Eeg

EEG recordings provide functional brain information. EEG was first used to make functional brain images of cortical electrical signals in the 1970s when computers allowed the integration of simultaneous EEG recordings from multiple electrode sites and interpolation among sites. Early EEG images displayed EEG parameters (e.g., alpha, beta, theta waves) interpolated across the surface of the cortex using from 8 to 16 electrode sites. The placement of the electrodes was standard, using head landmarks, and each person's data was fit to a standard brain outline, pioneering many of the techniques subsequently applied to PET and MRI. The pattern of EEG activity over the cortical surface could be displayed from task to task, millisecond by millisecond and, as computers became more powerful, these displays even could be shown in real time. Evoked potentials (EP), a special EEG technique that averages EEG to specific stimuli over many trials, also can be displayed as an image using the same interpolation methods. One of a number of early methods to display such images was Brain Electric Activity Mapping (BEAM). Spatial resolution for EEG and

Figure 6 Structural MRI. Reconstructions are shown in one head injury patient with brain damage (dark areas) to the frontal lobe, especially in the right hemisphere. The upper left shows a 3-dimensional view, the upper right shows an axial view, the lower left shows a sagittal view and the lower right shows a coronal view. (Courtesy of Dr. Erin Bigler.)

Figure 6 Structural MRI. Reconstructions are shown in one head injury patient with brain damage (dark areas) to the frontal lobe, especially in the right hemisphere. The upper left shows a 3-dimensional view, the upper right shows an axial view, the lower left shows a sagittal view and the lower right shows a coronal view. (Courtesy of Dr. Erin Bigler.)

EP images depend on the number of electrode sites. The more sites, the more accurate the interpolations among sites. Arrays of more than 100 electrodes currently provide the best spatial resolution. Time resolution is millisecond by millisecond, essentially real time, and far exceeds all other functional imaging techniques. EEG and EP also are relatively inexpensive and logistically easy to use. There is no restriction for repeated testing in adults or children. The spatial resolution with more than 100 electrode sites is similar to PET but only the cortical surface is shown most accurately. There are advances in computing the possible deep brain sources for cortical signals. Gevins and colleagues have pushed EEG and EP methods to their limits for describing complex temporal topographic patterns of electrical activity during sensory, motor, and cognitive tasks (see Fig. 8).

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