Figure 2-5. Blood oxygen level-dependent (BOLD) functional MRI. The image shown is from a subject performing repetitive motor functions (tapping a button) with his right finger. Superimposed upon the grayscale structural MRI image are areas of altered BOLD signal, in color, associated with the task. The most prominent signal (yellow) is in the left lateral cerebral cortex, corresponding to the right hand area of the precentral and postcentral gyri. Other sites of lesser signal (red, orange) include the supplementary motor area, which is near the midline anteriorly. (Image courtesy of Dr. Michael D. Fox. From Fox MD, Snyder AZ, Zacks JM, Raichle ME: Coherent spontaneous activity accounts for trial-to-trial variability in human evoked brain responses. Nat Neurosci 9:23, 2006. Reproduced with permission.)
Figure 2-6. Axial 18FDG-PET of a normal brain. The PET data is colorized and overlaid on a CT image. Brain areas with higher metabolic activity such as cortex and deep gray nuclei appear bright, and areas with lower metabolic activity such as white matter appear purple.
Figure 2-7 A. “10-20” is a measurement system designed to reliably reproduce electrode positions on different patients, regardless of head size. Electrodes are placed at intervals of either 10 or 20 percent of the hemi-circumference of the head. (Courtesy of Dr. Jay S. Pathmanathan.) B. Each channel represents the amplified recording of voltage changes over time between two electrodes. Normal alpha (8 to 12 per second) activity is present posteriorly (bottom channel). The top channel contains a large blink artifact. Note the striking reduction of the alpha rhythm with eye opening (arrow). C. Photic driving. During stroboscopic stimulation of a normal subject, a visually evoked response is seen posteriorly after each flash of light (signaled on the bottom channel). (continued)
Figure 2-7 (Continued) D. Stroboscopic stimulation at 14 flashes per second (bottom channel) has produced a photoparoxysmal response in this epileptic patient, evidenced by the abnormal spike and slow-wave activity toward the end of the period of stimulation. E. Large, slow, irregular delta waves are seen in the right frontal region (channels 1 and 2). In this case a glioblastoma was found in the right cerebral hemisphere, but the EEG does not differ basically from that produced by a stroke, abscess, or contusion. F. An EEG showing focal spike-and-wave discharges over the right frontal region (channels 1 to 3). The box isolates a single spike–wave transient. (continued)
Figure 2-7 (Continued) G. Phase reversal is shown between electrode pairs, F7-T3 and T3-T5, implying that the site of the spike generator is under the T3 electrode. (Courtesy of Dr. Jay S. Pathmanathan.) H. Localization of a spike in a montage that utilizes the right ear (A2) as a reference electrode. The amplitude of the transient at T3 is greater than at other locations, implying that the source of the spike is closest to the T3 electrode. (Courtesy of Dr. Jay S. Pathmanathan.) I. Absence seizures, showing generalized 3-per-second spike-and-wave discharge. The abnormal activity ends abruptly and normal background activity appears. (continued)