Day 2: Big day. Tweets will have covered most of this. While “SfN” has been “cracking down” on the livetweeting, apparently the big talks are ok. All the other talks, you have to wait a whole fifteen minutes til it ends. We’ll live. On with the show:
Never trifle with a multisensory perceptron when experience-dependent plasticity is on the line
Thanks to the booze rooster, I was up and at ’em at 8 am checking out a session on the cerebellar theory of autism. Sam Wang from Princeton ran the session and gave a standout talk. I should mention before diving in that this is the same Sam Wang whose election forecast models beat Nate Silver’s in the 2012 presidential election.
But that’s neither here nor there. Wang is also a neuroscientist, and a big proponent of the idea that autism is the result of dysfunction in the cerebellum. People with autism spectrum disorder consistently have abnormalities here, but there’s a paradox: If adults get an injury here they end up with an impaired ability to move, not autism. So Wang proposed that the damage must occur during what is known as a sensitive period to result in autism. This process he likened to the superfamous sensory deprivation experiments by Hubel & Wiesel, in which they sutured the eye of a young cat shut and saw that the deprived visual cortex failed to wire up properly. This only happened during a certain window of the cat’s early life, which told them that for normal function, the visual system requires stimulation in that window and once it’s passed, it’s too late.
Wang argued that, because the cerebellum acts as a neuronal machine for multisensory learning, if it sustains an injury early in life then all of the areas it connects to will fail to wire up properly. Because this doesn’t happen for adults with cerebellar injury, this means the cerebellum plays a special role in wiring up the brain during development. The association cortex, where sensory information is built up into more high-concept information, is deprived of the cerebellar guidance it needs. This lack of sensory convergence in the brain could explain some characteristics of autism spectrum disorders.
Poster: Choking under pressure
I visited Taraz Lee and Scott Grafton’s poster on choking under pressure. Taraz carefully designed a study where people could receive 5, 10, or 40 dollars for completing a difficult motor task correctly. At the end of the experiment, he chose one trial at random for their payout, meaning it behooved them to bank a bunch of $40 trials. The $40 trials were kept rare to drive up the pressure, and people choked more often on them than on the $5 or $10 trials.
They used functional magnetic resonance imaging (fMRI) to scan their brains as they completed the task. In their recent paper, they found that the people who ended up choking less on these trials also had greater connectivity between their thinky, task-oriented, rule-loving dorsolateral prefrontal cortex (dlPFC) and their action-generating primary motor cortex (M1). “Connectivity,” of course, meaning their slow changes in blood flow tended to change in tandem.
In their current study, they used transcranial magnetic stimulation (TMS) to disrupt activity in the dlPFC. This increased the sensitivity to monetary pressure in a bunch of brain regions, causing others to compensate. TMS also turned “champions” (people who did better under monetary pressure) into “chokers.” Currently, Taraz & Scott need more data to see if this emerging pattern holds, but I like to think of the dlPFC as bracing and tightening and focusing as hard as it can on M1 the way a gymnast tries to summon laserlike focus on a balance beam. I sometimes anthropomorphize brain regions.
New Hero: Mahzarin Banaji
Banaji’s talk explored how we form in-group biases. Newborn babies will mimic facial expressions–we’re like Krazy Glue when it comes to picking up the expressions and habits of those around us. That’s how we charm our caregivers as babies, and we keep on doing it because someday this is how they will know to take care of us. We’re like them.
Discrimination, she said, isn’t as much about excluding people not like you as it is about giving preference to people like you. Really what we need is a diversity of perspectives. Next time you interview assistants, grad students, whoever–try to be just a little bit open-minded, and you’ll end up rich in the perspective that uptalking weirdo you hired brings. Geniuses aren’t always easy to spot in a crowd.
This applies to all kinds of intergroup behavior, and as it turns out, we are total idiots when it comes to deciding who’s good, who’s competent, who to trust. Simply decreasing the distance between a person’s eyes, studies have shown, will make complete strangers judge a face as dumber. These judgments come out of nowhere–what does it even MEAN, she asked, to say someone has an “honest smile”? And yet, the facial features that cause people to be viewed as “more competent” have predicted the margin of victory in every presidential election. There is no reason to think these heuristics are real or useful, and yet there they are, their fingerprints all over our minds whether we like it or not.
Tom Jessell: You are nothing without your vestibular system
Motor learning people like to start off their talks by saying something like “The human brain is for producing movement.” We say this because people studying all the fancy stuff like thoughts and feelings and the fun tricks that differentiate us from the animals, well, they tend to get most of the attention, and we have a bit of a chip on our shoulder about it. Movement is freaking amazing, ok? Just because your dog can do it doesn’t make it a dumb trick.
So anyway I don’t know if he meant to bait and switch, but it was pretty great. Try all you want to produce movement without a good solid vestibular system, but you won’t get very far. This system is a set of fluid-filled canals just beyond the eardrum that helps us balance and generally keep track of our body position in space. This information gets sent to neurons in the spinal cord responsible for twitching the muscle fibers to make us move. Jessell first pointed out that without inhibition from interneurons using the neurotransmitter GABA, wildly oscillating movements result. That is because this inhibition tells the motor neurons when to listen to the feedback and adjust for it and when to just keep on going with the smooth movement. When they administered diptheria toxin to mice to selectively destroy this inhibition, their movements became corkscrewy and hopelessly off-course.
He then talked about how normally, our extensor and flexor muscles work in alternation. Whether bending your knee to walk or flexing a bicep for an admirer, the muscle on one side of the limb is stretched while the other one can go more slack. However, when you, say, fall or lose your balance, they contract at the same time. By playing around with the inhibitory interneurons, altering the function of the pumps that maintain disequilibrium of chloride ions inside and outside the cell, they can switch the inhibition to excitation. They could manipulate the switch from alternation to co-contraction of muscles, and the result was…ok. Imagine if your fingers were so tightly outstretched, your toes too, that if you crawled around you were teetering atop your flexing, rigid fingers. Ballet-style en pointe, on your fingers. Watching a rodent do this was unsettling and weird and it made me deeply appreciate my vestibular sense and its amazing inhibitory interneurons.
That’s all for today, nerds. I don’t know why I’m still up, except for oh wait, it’s DC, so of course there is a pack of feral 22-year-olds above us doing superloud youthful things. Ugh. I hope they lose their vestibular senses so they collapse in a heap and this infernal pounding stops.