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?
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!)
Ever been in a situation where you had to deal with someone/something that just really PISSED YOU OFF!? Of course you have. After all, we're all human; we've all felt that terrible tingle of insatiable rage wash over us from time to time. It's a pretty intense emotion, sometimes even frightening in its potential to completely change your whole disposition from that of a mild mannered undergrad to a rampaging Hulk wannabe. Even more interesting (and a bit more terrifying perhaps) is how such an big emotion like anger can be generated by such a tiny section of your brain!
Despite the nigh inevitable incorporation of the frontal lobe in interpreting and modulating emotional responses, when it comes to generating many of the basic motivated behaviors to which mammals are bound (anger, fear, attraction, hunger/thirst, etc.) the amygdala is usually the primary suspect (or at least an important accomplice). The amygdala itself is a tiny, almond shaped bundle of neurons and fiber tracts located deep within the temporal lobes (usually near the end of the hippocampus). Countless studies from emotion-based research have targeted the amygdala as a playing a minor role in memory and, most famously, as a hot spot for emotional response. Despite all this work, researchers are still relatively hazy as to how the amygdala is able to help us feel such different emotions as fear, anger and so on. However, recent research from the Howard Hughes Medical Institute at Caltech may be starting to turn all of our uncertainty about the amygdala around, as well as shedding some light on the specific neuronal origins of our most primal emotions.
Current investigations from the labs of Dayu Lin and David Anderson have led to the discovery of what seems to be a subset of neurons in the amygdala that exclusively help generate aggression in mice. Upon activation, these "rage" neurons (or "fight cells" as Anderson has dubbed them) can turn an otherwise docile male mouse into a hyper-aggressive brawler. Indeed, the effects are so strong that the mice can be induced to attack females and other males (usually castrated) that would otherwise not be viewed as a threat. Talk about domestic violence! To tease apart the action and sensitivity of these cells even more, Anderson and his team genetically modified a strain of these mice to express fight cells that respond to pulses of laser light. Upon shining this light in the eyes of mutated mice, an aggressive response in the presence of females, castrated males and even a rubber glove was able to be stimulated!
In the midst of all this bio-molecular wizardry, Anderson and his team stumbled across another interesting discovery: a population of "mate" stimulating cells that seems to be closely knit with the fight cells in the amygdala. As the name may imply, mate cells seem to play a large role in inducing and modulating sexual behavior. Interestingly though, upon analyzing the brains of modified mice, after having previously been induced to attack a rubber glove (or something similar) and then allowed to mate, Anderson's team that a healthy amount of fight cells were activated in concert with mate cells as the mice where engaging in sexual activity.
It is this latest discovery that Anderson and his team have expressed the most excitement about, specifically because of its implications for potential remediation of violent sex offenders and predators who may be suffering from a massive "cross-wiring" of the fight cells and mate cells in their amygdalar/temporal regions. If enough homology can be drawn between these cells and their specific pathways in the mouse brain with that of the human brain, perhaps the future work of Hughes center could produce ways to untangle these connections and offer both sex offenders (and the general public) alternative solutions to their deeply ingrained problems.
Small Part of Brain Itching for a Fight - Science News