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napping bear. or, melodramatic thespian bear.  photos by olav thokle in alaska’s lake clark national park

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Is Your Nervous System a Democracy or a Dictatorship?

A single “dictator neuron” can take charge of complex behaviors

How does the architecture of our brain and neurons allow each of us to make individual behavioral choices? Scientists have long used the metaphor of government to explain how they think nervous systems are organized for decision-making. Are we at root a democracy, like the U.K. citizenry voting for Brexit? A dictatorship, like the North Korean leader ordering a missile launch? A set of factions competing for control, like those within the Turkish military? Or something else?

In 1890, psychologist William James argued that in each of us “[t]here is… one central or pontifical [nerve cell] to which our consciousness is attached.” But in 1941, physiologist and Nobel laureate Sir Charles Sherrington argued against the idea of a single pontifical cell in charge, suggesting rather that the nervous system is “a million-fold democracy whose each unit is a cell.”

So who was right?

For ethical reasons, we’re rarely justified in monitoring single cells in healthy people’s brains. But it is feasible to reveal the brain’s cellular mechanisms in many nonhuman animals. As I recount in my book “Governing Behavior,” experiments have revealed a range of decision-making architectures in nervous systems – from dictatorship, to oligarchy, to democracy.

A Neural Dictatorship

For some behaviors, a single nerve cell does act as a dictator, triggering an entire set of movements via the electrical signals it uses to send messages. (We neurobiologists call those signals action potentials, or spikes.) Take the example of touching a crayfish on its tail; a single spike in the lateral giant neuron elicits a fast tail-flip that vaults the animal upward, out of potential danger. These movements begin within about one hundredth of a second of the touch.

Similarly, a single spike in the giant Mauthner neuron in the brain of a fish elicits an escape movement that quickly turns the fish away from a threat so it can swim to safety. (This is the only confirmed “command neuron” in a vertebrate.)

Each of these dictator neurons is unusually large – especially its axon, the long, narrow part of the cell that transmits spikes over long distances. Each dictator neuron sits at the top of a hierarchy, integrating signals from many sensory neurons, and conveying its orders to a large set of subservient neurons that themselves cause muscle contractions.

Such cellular dictatorships are common for escape movements, especially in invertebrates. They also control other kinds of movements that are basically identical each time they occur, including cricket chirping.

Small Team Approach

But these dictator cells aren’t the whole story. Crayfish can trigger a tail-flip another way too – via another small set of neurons that effectively act as an oligarchy.

These “non-giant” escapes are very similar to those triggered by giant neurons, but begin slightly later and allow more flexibility in the details. Thus, when a crayfish is aware it is in danger and has more time to respond, it typically uses an oligarchy instead of its dictator.

Similarly, even if a fish’s Mauthner neuron is killed, the animal can still escape from dangerous situations. It can quickly make similar escape movements using a small set of other neurons, though these actions begin slightly later.

This redundancy makes sense: it would be very risky to trust escape from a predator to a single neuron, with no backup – injury or malfunction of that neuron would then be life-threatening. So evolution has provided multiple ways to initiate escape.

Neuronal oligarchies may also mediate our own high-level perceptions, such as when we recognize a human face.

Majority Wins

For many other behaviors, however, nervous systems make decisions through something like Sherrington’s “million-fold democracy.”

For example, when a monkey reaches out its arm, many neurons in its brain’s motor cortex generate spikes. Every neuron spikes for movements in many directions; but each has one particular direction that makes it spike the most.

Researchers hypothesized that each neuron contributes to all reaches to some degree, but spikes the most for reaches it’s contributing to most. To figure it out, they monitored many neurons and did some math.

Researchers measured the rate of spikes in several neurons when a monkey reached toward several targets. Then, for a single target, they represented each neuron by a vector – its angle indicates the neuron’s preferred reaching direction (when it spikes most) and the length indicates its relative rate of spiking for this particular target. They mathematically summed their effects (a weighted vector average) and could reliably predict the movement outcome of all the messages the neurons were sending.

This is like a neuronal election in which some neurons vote more often than others. An example is shown in the figure. The pale violet lines represent the movement votes of individual neurons. The orange line (the “population vector”) indicates their summed direction. The yellow line indicates the actual movement direction, which is quite similar to the population vector’s prediction. The researchers called this population coding.

For some animals and behaviors, it is possible to test the nervous system’s version of democracy by perturbing the election. For example, monkeys (and people) make movements called “saccades” to quickly shift the eyes from one fixation point to another. Saccades are triggered by neurons in a part of the brain called the superior colliculus. Like in the monkey reach example above, these neurons each spike for a wide variety of saccades but spike most for one direction and distance. If one part of the superior colliculus is anesthetized – disenfranchising a particular set of voters – all saccades are shifted away from the direction and distance that the now silent voters had preferred. The election has now been rigged.

A single-cell manipulation demonstrated that leeches also hold elections. Leeches bend their bodies away from a touch to their skin. The movement is due to the collective effects of a small number of neurons, some of which voted for the resulting outcome and some of which voted otherwise (but were outvoted).

If the leech is touched on the top, it tends to bend away from this touch. If a neuron that normally responds to touches on the bottom is electrically stimulated instead, the leech tends to bend in approximately the opposite direction (the middle panel of the figure). If this touch and this electrical stimulus occur simultaneously, the leech actually bends in an intermediate direction (the right panel of the figure).

This outcome is not optimal for either individual stimulus but is nonetheless the election result, a kind of compromise between two extremes. It’s like when a political party comes together at a convention to put together a platform. Taking into account what various wings of the party want can lead to a compromise somewhere in the middle.

Numerous other examples of neuronal democracies have been demonstrated. Democracies determine what we see, hear, feel and smell, from crickets and fruit flies to humans. For example, we perceive colors through the proportional voting of three kinds of photoreceptors that each respond best to a different wavelength of light, as physicist and physician Thomas Young proposed in 1802. One of the advantages of neuronal democracies is that variability in a single neuron’s spiking is averaged out in the voting, so perceptions and movements are actually more precise than if they depended on one or a few neurons. Also, if some neurons are damaged, many others remain to take up the slack.

Unlike countries, however, nervous systems can implement multiple forms of government simultaneously. A neuronal dictatorship can coexist with an oligarchy or democracy. The dictator, acting fastest, may trigger the onset of a behavior while other neurons fine-tune the ensuing movements. There does not need to be a single form of government as long as the behavioral consequences increase the probability of survival and reproduction.

Image Credit: Getty Images/iStockphoto (MARS)

Source: The Conversation (by Dr. Ari Berkowitz)

Llamagirl.

I know it’s selfish of me, but I hope you get to see this. I hope that one day, while you’re scrolling through tumblr, you’ll see this post. 

I’ve been told I’m delusional, and that I think too big for my dreams to come to reality. But that’s just who I am. When I first held you on the bus, I wasn’t in a good place. You didn’t know it at the time, but you being there, you just... existing with me during those moments on the bus, they made everything so much better. I still dreamt big though.

 I would think of these fantastical delusions where the whole world was our playground, where nothing could ever hurt you or me again, and we could just be together, forever. Other times, I would just wish that I could stop time, so that I could hold you in my arms forever and not have to dread the return home.

Home. That’s a word filled with both joy and bitterness. At home, no matter where I’ve been, I’ve been hurt, and I have hurt others. I know I deserve what’s coming to me, because my mind doesn’t stop. Hurting people in your mind is fine, but when it becomes so graphic, and you take joy out of delivering brutal pain upon those you hate and despise, it makes you wonder if you are even a good enough human being to stay alive. I can’t say it here, because if I were caught with evidence like this, I could possibly be sent to a mental hospital for the violent urges and obsessive fantasies. Don’t worry, I’ve researched this, I’m not going to stupidly incriminate myself. I’ll tell you the thoughts and fantasies if you want me to, just give me time, enough time so that I won’t regret it immediately after I said it. 

Your eyes are beautiful, you know? They have a sort of radiance to them. To me, it’s a pathway, one that takes me away from all the stress and pain, and allows me to enter a temporary Haven ( or is it Heaven?), for just a little while, at least. Sometimes I ask you if i can just look at you, you might have noticed cuz you seem to find it a tad odd jajaja. I do it for a reason. I want to look at you, to fall in your eyes and never come out. If I were there with you, I would take off your glasses, and tell you how beautiful you are both with and without them, and I would stare into your eyes for hours. That is, if you would let me, of course. They’re magical honestly; your eyes encaptured me in delightful rapture right before I first kissed you. 

A funny thing you should know about me, most people tend to think that I look at them directly in the eyes, but I actually get way too shy for that. To remedy this, I typically look right below their eyes, between the cheekbone and the actual eye; at about the Palpebromalar groove, if you want me to be even more specific. I know how you love detail. It’s a pretty good way to avoid actual eye contact honestly, it makes it less awkward because I feel less inclined to look away. But see, that changed with you. I always wanted to look at you in the eye, and I always did my best to, but I was too scared that I would look away. But then, at Paseo, when you told me you were going to leave, I made a choice. I was going to kiss you, and I was going to look into your eyes. And it was so, so beautiful. I don’t think you noticed, but I felt my face becoming flushed just by looking at you. That never happened with anyone else, not like this. My face never gets flushed, but you managed to stir something in me that made me want to look into your eyes forever. 

And then came your lips. It was hilarious how we initially failed in the kiss, so I kissed your cheeks. They were so soft, I wanted to keep kissing them nonstop. But I saw that you were really shy about this, but also really looking forward to it. I didn’t want to make you wait any longer, and honestly, I don’t think I could have waited any longer myself; I’ve been wanting to kiss you for an infinitely long time. The first kiss, I held it for a while, I wanted to see what you would do, because I didn’t want to stop. It was too good, too addicting, too amazing to just stop like that. After that first kiss, I just wanted more, and It made me so happy that you wanted it too. You looked so happy, so excited, so full of life. It’s like something lit up inside you, like all that tiredness and pain that you’ve been going through had just disappeared, for just a little while. And it disappeared for me too, honestly. I was extremely suicidal back then, but on that day, at Paseo, I didn’t think of hurting myself, I didn’t even think of hurting others; the only thing on my mind was, “God I hope my breath doesn’t smell bad.” 

It was at that point that I wanted to make you happy. I wanted to make you smile. Yes, I felt a bit of fear because I didn’t feel capable of doing so, but I would be damned if I didn’t fucking try. And I hope I’ve done well up until now.

Well, if I’m being honest, I know I haven’t done well. I’ve hurt you, I’ve broken your trust and I proved that I’m completely irresponsible. That’s why I’ve been working my ass off to be a better man. Yes, man. I want to be that man for you, not just a boy or kid or guy, I want to be a man. The one who you can trust, who you can love without feeling like I’m going to just let you down again like I have so many times in the past. By the time I arrive in Ecuador, I will be at least a 20% cooler Gabe, I assure you, with a 45% increase in responsibility and 5% less jealousy (I’m working on the jealousy, that gonna take some time, but don’t worry, I’m aiming to reduce it by 20% next year to make up for it).

Let’s go back to the word “Home” for a bit, shall we? I have some things I need to get off my chest, and I feel like you deserve to know. Let’s start with Chile. I never really recognized Chile as my home, considering the fact that I lived in it for only my first two years of infancy with a total of 20 month’s worth of visiting over 19 years. I still identify as Chilean, and it really bothers me that you joke about me being more gringo than Chilean, but I know that you only tease, so it really is fine, you know? Speaking of gringo, lets get into the US. I’ve lived in the US for a total of 12 years with about four months total of visiting throughout my four years in Ecuador, give or take a month or two. You, like so many others, joked that I was extremely gringo, but honestly, I don’t think I am. I can’t really identify myself with the US. Yes, it’s been my home for a disgustingly long amount of time, but that doesn’t mean that it actually was my home. I felt homey at the beginning because I didn’t really know any other place, and because my family was there. But then Simon left. He graduated from the University of Maryland, he did spectacular apparently. I actually tried to ignore the fact that he was leaving though, as if I just refused to accept that he would no longer be a part of my life. And for a while, it was okay. What really hit me was my sister’s departure. She had just graduated from Churchill High School, and she got accepted into La Universidad Catolica de Chile, which was fucking amazing! But again, I chose to ignore it. In fact, according to her, she didn’t even want to go! She wanted to study in the US, in Maryland. But my parents had some massive turmoil at that point, so they pretty much forced her to go to Chile, but I didn’t know this until much later. To be honest, I don’t think that I will ever feel as abandoned as I did then. My sister, who would protect me from my father’s temper, who would clean up my tears, who would promised to be there for me always, just disappeared. We didn’t really talk for about two years after that. Yes, I would visit Chile, and I would tell her EVERYTHING in my life, but it was still super awkward between us.  It’s funny though, whenever my mom and I flew back to the US after visiting Chile, I would just be bawling my eyes out, begging to see my sister again and I would apparently wonder why she left in the first place. I was heartbroken that my sister cared so little about me, or so I thought. I think that’s the reason why I want you to spend so much time with your sister, because even though she’s super angsty and acting like a total teen by ignoring you, it’s going to hurt when you leave for university, for the both of you. What made the pain worse for me was the fact that I was left alone, between two warring parties: Dad and Mom. The short tempered man who I was terrified of, or the sweethearted woman who knows exactly what strings to pull to make it seem like she was the victim. My mom definitely isn’t perfect, I hope you know that. She has a very dark side that she shows much less of now, but then again, don’t we all? I became a very good liar because of my parents, you know? I’ve only cried two times because of the divorce when I was younger: when my father broke down because he knew that I wasn’t going to live with him, and when he said that he would leave me if I wanted him to. Those were very extreme situations, so they don’t count. I would look like a total asshole if I didn’t cry at those times. Then again, I am a total asshole, so it would have actually matched the personality, but oh well, I wasn’t strong enough to hold back those tears. But I did hold them back for the rest of middle school. When you make someone choose between two things, you have to make sure that the person is ready for such a big responsibility. We take choice for granted, because it gives us so so much power, but for an 11 year old boy, choosing between your parents is absolutely soulcrushing. I did it anyways though, I didn’t have much of a choice in the first place. I’m pretty sure I would have killed myself if they stayed together and fought so often like they did before, especially now that I had no one to help me ignore the fights, to ignore the fear, the pain, and the uncertainty. But now it all came to me. Once I chose my mom over my dad, my first depressive thought came in; I thought, “Am I even worth it?” “Am I even worth all this pain and suffering? All this fighting? I’m just a chubby kid who’s the son of two extremely powerful, very intelligent people, why the hell are they fighting over me?” “Why do they even love me?” A few months later, after constant fights with my mom, I finally began thinking, “Do they even love me in the first place? Or am I just a tool for them to use to hurt each other?” That kinda made the resentment worse, if I’m being honest. It didn’t really help much. The fights between me an my mom got worse. We would fight every night, whenever she came home from work. Eventually, I reached a point to where I didn’t even remember what it felt to have just ONE FUCKING DAY where we didn’t fight. Of course it was all my fault though, I was always the one who instigated the fighting, because I was so angry and resentful that I had to force myself to be happy for them. But them my mom left for Haiti in 7th grade. I didn’t cry in front of her, but I did whenever I went to bed. I felt abandoned again. I felt abandoned by two people; my sister, and my mom. Now I know that that wasn’t really the case, my mom got paid a hell of a lot for going to Haiti, so it really was worth it, I guess. I’m skeptical of that part, considering that I was constantly scared that something was going to happen to her. There was a German UN worker there, she was reckless and made a mistake that led to her being kidnapped, raped, beaten and held for ransom by Haitan narcos. Can you really blame me for being scared? I was terrified. We talked by skype every night, but we still fought. I fought with my caretaker, my tutor, everyone who I knew I could control. I’m a real piece of shit honestly, because even though I didn’t know the word for it back then, I knew exactly what I was doing: manipulating. I manipulated others to feel bad so that it would be me who had to forgive them, no the other way around. This worked for my tutor, but not for Karin, my caretaker at the time. She was a badass Chilean with a lot of Mapuche blood, she didn’t take shit from anyone, and I’m grateful for that. She helped me grow up, she helped me see that I was being a little asshole who needed to learn that hurting others isn’t the way to resolve one’s own pain. School was actually a vessel for me, a way for me to get away and forget the problems I had at home. I worked my ass off, and I did excellent, but I didn’t really care for it, it was just a way to forget. I did my best to ignore my dad as much as I could during that time, I was too afraid to be angry at him. You haven’t seen him angry; he’s terrifying. Whenever I would visit him at his house, which was every other weekend, I would spend most of my time avoiding him by going on my laptop or playing video games. I hated him because I felt that his way of dealing with his anger wasn’t fair, because he would scream at me or hit inanimate objects. I think you can see where my temper came from. My mom would come to visit every month or so, and for those days, we wouldn’t really fight at all, but it felt so... uncomfortable and alienating that she was there. It was like, I had forgotten how it felt to have a parent around. I forgot to mention that when my mom left to Haiti, I didn’t go to live with my dad until the last few months of my final year of middle school; for the most part, I lived with Karin, who did a pretty excellent job of taking care of me, honestly. I began going out with my friends a bit more often in 8th grade. We would play Capture the Flag, Soccer, Football, the works. It was honestly the funnest time I had. I wish I got to spend more time with them. The group varied at time, but they were mainly: Vicente Rudolph (my best friend outside of school), Maiu Romano, Daniel Espinoza, Charles Grody, Peter Harich (that guy was crazy, pretty cool though), Leetal, Mackenzie, and two others that I don’t remember. Oh yes, and Rodrigo Lamas! He and I were super close. It sucked that he ignored me once I came to visit. Oh well. I still have those memories, and I’ll honestly treasure them forever. They made me feel like I was a part of something, like I wasn’t completely alone. With them, I was actually happy. But with all good things, they must end. Thus came the move. I had to move to Ecuador, so I had to say goodbye to all my friends. I forgot to say, I hung out with a different group of people in school and out of school. The one’s I hung out in school were Trayell Sponge (my best friend and someone who always knew what to say to make me laugh), Dylan, Brandon (aka Bahram) Esmailian, Josiah Wedgwood, two William Chens, and Jared. They were such a badass group, I loved them. I remember that when I told Tray that I was going to leave for Ecuador, he punched the lockers so hard he left a dent, and was immensely pissed off for some reason. “It’s total fucking bullshit,” I remember he said. I remember that he and I tried to keep talking while I was in Ecuador. It didn’t work out, mainly because we both were just too busy with other things. In the end, I couldn’t even find him again, he deleted his goddamned facebook account. I wonder how he’s doing. And voila! I was then in Ecuador! I would go into further detail as to what happened, but this section is wayyy too long already, and I’m starting to feel self-conscious. Besides, you know most of the Ecuador section already. I’m sorry for making this section so long, It was really something that I needed to talk about.

Wow, that took a MASSIVE load off. It feels nice to be able to talk about this stuff. Now, where was I? Oh, yes, you. Wonderful, amazing, beautiful you. I wasn’t lying when I said that you had saved my life you know? Every day I would go home from school, hoping that the  bus would crash or I would get shot, just so that I wouldn’t have to go back home. The bus the was the only escape for me. I constantly thought of it, you know? Suicide. At one point in time, it was literally the only thing on my mind. It made me see how worthless I was, and even though I am much, much better now, I still feel that sometimes. In my opinion, depression can be used as a lense to see oneself at our worst, and we can use that to see all the improvement we’ve made ever since we came to realize all the awful things about ourselves. But you know what I found funny? There wasn’t anything wrong with you. Yes, you had a dark past regarding certain things that I will not get into, but to me, you were still that perfect girl who made me smile. Yes you made mistakes, you fought with your parents, but so did I! And the thing is, I always felt like I could find comfort in you, like you always knew how I felt, and most importantly, you treated me like a human being. I didn’t feel like that with the Seniors honestly, it felt like they were friends with me just for the sake of being friends, not because they actually liked me. Yes there were exceptions, but it was still very frustrating to live in a group that you know you don’t always fit in with. Honestly, both of us have our bad sides and issues, but we also have the side that makes us beautiful and amazing; that’s what makes us human. We are an explosive mixture of all the evil in the world mixed with all the good in the world, and for the first time in a long time, I feel that I can finally say this truthfully: I absolutely fucking love it. I love how humans are hybrids between perfection and mistakes. It makes me see us as humanely perfect, if that makes sense? Like, in the perspective of a human, we are all perfect, because everyone is a unique mixture of good and bad that leads us to a chain of events called life, and we all just want to do just these few things in our rather short lifespan: to fit it, to be happy, and to succeed. That is what makes us so humanely perfect, the fact that we are hybrids of two opposing sides and that we all strive for the very same goal. To me, you aren’t perfect, and I’m not perfect to you, not in the way other people see it at least. We humans make too many mistakes to be called perfect, because we see perfection as a godlike form in which one cannot make any mistakes or fuck up once in a while, but I call bullshit on that. We are perfect, in our human form. We humans fuck up, and that makes us grow and learn and improve, and that makes us perfect, because whether we know it or not, we become better, because we want to be perfect, even though it’s absolutely normal for us to make mistakes throughout our lives. So, in human terms, the fact that we make mistakes but improve upon them, that makes me see us as perfect, because we grow and we learn, even through our vices and mistakes, we are still humanely perfect. 

Maybe that last section didn’t make any sense... sorry about that, I’m a tad sleep deprived, I’ve been writing this for about 3 or so hours now and I’m now entering the wee hours of the morning, so I may become a tad incoherent. 

Nonetheless, I’ve told you a bit about myself, and how I see us as humans, and now I just want to say one thing: I love you. I adore you. To me, your hair can be seen as a rainbow of flowing shimmering locks of hair, and your beautiful eyes are the moon and the sun to me, because it feels like you are there to protect me no matter what. Your voice is the wind to me, how it flows so gently and kisses my face and hugs my body so gently, to show your love for me. Your laughter is the sound of pure happiness, which approaches me whenever I get on skype, because I know that the ringing calling of skype means that I’m just seconds away to hearing your voice. As I’ve said before and I’ll say again, I feel lost without you. You’ve guided my way through so many hard times, and I hope I’ve done the same for you. We’re in this together through thick and thin, no matter how many fights we get into or how angry we are at each other, I still love you, and i still remember all the good, amazing memories we’ve made together, because I will cherish those till the end of my existence, but I hope my existence can end next to your side, when we’re both old enough. You are my love, mi amor, mi vida, my always, and I love you infinitely, please don’t ever forget that. The future is very uncertain, that is for sure, but it’s like you’ve said, “I’m not sure about a lot of things, but I am certain of one thing. And that is that I love you.” Sorry, I may have messed up the wording a tad, but you know what I mean. I too am uncertain about so many things, I just try not to show it. But I am certain that I love you, infinitely and truly. I used to wonder about my future, and if I ever deserved to have one in the first place, but whenever I look at you, I know that I want to keep going, through the good and the bad, that eventually, It’ll all be worth it. You make me want to be a better person, for myself as well this time. I want to be better, because I want to succeed and do great things in life. I want to be happy. Specifically, I want to be happy with you. 

I don’t feel like I’m enough just yet, but that’s something I need to keep working on so that I am enough. I will make you the happiest girl in the world, you just wait and see. 

You must be getting a stroke from all the cheesiness I’ve been saying, and I want to keep going, but I know that If I do I just won’t stop, and I need to post this eventually! Maybe I’ll write another message defining all the ways that you amaze me and make me appreciate you as the amazing, beautiful person you are, but thats for next time. 

For now, I love you infinitely mi amor, so much so that the universe itself cannot contain my love. I want to see you now, so so much that it’s killing me. But i’ll just have to wait. I’ll be there soon, so that I can hold you in my arms again. One month left, please wait for me like I’m waiting for you, I love you 

<3

- GQ

“It’s chaos. Be kind.”

as you get older, you realize that you’re not always right and there’s so many things you could’ve handled better, so many situations where you could’ve been kinder and all you can really do is forgive yourself and let your mistakes make you a better person.

Is an immunization for stress on the horizon?

Can probiotics fend off mood disorders?

It’s too early to say with scientific certainty, but a new study by CU Boulder researchers suggests that one particular beneficial bacteria can have long-lasting anti-inflammatory effects on the brain, making it more resilient to the physical and behavioral effects of stress.

The findings, if replicated in clinical trials could ultimately lead to new probiotic-based immunizations to protect against posttraumatic stress disorder (PTSD) and anxiety or new treatments for depression, the authors say.

“We found that in rodents this particular bacterium, Mycobacterium vaccae, actually shifts the environment in the brain toward an anti-inflammatory state,” said lead author Matthew Frank, a senior research associate in the Department of Psychology and Neuroscience. “If you could do that in people, it could have broad implications for a number of neuroinflammatory diseases.”

Anxiety, PTSD and other stress-related mental disorders impact as many as one in four people in their lifetime. Mounting research suggests that stress-induced brain inflammation can boost risk of such disorders, in part by impacting mood-influencing neurotransmitters like norepinephrine or dopamine.

“There is a robust literature that shows if you induce an inflammatory immune response in people, they quickly show signs of depression and anxiety,” said Frank. “Just think about how you feel when you get the flu.”

Research also suggests that trauma, illness or surgery can sensitize certain regions of the brain, setting up a hair-trigger inflammatory response to subsequent stressors which can lead to mood disorders and cognitive decline.

“We found that Mycobacterium vaccae blocked those sensitizing effects of stress too, creating a lasting stress-resilient phenotype in the brain,” Frank said.

A previous CU Boulder study, found that mice injected with a heat-killed preparation of M. vaccae and then placed with a larger aggressive male for 19 days exhibited less anxiety-like behavior and were less likely to suffer colitis or inflammation in their peripheral tissues. For the new study, published in the journal Brain, Behavior and Immunity, the researchers set out to determine what exactly M. vaccae does in the brain.

Male rats injected with the bacterium three times, one week apart, had significantly higher levels of the anti-inflammatory protein interleukin-4 in the hippocampus — a brain region responsible for modulating cognitive function, anxiety and fear — eight days after the final injection.

After exposure to a stressor, the immunized animals also showed lower levels of a stress-induced protein, or alarmin, called HMGB1, believed to play a role in sensitizing the brain to inflammation, and higher expression of CD200R1, a receptor key for keeping glial cells (the brain’s immune cells) in an anti-inflammatory state. As in the first study, the immunized rats exhibited less anxious behavior after being stressed.

Mood-modulating microbes

“If you look at the field of probiotics generally, they have been shown to have strong effects in the domains of cognitive function, anxiety and fear,” said senior author Christopher Lowry, an associate professor in integrative physiology. “This paper helps make sense of that by suggesting that these beneficial microbes, or signals derived from these microbes, somehow make their way to the hippocampus, inducing an anti-inflammatory state.”

M. vaccae was first discovered on the shores of Lake Kyoga in Uganda in the 1990s by immunologists who realized that people who lived in the area responded better to certain tuberculosis vaccines. They later realized that the bacterium found in the lakeshore soil had immune-modulating properties that were enhancing the vaccine’s efficacy. Researchers set out to study it in lung cancer patients and found that, while it did not prolong life, it somehow improved mood.

M. vaccae is not commercially available but is the subject of numerous ongoing studies.

Lowry, who has been studying it for 17 years, envisions a day when it or another beneficial bacteria could be administered to people at high risk of PTSD – such as soldiers preparing to be deployed or emergency room workers – to buffer the effects of stress on the brain and body. It could also possibly be used to prevent sepsis-induced cognitive impairment, he said.

Meanwhile, he is working with researchers at University of Colorado Denver on a study exploring whether veterans with PTSD can benefit from an oral probiotic consisting of a different bacterial strain, Lactobacillus reuteri.

“More research is necessary, but it’s possible that other strains of beneficial bacteria or probiotics may have a similar effect on the brain,” he said.

The Way brothers