London, November 10 : An international team of researchers has found that simple decision-making tasks do not involve the brain's frontal lobes, where many of the higher aspects of human cognition like self-awareness are thought to originate.
The team led by scientists from Washington University School of Medicine in St. Louis and Italy's University of Chieti instead says that the regions that decide are the same brain regions that receive stimuli relevant to the decision and control the body's response to it.
While the same principle has been shown in primates, some researchers still believe that the brain has a general decision-making module that involves the frontal lobe independently of the neural systems for perception and action.
"It is important to understand how the brain makes decisions under normal conditions to gain insight into diseases like Alzheimer's disease, traumatic brain injury or stroke in which decision-making is disrupted," Nature Neuroscience quoted senior author Dr. Maurizio Corbetta, the Norman J. Stupp Professor of Neurology, as saying.
"We like to think of our decisions as wilful acts, but that may be an illusion. Many decisions may be much more directly and automatically driven by what our brain is sensing," Corbetta said.
For their study, the researchers trained volunteers to perform a task that involved discriminating between an image of a face and an image of a building. Varying degrees of noise obscured the image during the brief time it was visible.
The researchers asked the study subjects to indicate which type of image they believed they had seen-by either moving their eyes in a particular direction if they had seen a face, or pointing their hand in the same direction if they had seen a building.
"This decision is not automatic. It requires both attention to the stimuli and control of the response," Corbetta says.
The researchers took functional magnetic resonance imaging scans of subjects' brains as they performed the task.
They revealed that to help distinguish between the influx of sensory information and the decision to move the eye or hand, they had asked the participants to wait for 10 seconds after seeing the image before indicating which type it was.
Focusing on the regions of the brain that are responsible for planning actions in the parietal lobe, the researchers observed that activity in the different regions would increase in correspondence with the type of stimulus a subject was being shown (face or building), and the type of response they were planning as a result (eye or hand movement).
The researchers said that brain activity levels in the appropriate area rose when the stimulus had less noise, and the subjects were more confident in their choices.
According to them, such regions showed activity that related to the choice even when the stimulus was ambiguous.
"This suggests that these regions in the parietal lobe processed all the sensory, decision and motor signals necessary to make and act on the decision. In contrast, no area in the frontal lobe, thought to be involved in decision-making, significantly increased its activity at the time of decision," says lead author Annalisa Tosoni, a graduate student at the University of Chieti.
Corbetta says that the frontal lobes could have been involved during the training period that preceded the scans, and that those areas might have delegated responsibility for the decision to premotor brain regions as the volunteers learned the task.
However, adds the researcher, the frontal lobes became silent once the participants learnt the task.
"Even for arbitrary and somehow complex visual decisions, it seems to be purely a matter of the amount of sensory information pushing the brain toward one choice or another " he says.
The researcher are currently planning further studies to determine whether more complicated decisions are carried out by this relatively simple sensory-motor mechanism, and how decisions are affected by the amount of reward the subject expects when performing simple and complex decisions.