ARCHIVED - Computing Brain Activity Through Images
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May 05, 2005— Ottawa, Ontario
How EEGs work
Electroencephalography (EEGs) help medical professionals detect and diagnose neurological disorders, such as stroke, coma, cerebral palsy and major brain trauma. By placing electrodes on the scalp, a series of electrical impulses originating in the brain are amplified and summed into waves that can be monitored and analyzed.
Since Dr. Penfield's neuroanatomical mapping of the brain in the 1930s at the Montréal Neurological Institute, Canada's scientists continue to probe the mind and its processes. From science-fiction to future realities, Dr. Lizann Bolinger and Dr Ryan D'Arcy, from the Winnipeg and Halifax NRC Biodiagnostic (NRC-IBD) research facilities respectively, are on a quest that may lead to mind- and thought-controlled computers. Pending that, Drs Bolinger and D'Arcy believe that by combining EEG (Electroencephalography) and fMRI (functional Magnetic Resonance Imaging), it will be possible to improve current diagnosis of neurological conditions, ranging from epilepsy and Alzheimer's disease to Autism or ADHD (attention-deficit hyperactivity disorder).
|Scalp electrodes and EEG electrical activity|
Bolinger and D'Arcy are exploring the more complex and higher level thought processing involved in language and memory. NRC scientists aim to narrow the gap between the spatial precision of fMRIs and the timely precision of EEGs so that neurologists can take advantage of these two complementary brain-imaging technologies.
How fMRI Works
The blood oxygen level dependent fMRI technique takes advantage of the fact that the oxygenation state of red blood cells affects its ferrous magnetic properties. Very active brain regions attract greater blood flow. Scientists compare the differences in blood and oxygen levels flow and levels of brain cell oxygen-retention, between a resting condition and an active condition, to determine and differentiate task-related regions. These findings and differences are processed using software and offer neuroscientists great insight into the working brain.
While EEGs represent a summation of the cerebral electrical activity detected on the scalp, fMRIs monitor brain function in terms of increases and decreases of oxygen in the blood supply. With increased stimulation, blood flows more rapidly to the activated regions of the brain. The increased flow brings more oxygen, which can be detected as a change in signal intensity in fMRI. However oxygen delivery and uptake is an indirect change that requires more time to occur than does the on-going electrical brain activity measured by EEG.
|An fMRI map|
D'Arcy offers the following analogy: "Imagine the brain's anatomy as though it were the ground map of North America with all its mountains, valleys and waterways detailed. Now imagine the highly complex and dynamic weather systems that move across North America – these are similar to studying brain function in many ways. So, combining fMRI and EEG technologies is offering us a better picture of our brain's activity in both time and space."
"Our challenge is to improve the integration of both the fMRI map and EEG recordings for earlier and more precise detection of brain abnormalities." says D'Arcy.
"Working with computer scientists, such as Dr. Yannick Marchand at NRC-IBD Atlantic, we are developing new clinical measures that utilize the complementary advantages of these two functional neuroimaging techniques" adds Bolinger.
|Differences in blood and oxygen levels in the brain shown by fMRI maps|
D'Arcy and Bolinger have taken the already-proven N400 electrically event-related potential (ERP) a step further as they are narrowing the brain region responsible for this electrical rendition of higher thought processing by combining both the N400 ERP and fMRI. Several normal patients have been N400-tested in a clinical setting, D'Arcy and colleagues have now tested neurologically-compromised patients to determine whether their higher cognitive processes enable them to understand their environment, including comments and questions from health professionals, friends and relatives. This team hopes to see a combination of N400 and fMRI become a clinical test for "communication-impaired" patients, so that these patients can regain the respect they merit, as human beings.
Valuing the N400 ERP
Event-related potentials (ERPs) represent isolated and valued information within EEGs, much as a very focused microphone can isolate the noise of the queen bee within a hive. At about 400 milliseconds following our brain's processing of an illogical statement, (e.g. "The pizza is too hot to sing"), we find an ERP which spikes in healthy and otherwise non-compromised areas of the brain related to higher thought processes.
Combining NRC neuro-imaging expertise across Canada from Halifax to Winnipeg, D'Arcy has begun imaging communication-impaired patients and integrating EEG and fMRI, while Bolinger is refining fMRI mapping techniques and clinical applications, so that an interface between the brain's activity and computers can be developed. NRC researchers are narrowing the gaps between mind and matter. As we grow closer to understanding the brain, we can envision applications for the combination of these two technologies; amongst them: medical, forensic, and safety applications.
In Germany, patients with Lou Gehrig's disease are being trained to use their brain waves to interact with the outside world. In Israel, the alertness of fighter pilots is being monitored to improve safety during extended flights... D'Arcy emphasizes the medical applications, which have begun to awaken interest in a wide range of clinicians involved in treating neurological disorders and diseases. These NRC scientists believe that the honing the ability of EEGs and fMRI to tell us more about brain function will lead to earlier diagnosis and treatment of neurological and psychiatry conditions. Hopefully, NRC's technical strengths in this area of research will also contribute to future developments in brain-computer interfaces whereby thoughts could trigger computer functions and communications, offering much hope and enhanced quality of life for patients and their loved ones.
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