How the brain assigns objects to categories

How the brain assigns objects to categories
New research from MIT neuroscientists suggests how the brain learns which category an object belongs to — for example, fruits or animals. Image: Christine Daniloff

The human brain is adept at recognizing similar items and placing them into categories — for example, dog versus cat, or chair versus table. In a new study, MIT neuroscientists have identified the brain activity that appears to control this skill.

The findings, published in the July 27 issue of the journal Neuron, suggest a potential explanation for why autistic children focus intently on details, but often seem unable to group things into broad categories, says Earl Miller, the Picower Professor of Neuroscience and senior author of the paper.

"We think what may happen in autism is the system may get out of balance … and as a result, the details overwhelm the category. Then you have a that's not only too good at memorizing details, it can't help but memorize the details," says Miller, a principal investigator at the Picower Institute for Learning and Memory at MIT.

Miller and Picower postdoc Evan Antzoulatos focused their study on two brain regions, the prefrontal cortex and the striatum, which is part of a larger structure known as the basal ganglia. Both regions are known to be important for learning.

Until a few years ago, it was believed that the prefrontal cortex learns information quickly, then sends what it learns to the basal ganglia, which helps form habits, such as the ability to play a musical instrument. However, in 2005, Miller and colleagues showed that when monkeys learn simple tasks, their basal ganglia are more active early in the process, followed by a slower activation in the prefrontal cortex.

In other words, the striatum quickly learns the individual puzzle pieces, and the prefrontal cortex puts them together, Miller says. He and Antzoulatos theorized that the same pattern would be evident during category learning.

For the new Neuron study, Antzoulatos trained monkeys to assign patterns of dots into one of two categories. At first, the animals would see only two examples, or "exemplars," from each category — a small enough number that they could memorize the category to which each belonged, without having to learn the general category traits. After the animals learned the first two exemplars, the number would be doubled. Eventually, the number of exemplars became so great that it was impossible to memorize them, and the monkeys' brains would start picking up on general traits that characterize each category.

As they did so, brain activity shifted from the striatum, a more primitive brain region, to the prefrontal cortex, which is responsible for high-level functions such as planning and decision making.

"What happens during category learning is the more primitive, faster can memorize the exemplars, but then it sends what it learns up to the prefrontal cortex. And the prefrontal cortex figures out what's common among all the exemplars, among all the individuals, and extracts the essence," Miller says.

Gregory Ashby, a professor of psychology at the University of California at Santa Barbara, says the new study represents the "clearest picture yet" of the striatum's involvement in category learning. "We've known for quite a while that the striatum plays an important role in category learning, but it was not at all clear exactly what that role was," he says.

In future studies, the MIT researchers hope to test their theory that autism results from an imbalance between the striatum and prefrontal by interfering with the normal balance between the two brain regions and observing the results.

Related Stories

Why we learn more from our successes than our failures

Jul 29, 2009

( -- If you've ever felt doomed to repeat your mistakes, researchers at MIT's Picower Institute for Learning and Memory may have explained why: Brain cells may only learn from experience when we ...

Unconscious learning uses old parts of the brain

Apr 06, 2010

( -- A new study from the Swedish medical university Karolinska Institutet provides evidence that basic human learning systems use areas of the brain that also exist in the most primitive vertebrates, such as ...

Recommended for you

Know the brain, and its axons, by the clothes they wear

12 hours ago

(Medical Xpress)—It is widely know that the grey matter of the brain is grey because it is dense with cell bodies and capillaries. The white matter is almost entirely composed of lipid-based myelin, but ...

Turning off depression in the brain

Apr 17, 2014

Scientists have traced vulnerability to depression-like behaviors in mice to out-of-balance electrical activity inside neurons of the brain's reward circuit and experimentally reversed it – but there's ...

Rapid whole-brain imaging with single cell resolution

Apr 17, 2014

A major challenge of systems biology is understanding how phenomena at the cellular scale correlate with activity at the organism level. A concerted effort has been made especially in the brain, as scientists are aiming to ...

User comments

Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (2) Jul 28, 2011
This is phenomenal. It takes us just a little bit closer to understanding what is cognitively exceptional in our fellow primates, and ourselves. It seems evolution has vindicated the utility of ontological distinctions.
not rated yet Jul 28, 2011
"It seems evolution has vindicated the utility of ontological distinctions." - Gp

O.k. I am going to put everything into one category.
You know, a simple thought for a simple mind:

Nature is exceptional.

Phenomenon, understanding, cognition, primates, ourselves, evolution, vindication, utilities, ontology, and distinctions I will leave to you.

Why five stars? (Your statements sound music.)

Fourteen times. The colleagues used the various tenses of the word "learn" fourteen times!

That's a lot. For a word that enjoys no universal definition.
not rated yet Jul 28, 2011
*brains would start picking up on general traits that characterize each category*
It is very difficult to program the common features or general traits, because there is always plenty of exceptions.
not rated yet Jul 29, 2011
@droid001. Very true. That question of how the brain picks up and sorts general features is an even bigger one.

@hush1, your point about learning is well made. And this matter of what learning really IS will hopefully be resolved someday by discoveries such as these.
not rated yet Jul 29, 2011

"Even before language, babies learn the world through sounds"


The researchers and their work can not be stress or emphasized enough for their contribution to the understanding of learning.

This research team comes closest to a universal definition of the word 'learn'.

to learn: learning; exploitation of internal and external physical processes within the resolution and sensitivity range of all biological activity able to exploit any physical phenomenon.

In other words, any sensory mode any life form is capable of can NOT be nonphysical in nature.

Furthermore, all chemical biological physical processes for learning are mutual physical interactions.

Chromsky was right. Language is structure. And the origin to this structure as well as to ALL human language is physical. The basis and nature of learning is physical. For life as we know it.

There is no psychology of learning. At this level of learning.
not rated yet Jul 31, 2011
Categories are funny things. Maybe babies and photo albums should be in the same category because people tend to grab both if there is a fire. Dogs and cats are both in the same category and in different categories depending on context (animals vs species) etc.