You may not
enjoy the smell of your dirty laundry, but your brain knows and appreciates that it’s yours. A new study reveals a key way we detect our own scent and distinguish that scent from others’.
Smell is a powerful thing. Many species use it to communicate (think dogs sniffing their introductions) or attract mates (the Stickleback fish is a good example of this one). Humans may not be as overtly smell-dependent, but our brains actually use this sense more than you might think.
Communication by smell comes down to a thing called the major histocompatibility complex, or MHC. Every creature with a backbone has MHC molecules on the surface of its cells. These molecules act like bouncers, carefully controlling the balance of proteins inside the cell. When new proteins come a-knocking, the MHC checks their IDs to determine if they are okay to enter the cell (recognized as self) or get kicked out (non-self). This keeps the riffraff at bay, but can also cause the body to reject unrecognized things like transplanted organs.
What’s the News: One of memory’s big jobs is to keep straight what actually happened versus what we imagined: whether we said something out loud or to ourselves, whether we locked the door behind us or just thought about locking the door. That ability, a new study found, is linked to the presence of a small fold in the front of the brain, which some people have and others don’t—a finding that could help researchers better understand not only healthy memory, but disorders like schizophrenia in which the line between the real and the imagined is blurred.
Scans of a brain with a distinctive paracingulate sulcus (left, marked by arrow) and without one (right)
What’s the News: The best way doctors have to find out how much pain a patient’s in is to ask—but that approach can fall short when someone’s unable to speak, exaggerating or downplaying their condition, or just plain unsure how to rate their pain on a 10-point scale. Because of these problems with self-reporting, scientists have long been looking for an objective, physiological measure to quantify pain. A recent brain scanning study, in which the researchers could pick out painful experiences based on neural activity, brings that goal closer.
What’s the News: A number of recent studies have suggested that brain scans could be used to diagnose autism. Virginia Hughes investigated these claims in a report for the Simons Foundation Autism Research Initiative. While some researchers feel these tests could soon be ready for the clinic, she found, others feel that relying on the scans for diagnosis is at least premature, and perhaps entirely misguided. Some important points in her report:
How the Would-Be Autism Tests Work:
Large amygdalas, it seems, are social amygdalas.
These paired regions, typically referred to as almond-shaped (indeed their name comes from the Greek for almond), are known to be part of the brain responsible for sociability as well as fear and other deep-seated emotions. Lisa Feldman Barrett and colleagues sought to find out whether size matters in the amygdala, and according to their study in Nature Neuroscience, there is a connection between people having big amygdalas and having big, complex social networks.
The researchers measured two social network factors in 58 adults. First, they calculated the size of a participant’s network, which is simply the total number of people that are in regular contact with the participant. Second, they measured the network’s complexity, based on how many different groups a participant’s contacts can be divided into. … Linear regression revealed a positive correlation in amygdala size with both social network size and complexity. [Ars Technica]
The team’s MRI scans found a wide variation in amygdala size, from about 2.5 cubic millimeters to more than five. But other factors like a person’s happiness didn’t match up with amygdala size. And the subjects’ hippocampus, which the scientists used as a control, showed no variation when compared to a person’s social network. Only the amygdala size showed the connection, Barrett says.
Step 1: Put study subject in MRI machine. Step 2: Show subject video of a huge, hairy tarantula creeping toward their toes. Step 3: Watch panic light up in the brain.
For a study out in this week’s Proceedings of the National Academy of Sciences, Dean Mobbs and colleagues put their subjects through this fright fest to sort out how the brain responds to different parts of a threat. It’s not all about the presence of a creepy crawler, Mobbs found—it’s whether that creepy crawler is creeping closer.
As the spider advanced, MRI scans allowed researchers to see flashes of activity switch from the volunteer’s prefrontal cortex – a region associated with anxiety – to a spot in the midbrain known to involve intense fear. But the neural terror waned when the tarantula retreated, “regardless of the spider’s absolute proximity,” wrote the study’s authors. In other words, as long as the spider was moving away, no matter how close it still was, the volunteers relaxed. [MSNBC]
Your pencil marks on the door frame mark your kids’ ascending height; your photo albums carry the visual record of their ascending ages. Scientists have figured out a new way to track growing up: studying the normal evolution of connections between parts of the brain as a person ages toward adulthood. If advanced far enough, such a method could even help to catch developmental disability.
In a study out this week in Science, the team led by Nico Dosenbach outline the technique based on functional connectivity MRI, or fcMRI. Where the MRI scans we cover more frequently typically reveal brain structure or activity in a particular region, fcMRI focuses on the connections across the brain.
The research team scanned the brains … of 238 normally developing subjects aged 7 to 30, for five minutes. By comparing 200 of 12,720 key functional brain connections and assessing them through multivariate pattern analysis, researchers then predicted volunteer subjects’ developmental status. [Scientific American]
Not just yet.
The day probably will come when functional MRI brain scans become viable evidence in American courts, but thanks to a ruling in a Brooklyn case this week, that day is yet to come.
DISCOVER covered the details of the case two weeks ago—a woman sued her former employer claiming she was treated poorly after complaining of sexual harassment, and wanted fMRI scans admitted as evidence to validate the credibility of a witness. But Judge Robert H. Miller has now denied the request under New York State’s Frye test, which says, among other things, that expert testimony is only admissible if it’s widely accepted in the scientific community. As we saw yesterday when we covered the optogenetics tests designed to verify fMRI results, there are still lingering doubts about the technique’s reliability.
After a quarter-million scientific papers, you’d better hope your methodology was solid.
Most of the studies you’ve probably heard of that try to tie a specific region of the brain to an action or feeling probably relied on a functional MRI technique that tracks the flow of oxygenated blood–so when you see a region “light up” on an fMRI image, that’s not the fMRI picking up the actual neurons firing. Rather, it watches for small changes in blood oxygen levels in the region. This method, called blood oxygenation level-dependence (BOLD), presumes that active neurons use more energy and thus require more oxygen. Now, in a study in Nature, researchers at Stanford Medical Center have provided direct evidence that the inference is correct.
Lead researcher Karl Deisseroth employed a technique called optogenetics to prove the point. He and his colleagues engineered brain cells that respond to a flash of blue light; when they did this trick on cells in the motor cortex of rats, the flash of light acted as a trigger to active the neurons there. The idea was that they would examine these rats with fMRI at the same time they stimulated those motor neurons with the blue light. If the fMRI lit up in the same places where the researchers knew they were stimulating neurons, they could be confident that fMRI was really picking up brain activation.
Sure enough, when the neurons were turned on with a pulse of blue light, the researchers detected a strong BOLD signal emanating from the motor cortex neurons’ neighborhood. The BOLD signals were exactly what was expected. “It was very compelling and reassuring,” Deisseroth says. “Everyone can breathe a sigh of relief” [Science News].
Eleanor Maguire can’t read your mind. But she’s getting closer.
Two years ago the neuroscientist’s team used functional MRI scans of the brain to predict where in a virtual reality environment a person was “standing” just by looking at their brain activity. And now, in a study for Current Biology, she’s used fMRI scans, interpreted by a computer algorithm, to pick out the patterns of brain activity that indicate whether a person is remembering one movie versus another.
An fMRI scan measures the brain’s blood flow—associated with neuron activity—on the scale of voxels, three-dimensional “pixels” that each include roughly 10,000 neurons. The algorithm then interprets the changes voxel by voxel to learn the brain’s patterns of activity over time [ScienceNOW]. In this experiment, Maguire’s team showed their 10 participants three different movies. Each was short, only about seven seconds, but featured a different actress doing a different simple activity, like mailing a letter or drinking coffee. The scientists then asked the subjects remember the films while the team scanned their brains.