The development of powerful new imaging methods has transformed neuroscience over the past few decades. Thanks to these remarkable advances, we can now watch the human brain in action as volunteer subjects perform tasks involving language, emotion, memory, even self-reflection -- allowing us to see with unprecedented detail which parts of the brain underlie these different aspects of our mental lives.
In addition to revealing normal brain function, neuroimaging is providing new views of brain disease. It allows us to see, for example, how the brain’s memory systems are affected by Alzheimer’s disease; how emotional responses are altered in depression; or how language processing is affected in people with dyslexia. Through studies such as these, researchers are gaining new insights into the causes of disease as well as new ways to monitor the effectiveness of potential treatments.
The Martinos Imaging Center at MIT uses several different brain imaging methods, each of which has its own advantages and disadvantages.The most detailed views of brain activity are often obtained by combining different methods in a single study.
Magnetic Resonance Imaging (MRI)
The most widely used form of brain imaging, MRI can provide information about both the structure and the function of the brain. Functional MRI (fMRI) is a technique that measures the activity of different brain regions as subjects lie inside the MRI scanner. It works by measuring changes in blood flow and blood oxygenation that follow changes in neuronal activity. By comparing the signals obtained as subjects perform different tasks within the scanner, researchers can generate maps that show which parts of the brain are involved in different cognitive processes.
In this method, electrodes are mounted on a flexible cap that is fitted to the surface of the scalp, allowing researchers to record electrical signals from the brain, which are conducted through the skull. Although EEG lacks the spatial resolution of fMRI, it provides much more detailed information about the timing of brain activity.
MEG involves measuring tiny magnetic fluctuations at the surface of the head that result from electrical activity within the brain. In our scanner, an array of 306 magnetic detectors (called SQUIDS) are mounted in a special helmet that fits over the head, providing a view of brain activity that combines very high time resolution with good spatial localization. Because the signals of interest are very small compared to the earth’s magnetic field and other background sources, MEG is performed inside a special magnetically shielded room.
Near-infrared spectroscopy (NIRS)
NIRS s a technology that uses the absorption of near-infrared light to reveal changes in blood flow related to neural activity. Unlike fMRI, which requires participants to remain motionless inside the scanner, NIRS involves placing a cap with light emitters and detectors on the participant’s head. In the case of infants, this means that they can sit on their caregiver’s lap, with some freedom of motion while they participate in studies.