Functional magnetic resonance imaging of sensory and motor cortex: comparison with electrophysiological localization

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✓ Functional magnetic resonance (MR) imaging was performed using a 1.5-tesla MR system to localize sensorimotor cortex. Six neurologically normal subjects were studied by means of axial gradient-echo images with a motor task and one or more sensory tasks: 1) electrical stimulation of the median nerve; 2) continuous brushing over the thenar region; and 3) pulsed flow of compressed air over the palm and digits. An increased MR signal was observed in or near the central sulcus, consistent with the location of primary sensory and motor cortex.

Four patients were studied using echo planar imaging sequences and motor and sensory tasks. Three patients had focal refractory seizures secondary to a lesion impinging on sensorimotor cortex. Activation seen on functional MR imaging was coextensive with the location of the sensorimotor area determined by evoked potentials and electrical stimulation. Functional MR imaging provides a useful noninvasive method of localization and functional assessment of sensorimotor cortex.

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Address reprint requests to: Aina Puce, Ph.D., Neuropsychology Laboratory/116B1, Veterans Affairs Medical Center, West Haven, Connecticut 06516.

© AANS, except where prohibited by US copyright law."

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    Functional magnetic resonance (MR) imaging data analysis procedure depicting generation of masked and thresholded t-maps. A: An unthresholded t-map (data from the motor task) showing significant areas of activation produced at each tail of the t-distribution for right versus left stimulation. Significant areas of activation are seen at extremes of the color scale (right side of figure), where left-sided activation appears as positive t-values and right-sided activation as negative t-values. The values around 0 appear in blue in the remainder of the image. B: Thresholded and masked t-map. Thresholds used: positive tail +3.0 to +10.0; negative tail: −8.0 to −3.0. An individual gradient-echo functional MR image was used to mask the t-map to include only pixels within the brain. C: Overlay of masked and thresholded t-map on anatomical T1-weighted image. A single color has been used for each tail of the t-distribution for optimum visibility (red = positive tail; green = negative tail). D: An unthresholded split t-map. Significant areas of activation produced at each tail of the t-distribution for right versus left motor-task comparison. Note that most t-values now are centered around 0 in the remainder of the image, as shown by the blue background in the image. E: Thresholded and masked split t-map. Thresholds used: positive tail +2.5 to +8.0; negative tail:−6.0 to −2.5. F: Overlay of masked and thresholded split t-map over T1-weighted anatomical image. Activation shown in red denotes the positive tail of the t-test, whereas green shows the negative tail.

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    Functional magnetic resonance (MR) images in two controls using the motor task. Significant areas of activation in masked and thresholded split t-maps are overlaid on corresponding anatomical images and indicated by colored areas. Thresholds for all t-maps shown were −3.5 for the negative tail (shown in green) and +4.0 for the positive tail (shown in red). A: Control 1. Inferior axial slice showing perirolandic activation. B: Superior axial slice showing activation contiguous with that seen in A. C: Repeat functional MR image showing similar activation to that seen previously in the inferior slice in A. D: Repeat functional MR image of superior slice B. E: Control 2. Inferior axial slice showing activation confined to the area of the central sulcus. F: Superior slice showing activation contiguous with inferior slice E. G: Repeat functional MR image showing inferior slice and activation similar to E. H: Repeat functional MR image showing superior slice and similar activation to F.

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    Thresholded split t-maps overlaid on a T1-weighted anatomical image in one control for the motor, brushing, and air tasks showing contiguous areas of activation in two axial slices (red = positive tail of t-test, green = negative tail). A: Motor task, inferior slice.B: Motor task, slice superior to A. C: Brushing task, inferior slice. D: Brushing task, slice superior to C. E: Air task, inferior slice, corresponding to the superior slice in B and D. (Slice superior to E not shown.)

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    Functional magnetic resonance imaging activation produced by electrical stimulation of the median nerve at three frequencies shown in thresholded masked split t-maps (negative tail less than −1.5, positive tail greater than +1.5) overlaid on a T1-weighted anatomical image. A: 5-Hz condition. No activation is seen. B: 15-Hz condition. Activation is seen in the left perirolandic region in response to right median nerve stimulation (shown in green and identified by arrow). C: 30-Hz condition. Activation is seen in the left postcentral cortex only (shown in green and identified with arrow).

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    Comparison of functional localization by functional magnetic resonance (MR) imaging and electrophysiological methods in Case 1. a: Schematic drawing showing electrode locations for intraoperative somatosensory evoked potential (SSEP) recording. Closed circles indicate recording sites of SSEPs shown in b. Broken circles indicate extrapolated electrode locations. Cortical stimulation produces thumb movement at A, finger flexion at B, and forearm pronation at C; D indicates a stereotactic biopsy of the lesion. b: Graph of SSEP recordings showing polarity reversal of the 20- and 30-msec potentials across the central sulcus (CS) from electrode locations 36 to 37. c: Photograph of superior view of the rendered surface of the brain showing the lesion (yellow), the hand sensory cortex as identified by SSEPs (white), the hand motor cortex as identified by cortical stimulation (blue), and the hand sensory (green) and motor (red) areas as identified by functional MR imaging. PoCS = postcentral sulcus; Cr = craniotomy margin.

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    Comparison of functional localization by functional magnetic resonance (MR) imaging and electrophysiological methods in Case 2. a: Schematic drawing showing electrode locations for intraoperative somatosensory evoked potential (SSEP) recording. Closed circles indicate recording sites of SSEPs shown in b. The hand motor area identified from cortical stimulation is shown by A and the lesion is indicated by diagonal stripes. b: Graph of recordings showing polarity reversal of the 20- and 30-msec potentials across the central sulcus (CS) from electrode locations 19 to 21. c: Intraoperative photograph of electrode grid position and hand motor area, A, as seen from cortical stimulation. d: Superior view of the rendered surface of the brain showing the lesion (yellow), the hand sensory cortex as identified by SSEPs (white), the hand motor cortex identified by cortical stimulation (blue, white arrow) and by functional MR imaging (red). PoCS = postcentral sulcus; Cr = craniotomy margin; PrCS = precentral sulcus; SS = sylvian sulcus.

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    Photographs of rendered surface of the brain comparing functional localization by functional magnetic resonance (MR) imaging and electrophysiological methods in two patients. A: Case 3. Superior view showing the lesion (yellow), the hand sensory cortex identified by somatosensory evoked potentials (SSEPs) (white), the hand motor cortex identified by cortical stimulation (blue), and the hand sensory (green) and motor (red) areas identified by functional MR imaging. B: Case 4. Lateral view showing the hand sensory cortex identified by SSEPs (white), the hand motor cortex identified by cortical stimulation (blue) and functional MR imaging (red). Case 4 did not have sensory functional MR studies.

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