Humans are social beings and as such one of our crucial abilities is to successfully tell a large number of faces apart, even though they might be very similar in appearance. This ability is reflected in a finding reported in last week’s edition of The Journal of Neuroscience where researchers identified two brain regions, each the size of a 20-cent coin, whose function is to help process the unique features of faces. Thanks to the use of two different brain imaging techniques, and the cooperation of Ron Blackwell, a 47-year old engineer from California suffering from epilepsy, the researchers were for the first time able to show how these regions contribute to how we perceive faces. This finding might have important implications for people that suffer from so-called ‘face blindness’, an inability to perceive faces but not other types of objects, estimated to affect 2% of the population*.
The fusiform gyrus is an area lying in the outer layer of the brain, just behind the ear, and has been known to be involved in how we distinguish the visual representation of objects, words, and faces. The recent study by Dr. Josef Parvizi, an associate professor of neurology at Stanford University, and colleagues used two different ways of measuring brain activity which enabled them to verify that the pinpointed locations only responded to faces and not other types of visual features. The researchers recruited the help of patient Ron Blackwell who suffers from a severe form of epilepsy and was about to undergo a surgical procedure to remove the brain tissue from where the seizures originate. Before these types of operations the patients are fitted with electrodes on top of their brains in order to measure exactly where the epileptic activity stems from and to perform something called functional mapping where a series of tests are run and analyzed together with data collected from the patient´s brain. This is done to ensure that crucial functions like speech and movement will not be affected if the decision is made to remove small parts of the brain.
In addition to measuring brain activity, doctors can also induce current through the electrodes and thereby activate areas of the brain that lie directly beneath. This stimulation is neither painful nor harmful and can tell us a lot about what the targeted regions do. When Ron was instructed to watch Dr. Parvizi’s face at the same time as the two areas were stimulated, he reported that as the stimulation started the doctor’s face just changed, ‘metamorphosed’, and was unrecognizable. Over several trials that constituted real and fake stimulation in order to make sure that what Ron actually experienced was due to the stimulation, Ron reported the same phenomenon of the faces of the people he was watching suddenly changing from their usual appearance.
This study is of interest to researchers and doctors treating patients with prosopagnosia, or face blindness, a severe deficit that can be inherited or follow brain damage. Prosopagnosia has been linked to abnormal functioning in (or damage to) the fusiform gyrus and was brought much attention through neurologist and author Oliver Sacks’ novel The man who mistook his wife for a hat. Sacks himself suffer from an inherited form of prosopagnosia along with famous American painter Chuck Close who uses voices and postures to identify the persons he is talking to but loses their identity as soon as they move, they then become unfamiliar.
Source: Cosmos Magazine
Video of Ron Blackwell undergoing electrical stimulation of the fusiform gyrus: available here
References: Parvizi, J., Jacques, C., Foster, B., Withoft, N., Rangarajan, V., Weiner, K., & Grill-Spector, K. (2012). Electrical Stimulation of Human Fusiform Face-Selective Regions Distorts Face Perception Journal of Neuroscience, 32 (43), 14915-14920 DOI: 10.1523/JNEUROSCI.2609-12.2012
Grüter, T., Grüter, M., & Carbon, C. (2008). Neural and genetic foundations of face recognition and prosopagnosia Journal of Neuropsychology, 2 (1), 79-97 DOI: 10.1348/174866407X231001