Connections found in brain

Carnegie Mellon University neuroscientist Marcel Just and Stanford postdoctoral fellow Sashank Varma have proposed new principles that explain how the human brain operates when performing complex cognitive tasks, such as language comprehension and spatial reasoning.

Within the field of cognitive science, the accepted belief is that there exists a one-to-one mapping between particular high-level cognitive processes and the activation of a single cortical area. That is, each area of a person’s brain is responsible for a particular cognitive task.

According to Just and Varma’s publication in Cognitive, Affective & Behavioral Neuroscience, this interpretation is incorrect and a “gross oversimplification of a more complex ... many-to-many mapping, governed by more subtle organizational principles.”

Just and Varma propose that the many-to-many mapping involves several cortical areas that are responsible for several cognitive activities.

The two researchers have developed a computational theory of the brain called Capacity Constrained Concurrent Cortical Activation-based Production System (4CAPS). This theory is specifically used to model brain activities of language comprehension, problem solving, spatial reasoning, and dual-tasking.

The 4CAPS theory provides a unique architecture of the brain in that it is the first model that illustrates resource utilization in brain areas that are consistent with fMRI images.

By adjusting capacity constraints, 4CAPS can be used to model brains that are under certain adverse conditions. For instance, researchers can model an autistic brain by decreasing the capacity of bandwidth resources that can be consumed for each task.

“4CAPS is an attempt to take seriously the fact that brain function, and thus cognition, is constrained by resource limitations,” said Varma. “The goal is to see how much of the brain functions can be understood as a consequence of minimizing resource consumption.”

Although there is functional redundancy across cortical areas in the brain, there is typically one area in the brain that is most efficient at a particular task. For example, Broca’s area, a region on the left side of the brain, is most efficient at syntactic analysis. However, if this area is somehow damaged or if the task of syntactic analysis becomes too complex, homologous areas in the right brain become more active.

In a Carnegie Mellon press release, Just likened the brain’s behavior to that of a sports team. In other words, if a forward or quarterback is somehow injured or overworked, there is a ready — albeit less capable — replacement ready to join the fray. In the same way, if an area of the brain malfunctions, the brain has backup regions to perform the necessary function.

In their computational theory of the brain, Just and Varma also explain the limits of cortical areas. Just said that the human brain is a “biological thinking machine with a finite capacity of resources.”

These finite resources may explain the slow and degraded performance of more complicated tasks, such as processing statements with a relatively more complex syntactic structure.

“Oxygen and glucose are, after all, scarce resources in the body,” said Varma, although the relationship between quantity and complexity of a cognitive task and the resources it consumes has yet to be explored.

In their paper, Just and Varma further state that “the topology of a large-scale cortical network changes dynamically during cognition.” This claim rejects the possibility that there is a preordained set of cortical areas that perform a task.

In fact, there is evidence from Just and Varma’s research that the set of cortical areas involved in a cognitive task changes from trial to trial and moment to moment within a single trial.

The most novel of Just and Varma’s proposals is that “the communication infrastructure that supports collaborative processing is also subject to resource constraints.”

In other words, Just and Varma’s research indicates that the brain’s constraint on bandwidth limits the communication between and among activated areas. The difficulty of multitasking might be the result of these limitations. This conclusion has been drawn through experiments involving driving a car coupled with the task of listening.

In these experiments, Just observed that the regions actively engaged in driving would reduce in activity by 40 percent as soon as the task of listening was introduced into the trial.

The importance of Just and Varma’s research is in the novel idea that thinking is performed by a cooperative group of cortical networks that are limited by resource capacities, but these networks can dynamically adapt to changing demands in cognitive activity.

According to Just, “All of humanity is brain activity.”