One of the biggest puzzles in neuroscience is how our brains encode thoughts, such as perceptions and memories, at the cellular level. Some evidence suggests that ensembles of neurons represent each unique piece of information, but no one knows just what these ensembles look like, or how they form.
A new study from researchers at MIT and Boston University (BU) sheds light on how neural ensembles form thoughts and support the flexibility to change one's mind. The research team, led by Earl Miller, the Picower Professor of Neuroscience at MIT, identified groups of neurons that encode specific behavioral rules by oscillating in synchrony with each other.
The results suggest that the nature of conscious thought may be rhythmic, according to the researchers, who published their findings in the Nov. 21 issue of Neuron.
"As we talk, thoughts float in and out of our heads. Those are all ensembles forming and then reconfiguring to something else. It's been a mystery how the brain does this," says Miller, who is also a member of MIT's Picower Institute for Learning and Memory. "That's the fundamental problem that we're talking about — the very nature of thought itself."
Rules for behavior
The researchers identified two neural ensembles in the brains of monkeys trained to respond to objects based on either their color or orientation. This task requires cognitive flexibility — the ability to switch between two distinct sets of rules for behavior.
"Effectively what they're doing is focusing on some parts of information in the world and ignoring others. Which behavior they're doing depends on the context," says Tim Buschman, an MIT postdoc and one of the lead authors of the paper.
As the animals switched between tasks, the researchers measured the brain waves produced in different locations throughout the prefrontal cortex, where most planning and thought takes place. Those waves are generated by rhythmic fluctuations of neurons' electrical activity.
When the animals responded to objects based on orientation, the researchers found that certain neurons oscillated at high frequencies that produce so-called beta waves. When color was the required rule, a different ensemble of neurons oscillated in the beta frequency. Some neurons overlapped, belonging to more than one group, but each ensemble had its own distinctive pattern.
Interestingly, the researchers also saw oscillations in the low-frequency alpha range among neurons that make up the orientation rule ensemble, but only when the color rule was being applied. The researchers believe that the alpha waves, which have been associated with suppression of brain activity, help to quiet the neurons that trigger the orientation rule.
"What this suggests is that orientation was dominant, and color was weaker. The brain was throwing this blast of alpha at the orientation ensemble to shut it up, so the animal could use the weaker ensemble," Miller says.
Eric Denovellis, a graduate student at Boston University, is also a lead author of the paper. Other authors are Cinira Diogo, a former Picower Institute postdoc, and Daniel Bullock, a professor of cognitive and neural systems at BU.
Oscillation as consciousness
The researchers are now trying to figure out how these neural ensembles coordinate their activity as the brain switches back and forth between different rules, or thoughts. Some neuroscientists have theorized that deeper brain structures, such as the thalamus, handle this coordination, but no one knows for sure, Miller says. "It's one of the biggest mysteries of cognition, what controls your thoughts," he says.
This work could also help unravel the neural basis of consciousness.
"The most fundamental characteristic of consciousness is its limited capacity. You only can hold a very few thoughts in mind simultaneously," Miller says. These oscillations may explain why that is: Previous studies have shown that when an animal is holding two thoughts in mind, two different ensembles oscillate in beta frequencies, out of phase with one another.
"That immediately suggests why there's a limited capacity to consciousness: Only so many balls can be kept in the air at the same time, only a limited amount of information can fit into one oscillatory cycle," Miller says. Disruptions of these oscillations may be involved in neurological disorders such as schizophrenia; studies have shown that patients with schizophrenia have reduced beta oscillations.
Massachusetts Institute of Technology: http://web.mit.edu/newsoffice
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
Pigs ‘edited’ with a warthog gene to resist African swine fever could help spawn GM animal farms in the UK
Mouse House to make naturalist biopic, six years after box-office failure of Creation, starring Paul Bettany
International team spends 10 years making inroads into treatment of bacterium which kills up to half of those it infects
You may not know it, but you probably have some Neanderthal in you. For people around the world, except sub-Saharan Africans, about 1 to 3 percent of their DNA comes from Neanderthals, our close cousins who disappeared roughly 39,000 years ago.
Research at Yale plotted what happened in the brains of two scientists as they held a conversation
From medicines to jet fuel, we have so many reasons to celebrate the microbes we live with every day
Genome sequencing indicates Kennewick Man is Native American, reopening the bitter battle over whether he should be reburied or studied
In the article on the discovery of dinosaurs (They’re back, Review, 6 June) you state: “In Sussex, a local doctor uncovered fragmentary remains of what appeared to be two more species of colossal extinct land reptiles.” You grossly underplay the contribution of Lewes-born Gideon Mantell, geologist and palaeontologist, author and diarist, friend to princes and international scholars as well as local doctor. Mantell not only discovered (aided by his wife) the first remains of the iguanodon in 1824 but named it – as it resembled the tooth of an iguana. This was the first known land dinosaur, Mary Anning having identified the first sea-living dinosaur.Mantell went on to put together more pieces of the jigsaw with extra fossil discoveries. In contrast to Richard Owen, whose models form the basis for the Crystal Palace dinosaurs, Mantell stated correctly that iguanodon would have walked on their back legs, using their forearms to fight or gather food. He did, however, attribute the thumb spike to a nose horn though later corrected this assumption. The Natural History Museum has a display on Gideon and his wife Mary’s contribution as well as the large “Mantell-piece” of Iguanodon fossils that he had on show in his museum in Brighton. He sold it, along with many more priceless items, to the British Museum in 1838. Gideon Mantell’s reputation deserves better than your throwaway remark. Debby MatthewsLewes, East Sussex Continue reading...
Unique triangular hairs help keep Saharan silver ants cool at 70°C by manipulating the physics of light
Most animals wouldn't confront a fearsome predator like a lion. But through sophisticated group work, hyenas launch successful raids