We tend to think in categories. It streamlines our ability to think about much of what we encounter. And now scientists have begun to pinpoint just where this kind of categorizing of different types of information such as animals, cars and food groups takes place in the brain.

Researchers have discovered that the posterior parietal cortex, a region of the brain thought to be involved in basic visual processing, is very strongly involved in the complex task of categorizing specific signals – much as a baseball umpire does while calling balls and strikes.

'The number of decisions we make per minute is remarkable. Understanding that process from a basic physiological perspective is bound to lead to ways to improve the process and to help people make better decisions.'

The study demonstrated that monkeys use the posterior parietal cortex in a computerized task in which they determined the category of a moving visual stimulus. In this task, the posterior parietal cortex was used a lot more than the prefrontal cortex – the latter of which is typically associated with higher level cognitive functions.

The investigators trained monkeys to perform a relatively simple game in which they categorized dots moving in different directions into one of two categories. The monkeys were able to either hold on to or release a joystick while they processed in their brains whether the dots belonged in the same or different category.

While the animals performed the task, the researchers, based at the University of Chicago, recorded the monkeys’ neural activity simultaneously in two separate areas – the lateral intraparietal area (LIP) of the parietal cortex and the prefrontal cortex. While both regions experienced changes in neural activity while the animals performed the task, the LIP changed much stronger and faster than the prefrontal cortex.

The LIP also responded much stronger when the animals were given a second task in which they attempted to categorized two sets of ambiguous dots – ones that did not belong in category one or category two.

Since the changes in neural activity occurred in the LIP before the prefrontal cortex, the investigators believe that the parietal cortex is more involved in the visual categorization process, and may be the area in which visual categorization first originates.

The researchers, based at the University of Chicago, also believe that the neural activity from the posterior parietal cortex does not only correlate with the monkeys’ activity, but can predict ahead of time which category the monkey will choose. The investigators accomplished this by analyzing in detail the how the patterns of neural activity deviated from one another as the animal decided between the two categories. Predicting behavior was an area thought to be encoded by the prefrontal cortex, but it now appears that the parietal cortex can predict behavior as well.

"The number of decisions we make per minute is remarkable," said lead author David Freedman, assistant professor of neurobiology at University of Chicago. "Understanding that process from a basic physiological perspective is bound to lead to ways to improve the process and to help people make better decisions. This is particularly important for patients suffering from neurological illnesses, brain injuries or mental illness that affect decision making."

The study was published online in the journal Nature Neuroscience.