP=exocrine gland-secreting peptide, from lacrimal glands). There are chemicals only in juveniles that suppress the adult sex drive (ESP22). There are chemicals only present when a female is ready to mate (sulfated estrogens). Our language is full of non-literal uses of male and female, there has to be brain hardware for “other kind in the same species” at the least. And “other kind” can be age and sex flavored. (There is ESP36, excreted by all females tested and a subset of male mice, I’ve no idea what to make of that but it’s curious.)

None of this is prescriptive, I’m about what can and has been done with our language, there’s plenty of room for how we get individually sensitive here. Think about “think of the children/women” language, directing feelings about threat and vulnerability there. Think about language involving sex, and just how sensitive society is to it. Some wring their hands at the mere technical mention of sex organs and actions. This place also suggests chemistry in caregivers that create feelings in offspring. Mother pigs secrete a substance that reduces aggression in their offspring while they are nursing. Pheromones, binding proteins, and olfactory systems in the pig (Sus scrofa): An updated review. Sankarganesh 2022.

There are whole sets of chemicals expressed in different amounts in individuals that can determine individuals or family groups. MUPs, major urinary proteins are examples. Feelings about siblings and kin. Found in urine. Piss. Mice have dozens of MUPs, we have a single pseudogene. Why can people get “pissed off”? Unless there is brain meat for urine sensitivity.

And family groups gets us to tribal behavior, your own kind as competitors. The feelings involved in our capitalist hellscape that pit us against one another. How migrants are characterized as “taking our jobs”, when supposed job creators love elimination of jobs when they can, moving them to other places if they can spend less. Or just get rid of other humans entirely.

There is the ability to detect other species as competitors. Smell if this or that kind of animal is present but not a predator. Think competing herbivores. The way bigots compare others to vermin like a nonconspecific competitor. Rats. Mix competitor and predator feelings and maybe you get the “deep state”, an attempt to define elected political opponents as threats.

There are chemicals in feces that activate the VMO too. Hints at processing of kinds of conspecifics and digestive status. Maybe that is why things can be “shitty”.

There are chemicals that activate the VMO related to infection too. Mice can detect sick conspecifics. The feelings about disease are rampant in bigotry. Think about the homophobes that need homosexuality to be more disease ridden and their language. Think about how the homeless, disabled, or mentally ill are often treated as untouchable. And people refrain from interacting. Or the use of disease applied to migrants. Disease feelings badly applied. Sensing and avoiding sick conspecifics requires Gαi2+ vomeronasal neurons. Weiss 2023.

Meat computer downstream from the VNO.

I first got interested in some of the following regions of the brain because they are relevant to tourette’s syndrome (TS). There was a study of children and adults with TS looking at  the volume of the amygdala and hippocampus. Morphologic Features of the Amygdala and Hippocampus in Children and Adults With Tourette Syndrome. Peterson 2008

The short version is the regions I’m about to mention are larger in TS. And I point out that tics and urges are made of feelings and actions. Actions that can be denied at the cost of increasing tension. Including mental actions, obsessions. In TS at least, but the phenomenon comes to us all when it is about what we feel strongly about.

Going back to the figure I made, the MOB and AOB are the main and accessory olfactory bulbs. This is where the olfactory neurons send their signal after binding an odorant. It looks like the location of chemical identity when I read about it. It’s what is downstream from the bulbs where things get interesting. Remember, humans don’t have an accessory olfactory bulb. But we have the downstream hardware and it’s fair to think of the vestigial imprint of the accessory olfactory system. Not strictly tied to male, female, offspring, parent etc, but based on it and more plastic, changeable in humans. A computational source of feelings in the meat computer that use and abuse in thought and language. Severed from olfaction by our evolution.

PMCo.

First there is the posterior cortical amygdala (PCo), which is subdivided into posteromedial (PMCo) and posterolateral (PLCo) sections. These regions are stereotyped as olfactory regions because they are primary olfactory cortex for the olfactory system. The AOB outputs to the PMCo (red) and the MOB outputs to the PLCo (green). We still have both brain regions, though they have lots of names in the history of brain science (superficial cortical region, sCLR…).

In mice these regions are necessary and sufficient to trigger innate feelings about positive and negative feeling odors like food or predator odor. Mice with no history with foxes will avoid this odor. Activation of these regions with various manipulations in locations can create attraction or avoidance to locations. Directly making a feeling without the smell. The participation of cortical amygdala in innate, odor-driven behavior. Root 2014

In mice the PMCo is involved in social long term memory formation. If a mouse is introduced to a food through another mouse it will strongly prefer this food. This is a process called Social transmission of food preference (STFP) by the paper. It even overrides innate preferences as mice innately prefer cocoa to cinnamon and STFP will override that. The cortical amygdala consolidates a socially transmitted long-term memory. Liu 2024.

Humans still have a PMCo. It’s hard to find information about it but a brain region used by our ancestors for feelings related to predators, food, prey and others of its own kind seems like a place that could still be used for the same feelings. In all their greatness and awfulness. While we no longer go sniffing others for information we senses used with those things.

What we have managed to discover in humans is that these regions are related to detection of emotions in facial expressions and language. Emotional faces, emotion and feeling in language. Selective processing of social stimuli in the superficial amygdala. Goossens 2009. Amygdala subregions differentially respond and rapidly adapt to threatening voices. Fruhholz 2013.

In case anyone is interested the PLCo seems to contain an approach-avoidance map along its rostral-caudal (“front” to “back” -ish) axis and is interconnected with the PMCo. Control of innate olfactory valence by segregated cortical amygdala circuits. Howe 2024. I wish they also checked the PMCo but they didn’t.

MEA.

The MEA is the medial nucleus of the amygdala. Where the posterior cortical amygdala seems to generate feelings, the MEA seems to generate actions. As I read about the amygdala and its subnuclei the MEA seemed to be about “interactions with other beings” as its activation and activity relates to attack, defense, mating, offspring care,… innately. Self-grooming too which might make it about the self as a being too.

It gets direct projections from both olfactory bulbs in mice, and of course lacks AOB projections in humans. Were your MEA stimulated you would feel a powerful urge to move. Development and function of the medial amygdala. Prakash 2025.

Where you have movement you have body maps. Anatomy connections. Powerful innate anatomy feelings are a potential biological substrate for profanity/vulgarity. While the MEA is about movement, the way these words are used are often very active “fuck off/fuck you” “don’t give a shit”, pissed off”, “don’t be a dick/pussy” (oh the gendered difference there!). “Full of shit” is qualitative, a feeling. If I tried “full of fuck” that’s action oriented. So is “full of piss and vinegar”.

I still have stuff to read about though because mere mentioning of someone’s “dick”, “ass”, “pussy”, or “tits” isn’t action oriented but creates a tension, a feeling. It’s just that actions require anatomy maps so this seems a potential place for anatomy feelings. Maybe not everything the MEA does is directly action oriented and it contains or connects to body maps somewhere, and connects to the posterior cortical amygdala (related to anatomy feelings via mating in the past and such in the past) that establish feelings in anatomy without actions. These regions are interconnected. Maybe there are anatomy maps in the PCo too, but mice seem to be choosing their actions via feelings there.

How do I end something like this? I feel like there is more to say but I’ve pretty much covered the things I wanted to. The neuroanatomy of cooties and cuss words. The vestigal accessory olfactory system and human feelings.