Denis Le Bihan, MD, PhD; Peter Jezzard, PhD; James Haxby, PhD; Norihiro Sadato, MD, PhD; Linda Rueckert, PhD; Venkata Mattay, MD
This conference reviewed the potential scope of application for recently developed techniques for functional magnetic resonance imaging (fMRI) of the brain.The most successful technique is based on the sensitivity of magnetic resonance imaging (MRI) to magnetic effects caused by the modulation of the oxygenation state of hemoglobin, which is induced by local variations in blood flow during task activation. Typically, the MRI signal increases by a few percentage points during brain activation because blood flow and oxygen supply sharply increase. Brain activation images with excellent combined spatial and temporal resolution have been obtained noninvasively using visual, sensorimotor, or auditory stimuli, or during higher-order cognitive processes such as language or mental imagery. Although sensitive to misregistration artifacts and macroscopic vessels, MRI permits both the direct correlation of function with underlying anatomy and repeated studies on the same person. It may become the method of choice for studies of mental and cognitive processes, presurgical mapping, monitoring recovery from stroke or head injuries, exploration of seizure disorders, or monitoring the effects of neuropharmaceuticals.
Schematic time course from an idealized region of tissue in response to alternating periods of stimulus and rest. Time course from an experiment (visual cortex) in which a visual stimulus was presented to the participant. Note the delay and smear of the data relative to the input condition; this is caused by the slow (on the neuronal timescale) hemodynamic response.
Direct comparison of areas activated by selective attention to face identity and a sensorimotor control task in a positron emission tomography (PET) (regional cerebral blood flow) study of nine participants (left; adapted from reference 23) and a functional MRI study of a single participant ( ). The areas shown in color showed a significant difference between the face-matching and control tasks ( = 0.001 for both). The PET results are shown on coronal sections taken from the Talairach and Tournoux stereotactic brain atlas, 85 mm and 60 mm posterior to the anterior commissure. The functional MRI results are shown on coronal sections of a high-resolution MRI scan of the same participant. Data were obtained from echoplanar imaging volume sets of eight coronal sections, each 6 mm thick, collected every 6 seconds in the right posterior extrastriate cortex.
The activated area of the left primary motor cortex by self-paced sequential opponent finger movement of the right hand (approximately 2 Hz). The activated area in orange showed a z-score greater than 2. Time intensity curve of the left primary motor cortex, which followed the periodicity of the activation task (rest, ideation, rest, movement, rest, ideation, and rest). Activation by actual movement was more prominent (percentage increase of signal intensity compared with rest condition was 4.14 ±1.37 [mean ±SE]; = 0.000001, rank analysis of variance) than that by ideation (1.70 ±1.08; = 0.000005, rank analysis of variance), which was still significant.
42.5 mm left of midline. 42.5 mm right of midline. Orange areas are those for which mean signal intensity during the word-generation periods was at least 1 standard deviation higher than the mean during the control condition. Green areas are those for which word-generation intensity was at least 1 standard deviation below that for the control condition. The isolated region to the left is the eye and shows decreased signal because of eye movements. Data were obtained using a 4-tesla magnetic resonance imaging scanner with echoplanar imaging. The image resolution is 2.5 mm. Four contiguous 5-mm slices were acquired every 3 seconds.
Activation is seen in the left dorsolateral prefrontal cortex region in the normal volunteer. Lack of similar activation shows hypofrontality in the schizophrenic patient.
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Le Bihan D, Jezzard P, Haxby J, Sadato N, Rueckert L, Mattay V. Functional Magnetic Resonance Imaging of the Brain. Ann Intern Med. ;122:296–303. doi: 10.7326/0003-4819-122-4-199502150-00010
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Published: Ann Intern Med. 1995;122(4):296-303.
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