New brain scans reveal the mechanisms of task-switching

By: DEANNA CHIECO

Posted: 4/30/09

Throughout an average day at Hopkins, a student needs to switch between many different tasks. Students switch their attention from a professor to their computer screen, or from completeing a statistics problem set to composing an eight-page essay on World War II. The brain is able to quickly make these shifts in attention to carry out different behaviors.

In a paper published in last month's issue of The Journal of Neuroscience, researchers from the Department of Psychological and Brain Sciences determined the answer to the previously unanswered question of how these attention shifts occur.

Previous to the study, two theories of task-switching existed. The first hypothesized that each part of the brain that controls specific types of behaviors has its own mechanism for transitioning between behaviors of the same type, known as domain-specificity.

On the other hand, it has also been suggested that there is one universal mechanism that allows for cognitive switching in any type of task. The researchers were able to determine that this type of task-switching mechanism, known as domain-independence, is the one responsible for our ability to shift our attention between several different activities.

In order to test these two models, subjects were shown stimuli on a screen while a functional magnetic resonance imaging (fMRI) machine revealed the active areas of the brain.

The research team, led by Stepehn Yantis, a professor in the Psychology department, tested how the brain shifted between different types of number categorization and visuospatial attention.

The letters "L" or "R" cued the subject to attend either to the left or the right of the screen. Other letters then cued the subject to categorize a number, which was displayed on the specified side of the screen, as low versus high or even versus odd. These activities allowed the lab to measure which brain regions were active during these task shifts.

In particular, a region called the medial superior parietal lobule (mSPL) was found to be active during the task shifts in both number categorization and spatial attention.

In previous studies, the mSPL has been implicated in cognitive control, but this study is the first to demonstrate that the mSPL controls attention shifts and number categorization shifts when the two types of shifts are being performed simultaneously. Thus, this data suggests a domain-independent mechanism of cognitive control, in which the mSPL is able to initiate shifts in both attention and rule tasks.

However, the domain-specific hypothesis cannot be entirely negated. The Yantis lab observed other specific neural regions within the mSPL whose activity was specific to each type of task. These neuron subpopulations might be part of a preparatory mechanism of task-switching that leads to the subsequent mSPL response.