>> The Frontal Lobes and Cognition

	Interview with Mark D'Esposito, University of California, Berkeley From Studying The Mind, VHS © 2003, W. W. Norton

What do imaging studies reveal about the role of the frontal lobes in cognition?

Researchers have been trying to understand the role of the frontal lobes in cognition for a long time. If we go back 100 years to Phinneas Gage, who suffered a very serious brain injury but seemed fairly normal afterwards, it was unclear as to what specific cognitive deficits resulted from this very big lesion of the frontal cortex. We knew that his behavior had changed, and that people with frontal lobe injuries aren't quite the same as they were before the injury, yet they still perform many tasks normally–for instance, IQ, memory and language abilities seem the same–so trying to capture the frontal lobe's role in cognition has been difficult.

About thirty years ago, when scientists started performing electrophysiological studies and recording from individual neurons in awake behaving monkeys, there was this great discovery that there were neurons that seemed to fire whenever the monkey was holding onto information over a short period of time. Monkeys were given something to remember, and they had to recall it three or four seconds later; during the time that they were remembering the information these neurons would turn on and then they'd turn off. This was a really interesting finding because the neuron was firing to a stimulus that wasn't there, which is the neural correlate of a memory representation.

It was postulated that this part of the frontal lobe was probably important for holding information online. And as you can imagine, holding information online is a basic building block for almost every cognitive ability and almost everything we do. Whether we're trying to comprehend something we've read or heard, or trying to solve a problem, we need to hold some information online as we juggle information and perform other sorts of computations. This discovery led to the insight that the lateral prefrontal cortex may play a very important role for maintaining information online.

In my work I've been trying to understand whether the lateral portions of the human prefrontal cortex also play a role in maintaining information online. And fMRI has been an excellent tool for answering that question because we can do the same type of experiment. We can ask subjects to remember information over short periods of time and scan them and precisely see how the lateral prefrontal cortex responds to holding information. And as it turns out, just as in monkeys, the human prefrontal cortex plays a very important role in holding onto information.

Where the human studies have gone further is to look beyond simply remembering information to more complex tasks that involve using information, performing operations on information, and manipulating information. Every task you do on a monkey is very difficult to train a monkey to do. It might take six months to train a monkey just to remember one piece of information, but you can train an undergraduate to do that same task within minutes and move on to very complicated tasks. Using these basic tasks we have developed a whole series of paradigms that allow us to understand how we can go from remembering information to manipulating information and then using that information to guide our behavior.

There have been a number of interesting findings about the lateral prefrontal cortex. For instance, it's just not a homogenous area, and it's not subserving just one function. Rather, there seem to be functional subdivisions within the lateral prefrontal cortex that are organized to support different components of working memory. Depending on the different kinds of operations you perform–whether the information is spatial or not spatial, for instance, or whether you just maintain the information or manipulate it–different portions of the prefrontal cortex come online.

How the prefrontal cortex is activated during memory tasks also correlates with how well and how efficiently you do the tasks. For instance, young, healthy college subjects who are very fast at retrieving information from memory activate less prefrontal cortex than those who are slower, even though all subjects were highly accurate. What this suggests is that more efficient processing means less neural response. And that's interesting because if you look across the lifespan, that relationship changes. In older individuals the faster you are the more prefrontal cortex you activate. And that gives us some insight not only on how physiology may change with age but also on what the mechanisms are for remembering information and retrieving that information.