If I wanted to write about addiction today, my own NPR habit would be an excellent place to begin. News, blogs, radio, podcasts, it’s just so accessible! Today’s entry is not about addiction, but this story does start with “so I was reading NPR News…”

So I was reading NPR News, namely an article titled “What Makes You Feel Fear?” which turned out to be even more intriguing than I expected when I decided to read it. Evidently, researchers have used carbon dioxide inhalation to elicit panic and anxiety in patients with amygdala damage in both hemispheres: patients with no fear centers. How could this be?

(source: sciencedaily.com)

This startling discovery comes from a paper published this month in Nature Neuroscience by scientists at the University of Iowa. They tested three patients with Urbach-Wiethe disease (which resulted in bilateral amygdala lesions) by having them inhale CO₂. All three experienced panic attacks as a result, and showed significantly increased respiration rates – even with respect to healthy controls. This finding lead the authors to hypothesize that the amygdala may even be able to temporarily inhibit panic, as it has many GABAergic outputs to brainstem regions responsible for panic responses. All of this is pretty stunning. (Of course, the results would have been more stunning if there were a larger group of lesioned patients – all three of them did experience panic attacks in response to the CO₂ but so did three of the controls. Fortunately, though, people with bilateral amygdala damage are hard to come by. One could see how a lack of fear could be dangerous!)

The most curious question that this study evokes is whether there is a different mechanism for triggering fear in response to an internal stimulus (like inhaled CO₂) than there is for a response to an external stimulus (like a horror movie or a scary video game.) The amygdala is clearly implicated in the processing of inputs and outputs involved in fear responses, but how does it detect what it’s responding to in the first place?

Your amygdala definitely keeps you on the lookout for monsters in computer games like Amnesia: The Dark Descent! (source: amnesia-the-dark-descent.en.softonic.com)

A 2009 study published in Cell investigated this question in mice. Especially in light of the work in humans described above, the results are rather interesting. Another group of scientists looked at the acid-sensitive ion channel ASIC1a in mice as an indicator of the effects of CO₂ inhalation because it has been established that CO₂ inhalation results in a decrease in blood pH in mammals and generates a fear response. The researchers performed a number of experiments, and showed that the presence of this particular ion channel was necessary to evoke a freezing response in wild-type mice in the presence of 10% CO₂ and had no effect on knock-outs. They also looked at context conditioned fear responses with foot shocks – wild-type mice “froze” as expected, but in the presence of 10% CO₂ these mice showed freezing behavior before receiving the foot shocks. The next day, when returned to the context in which they were shocked (but not actually given shocks) the mice trained in the presence of CO₂ showed more freezing behavior than mice trained without it. In ASIC1a knockouts, the CO₂ exposure had no effect on context fear conditioning.

Then, the researchers looked directly at the effects of the CO₂ on amygdala pH, and when they confirmed that it was being lowered, they looked at firing rates of cultured amygdala neurons in response to lowered pH and saw an increase in firing as they brought the pH down in wild type cells. In line with these findings, the scientists figured that if low pH increased the fear response, perhaps it could be counteracted by raising amygdala pH with systemic injections of HCO₃ ^–. Indeed, this technique attenuated the fear response to CO₂ in wild-type mice but had no effect on knockouts. Lastly, by injecting a virus encoded with the ASIC1a gene to restrict its expression to the basolateral amygdala in knockout mice, the researchers restored the ability of these animals to demonstrate a fear response to inhaled CO₂.

All of this seems to indicate interoceptive capabilities in the amygdala. Even so…the knockout mice also showed an increase in ventilation in response to CO₂ inhalation, much like the lesioned patients in the human study – so the brain must have other detectors of acidosis…right? After all of this, does the amygdala play a chemosensory role? What other brain regions might be helping it out? Perhaps once we solve these puzzles, physicians may be able to take advantage of our brains’ pH sensitivity to treat panic and anxiety disorders.

What Makes You Feel Fear? – NPR

Fear and panic in humans with bilateral amygdala damage – Nature Neuroscience

The Amygdala Is a Chemosensor that Detects Carbon Dioxide and Acidosis to Elicit Fear Behavior - Cell

It’s Halloween, folks, and you know what that means: Jell-O molds of brains and punn-y costumes (Freudian Slip, anyone?), right? Amirite? Okay, maybe that’s just me, whatever, guys. But I can name at least one cherished Halloween pastime that tends to be pretty popular across the board, and that’s the horror movie marathon.

As we learned earlier this month, the mechanisms by which our brains process fear are intricate yet animalistic—after all, we’re by far not the only species that experiences the sensation of fear. Though what may be a uniquely human instinct is the propensity to actually seek out fear (and the sensation of arousal that inherently comes with it)—a concept illustrated nicely in this piece from The Dana Foundation. This purposeful seeking-out of fear-inducing stimuli is undoubtedly present in the act of partaking in the aforementioned horror movie marathon, and a particular subset of said scary flicks (and the characters therein) will serve as the main focus of this post.

There are lots of types of scary movies out there, from the psychological thriller to the slasher film and everything in between, but today, for the purposes of this entry, our interests lie in the psychopathic killers. Whether your allegiances fall with Freddy Kruger or Jason Voorhees, the psychopath is a popular character in cinema and in popular culture in general. But what makes this character profile so enjoyable and even attractive at times? And furthermore, what can we learn from the psychopaths among us?

A recent piece in Scientific American covered a conversation between psychologist Kevin Dutton of the University of Oxford and actor Michael C. Hall, the man behind America’s favorite serial killer, Dexter Morgan, of the hit Showtime series, Dexter. In his remarks and in his new book, The Wisdom of Psychopaths: What Saints, Spies, and Serial Killers Can Teach Us, Dutton asserts that possessing some of the qualities of a psychopath—ruthlessness, charm, inflated self-worth, lack of remorse and empathy, and the ability to manipulate others, to name a few—might not be all that bad.

Conventionally, we picture psychopaths as horrifying, antisocial killers and menaces to society, but Dutton argues that psychopathic tendencies fall on a spectrum (much like other psychological disorders), and those individuals that fall on the lower end can actually use these traits to their advantage. One of the examples he uses in his book (an excerpt of which can be found here, and is definitely worth a look), is that of a neurosurgeon. Ruthlessly cool and focused under pressure, and immune to emotional flair-ups of empathy and compassion in times of stress, the neurosurgeon (or any surgeon, for that matter) is a great example of someone who may possess psychopathic tendencies on some low level. Another prime example presented by Dutton is the business mogul—in order to climb to the top of a huge conglomerate, it’s imperative that some insensitivity, cutthroat ambition, and ruthlessness come into play.

In the context of the discussion, Michael C. Hall echoed Dutton’s claims that psychopathic tendencies can be a plus, saying he envies some of Dexter’s qualities, stress-management especially. And though we may not realize it consciously, the acceptance and even embracing of psychopathic traits isn’t uncommon. In his book, Dutton makes reference to an informal poll conducted in one of his classes in which students were presented with the aforementioned personality profile and asked what line of work might best suit someone who fits that description. Not surprisingly, their answers included CEO, spy, surgeon, and politician, as well as assassin and serial killer.

So what does this mean for the non-psychopathically inclined among us? And what does it mean for those who possess some of these traits? Could surgeons and CEOs be one step away from being the next Dexter Morgan or Hannibal Lecter? Probably not. As for everyone else, maybe we should try embracing some of our psychopathic tendencies, if we have them. It’s no surprise that characters like Dexter are so appealing to so many people (myself included)—though Dexter is on what Dutton would consider the higher end of the spectrum in terms of intensity of psychopathic qualities, a lot of those qualities are admirable ones, and ones that we would tend to seek out. So who knows, maybe you could be a psychopath, too.

Sources:

“Dexter” and British Psychologist Ask: Who Wants to be a Psychopath? – Scientific American

What Psychopaths Teach Us about How to Succeed [Exceprt] – Scientific American

Desperately Seeking Stimulation: Fear, Reward, and the Human Need for Novelty – The Dana Foundation