From Nose to Brain: The Neurology of Smell

Question: Are olfactory signals processed in your brain in a similar fashion to visual or auditory signals?

Stuart Firestein: So the olfactory neurons once they bind this odor molecule and change as I say, their electrical quality, the voltage if you will, across their membrane this signal is transmitted to the brain down a long cable-like structure called an axon, which most brain cells have. It goes through a very thin bone and into a region of your brain called the olfactory bulb, a very small chunk of your brain that actually hangs under the bottom of your brain just kind of behind your eyes if you will. And there they make a connection with another set of neurons, so a connection that we call a synapse and they make a connection with another set of neurons, which then transmits the message to the next step in the brain.

So the first step, the first relay station is the olfactory bulb and from there the signal is sent mostly to an area, specialized area of cortex, of brain cortex called the piriform cortex. Now this pathway is unusual because the other senses typically from the primary tissue—the retina or the auditory, the hair cells of the auditory or the cochlea—send their signals first to a tissue in the center of the brain, an organizing region in the center of the brain called the thalamus. And there the signals are sorted and standardized and then moved out into specialized area of the cortex—the visual cortex at the back of your brain, the auditory cortex on the side of your brain—for further processing and presumably building up into a perception. I’m waving my hands a bit here because we really don’t understand so much about those processes yet, although we’re beginning to.

The olfactory system is a bit unusual in that way in that it does not go through the thalamus. At some point later in the progress of olfactory information there is an offshoot of some of the fibers that do go to thalamus, but it’s rather minor. So instead in the olfactory system you go from the sensory neurons to this olfactory bulb structure where there is a synapse with another kind of cell. It’s called a mitral cell—and those mitral cells take in information from lots of different sensory neurons and decide what is being smelled out there, because of course most of the time we don’t smell a single molecule, we smell a blend of molecules. Usually a complex blend of molecules and so pulling that all apart is at least partly the job of these mitral cells to which the olfactory sensory neurons make a connection. The mitral cells then make some decisions, if you will. They integrate information and they have an axon also, a long cable that goes to this area of the brain called the piriform cortex where they synapse, make connections with yet another cell.

So what is remarkable about this in the olfactory system is that from the outside world to cortical tissue, which is the highest level of brain tissue we have, there are only two synapses, two connections, one between the sensory neuron and the cells in the olfactory bulb and then between these olfactory bulb cells, the mitral cells and those in the piriform cortex.

In any other system you wouldn’t be anywhere yet. In the visual system you’d still be in the retina after two synapses. You wouldn’t have even gotten to the inner retina let alone to the thalamus or to the visual cortex, which is six or seven synapses away. The same thing is true of auditory system and many other sensory systems including taste by the way, the actual taste system. There are at least three, four, five synapses to get you to cortical tissue whereas the olfactory system has this very immediate access to the cortex.

Recorded September 22, 2010
Interviewed by Andrew Dermont

Image courtesy of Flickr user Greencolander.

What’s remarkable about the olfactory system is that from the outside world to the highest level of brain tissue there are only two synapses.

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Politics & Current Affairs

Political division is nothing new. Throughout American history there have been numerous flare ups in which the political arena was more than just tense but incideniary. In a letter addressed to William Hamilton in 1800, Thomas Jefferson once lamented about how an emotional fervor had swept over the populace in regards to a certain political issue at the time. It disturbed him greatly to see how these political issues seemed to seep into every area of life and even affect people's interpersonal relationships. At one point in the letter he states:

"I never considered a difference of opinion in politics, in religion, in philosophy, as cause for withdrawing from a friend."

Today, we Americans find ourselves in a similar situation, with our political environment even more splintered due to a number of factors. The advent of mass digital media, siloed identity-driven political groups, and a societal lack of understanding of basic discursive fundamentals all contribute to the problem.

Civil discourse has fallen to an all time low.

The question that the American populace needs to ask itself now is: how do we fix it?


Discursive fundamentals need to be taught to preserve free expression

In a 2017 Free Speech and Tolerance Survey by Cato, it was found that 71% of Americans believe that political correctness had silenced important discussions necessary to our society. Many have pointed to draconian university policies regarding political correctness as a contributing factor to this phenomenon.

It's a great irony that, colleges, once true bastions of free-speech, counterculture and progressiveness, have now devolved into reactionary tribal politics.

Many years ago, one could count on the fact that universities would be the first places where you could espouse and debate any controversial idea without consequence. The decline of staple subjects that deal with the wisdom of the ancients, historical reference points, and civic discourse could be to blame for this exaggerated partisanship boiling on campuses.

Young people seeking an education are given a disservice when fed biased ideology, even if such ideology is presented with the best of intentions. Politics are but one small sliver for society and the human condition at large. Universities would do well to instead teach the principles of healthy discourse and engagement across the ideological spectrum.

The fundamentals of logic, debate and the rich artistic heritage of western civilization need to be the central focus of an education. They help to create a well-rounded citizen that can deal with controversial political issues.

It has been found that in the abstract, college students generally support and endorse the first amendment, but there's a catch when it comes to actually practicing it. This was explored in a Gallup survey titled: Free Expression on Campus: What college students think about First amendment issues.

In their findings the authors state:

"The vast majority say free speech is important to democracy and favor an open learning environment that promotes the airing of a wide variety of ideas. However, the actions of some students in recent years — from milder actions such as claiming to be threatened by messages written in chalk promoting Trump's candidacy to the most extreme acts of engaging in violence to stop attempted speeches — raise issues of just how committed college students are to
upholding First Amendment ideals.

Most college students do not condone more aggressive actions to squelch speech, like violence and shouting down speakers, although there are some who do. However, students do support many policies or actions that place limits on speech, including free speech zones, speech codes and campus prohibitions on hate speech, suggesting that their commitment to free speech has limits. As one example, barely a majority think handing out literature on controversial issues is "always acceptable."

With this in mind, the problems seen on college campuses are also being seen on a whole through other pockets of society and regular everyday civic discourse. Look no further than the dreaded and cliche prospect of political discussion at Thanksgiving dinner.

Talking politics at Thanksgiving dinner

As a result of this increased tribalization of views, it's becoming increasingly more difficult to engage in polite conversation with people possessing opposing viewpoints. The authors of a recent Hidden Tribes study broke down the political "tribes" in which many find themselves in:

  • Progressive Activists: younger, highly engaged, secular, cosmopolitan, angry.
  • Traditional Liberals: older, retired, open to compromise, rational, cautious.
  • Passive Liberals: unhappy, insecure, distrustful, disillusioned.
  • Politically Disengaged: young, low income, distrustful, detached, patriotic, conspiratorial
  • Moderates: engaged, civic-minded, middle-of-the-road, pessimistic, Protestant.
  • Traditional Conservatives: religious, middle class, patriotic, moralistic.
  • Devoted Conservatives: white, retired, highly engaged, uncompromising,
    Patriotic.

Understanding these different viewpoints and the hidden tribes we may belong to will be essential in having conversations with those we disagree with. This might just come to a head when it's Thanksgiving and you have a mix of many different personalities, ages, and viewpoints.

It's interesting to note the authors found that:

"Tribe membership shows strong reliability in predicting views across different political topics."

You'll find that depending on what group you identify with, that nearly 100 percent of the time you'll believe in the same way the rest of your group constituents do.

Here are some statistics on differing viewpoints according to political party:

  • 51% of staunch liberals say it's "morally acceptable" to punch Nazis.
  • 53% of Republicans favor stripping U.S. citizenship from people who burn the American flag.
  • 51% of Democrats support a law that requires Americans use transgender people's preferred gender pronouns.
  • 65% of Republicans say NFL players should be fired if they refuse to stand for the anthem.
  • 58% of Democrats say employers should punish employees for offensive Facebook posts.
  • 47% of Republicans favor bans on building new mosques.

Understanding the fact that tribal membership indicates what you believe, can help you return to the fundamentals for proper political engagement

Here are some guidelines for civic discourse that might come in handy:

  • Avoid logical fallacies. Essentially at the core, a logical fallacy is anything that detracts from the debate and seeks to attack the person rather than the idea and stray from the topic at hand.
  • Practice inclusion and listen to who you're speaking to.
  • Have the idea that there is nothing out of bounds for inquiry or conversation once you get down to an even stronger or new perspective of whatever you were discussing.
  • Keep in mind the maxim of : Do not listen with the intent to reply. But with the intent to understand.
  • We're not trying to proselytize nor shout others down with our rhetoric, but come to understand one another again.
  • If we're tied too closely to some in-group we no longer become an individual but a clone of someone else's ideology.

Civic discourse in the divisive age

Debate and civic discourse is inherently messy. Add into the mix an ignorance of history, rabid politicization and debased political discourse, you can see that it will be very difficult in mending this discursive staple of a functional civilization.

There is still hope that this great divide can be mended, because it has to be. The Hidden Tribes authors at one point state:

"In the era of social media and partisan news outlets, America's differences have become
dangerously tribal, fueled by a culture of outrage and taking offense. For the combatants,
the other side can no longer be tolerated, and no price is too high to defeat them.
These tensions are poisoning personal relationships, consuming our politics and
putting our democracy in peril.


Once a country has become tribalized, debates about contested issues from
immigration and trade to economic management, climate change and national security,
become shaped by larger tribal identities. Policy debate gives way to tribal conflicts.
Polarization and tribalism are self-reinforcing and will likely continue to accelerate.
The work of rebuilding our fragmented society needs to start now. It extends from
re-connecting people across the lines of division in local communities all the way to
building a renewed sense of national identity: a bigger story of us."

We need to start teaching people how to approach subjects from less of an emotional or baseless educational bias or identity, especially in the event that the subject matter could be construed to be controversial or uncomfortable.

This will be the beginning of a new era of understanding, inclusion and the defeat of regressive philosophies that threaten the core of our nation and civilization.