Toronto, CANADA -- A new study has found the strongest evidence yet that what sets humans apart from other primates may be found in the brain's frontal lobes, particularly in an area the size of a "billiard ball" called the right prefrontal cortex.
Dr. Donald Stuss, one of the world's experts on the frontal lobes, led the study at The Rotman Research Institute, part of Baycrest Centre for Geriatric Care, and affiliated with the University of Toronto. The findings are published in the February 2001 issue of the international journal BRAIN and the subject of the lead editorial.
Understanding the mental processes of others -- mentalizing -- is the basis of our socialization and what makes us human. It gives rise to our capacity to feel empathy, sympathy, understand humor and when others are being ironic, sarcastic or even deceptive. It's a "theory of mind" that has been associated with the frontal lobes, but until now scientists have had difficulty demonstrating this ability to specific regions of the brain.
What is exciting about this study, according to Dr. Timothy Shallice of the Institute of Cognitive Neuroscience at University College London, is that the Rotman study came at this challenge with two different testing methods and both generated similar compelling evidence to show that these higher cognitive functions in humans are "localizable" to a specific region within the frontal lobes. Dr. Shallice wrote the lead editorial in BRAIN.
Dr. Stuss and his research colleagues tested patients who had damage to various parts of the frontal lobes, and other areas of the brain as well. The selective impairment in only some patients provided the ability to precisely localize those regions that are necessary when specific mentalizing tasks are performed. Co-authors on the paper with Dr. Stuss, who is director of The Rotman Research Institute at Baycrest, were Dr. Gordon Gallup, Department of Psychology, State University of New York at Albany; and Dr. Michael Alexander, Memory Disorders Research Centre at Boston University and Department of Neurology, Harvard University.
"In our study, we've shown that the frontal lobes were the most critical region for visual perspective taking, and the inferior medial prefrontal region, particularly for the right, for detecting deception," says Dr. Stuss. Visual perspective taking is the ability to empathize or identify with the experience of another person.
It has long been known that some patients with frontal lobe damage have significantly changed personalities. What is important about the study is that it helps families, friends and caregivers of the patient to appreciate and understand a very important reason why this occurs. This deficit in mentalizing can affect social cognition which is important in everyday human interactions. For example, patients with damage in the specific frontal area are often less empathetic and sympathetic, and they miss social cues which lead to inappropriate judgements.
In the study, 32 adults with lesions in frontal and non-frontal brain regions, most commonly as a result of stroke, and a control group of 14 healthy adults, underwent two seemingly very simple tests. Both tasks required participants to guess which coffee cup a ball was hidden under. Participants sat across a table from the experimenter and a table curtain was used on some occasions to conceal which cup the experimenter hid the ball under. The participant was asked to point to the correct cup.
In the first test -- visual perspective taking -- participants had to reflect on their own experience to understand and interpret the experience of others. For example, the participants either saw the ball being hidden under a particular cup with the curtain open, or were told that the ball was being hidden when the curtain was closed and they could not see anything. Then two assistants joined the task; one sat beside the experimenter, and one beside the participant. The table curtain was drawn this time, concealing which cup the ball was placed under. When the participant had to guess where the ball was hidden, the assistants 'helped' by moving beside the examiner and each pointed to a different cup. Participants needed to realize that one of the assistants had not been in a position to see where the ball was hidden (because they were sitting beside the participant who themselves could not see where the ball was hidden). Frontal lesion subjects had a much higher error rate on the task and it appeared that the 'right' frontal lobe was most critical. While the small number of right frontal subjects (4) makes this only a suggestion, it is still a striking finding, says Dr. Stuss.
In the second test on deception, an assistant sat at the table beside the experimenter and always pointed to a cup where the ball was NOT hidden. Participants had to infer that the assistant was trying to deceive them. Those with right inferior medial prefrontal damage had difficulty catching on to the ruse and were the most frequently deceived.
Funding for the study was provided by the Canadian Institutes of Health Research. Baycrest Centre for Geriatric Care is an academic centre fully affiliated with the University of Toronto. In addition to being director of The Rotman Research Institute, Dr. Stuss is Vice-President of Research at Baycrest and Professor of Medicine (Neurology, Rehabilitation Science) and Psychology at the University of Toronto.