OCALIZATION of lateral cortical areas activated by cutaneous stimulation is important for both clinical localization of the central sulcus and understanding the complexities of sensory processing. Most of the cur- rent clinical literature regarding motor or somatosensory cortical localization focuses only on several areas. These include the primary motor area (Brodmann Area 4) or the primary sensory area ([SI]: Brodmann Areas 3a, 3b, 1, and 2) located in the postcentral gyrus. 1,8,20,27,31,34,37,42,54,55,65,72, 73,76,89 Few investigators publishing functional magnetic resonance (fMR) studies have extended these observa- tions to examine sensory areas other than SI even though clear experimental evidence exists that other cortical areas are activated by simple cutaneous stimuli in humans and other primates. 3,14,15,17,18,21,22,25,32,47–50,58,67,78,80,84 Other lateral cortical areas important for somatosensory information flow include the second somatosensory area (SII), which is located in the superior bank of the sylvian fissure; the parietal association areas, which are located in the superi- or and inferior parietal lobules; and the insula (INS). 13–15,18, 21,32,47,49,50,58,63,67,68,78,80,83 This study was undertaken to deter- mine if fMR imaging could be used to identify activation of the SI and other sensory areas in normal human volun- teers. The correlations between the amounts of activation in the identified sensory areas were also evaluated to un- derstand the functional relations better among these areas. These experiments were accomplished by mapping the T 2 * signal by using fMR imaging. This technique identi- fies focal neural activity based on activity-dependent changes in local blood oxygenation, blood flow, and blood volume 5,23,51,61 and is called the blood oxygenation level– dependent (BOLD) technique. Data collection was modi- fied using echoplanar imaging. This important modifica- tion of the BOLD technique allows rapid collection of data so that multiple samples of brain slices are obtained during control and activated states. 6,19,51,77 The ability to collect multiple images at each location allows statistical evaluation of the BOLD signal and, therefore, identifica- tion of areas of cortical activity elicited by the activa- tion task. Our results obtained using fMR imaging indicate that somatosensory stimuli result in robust activation of the SI, SII, INS, and parietal association areas. The large amount of activation noted in the retroinsular parietal operculum (RIPO) of the inferior parietal lobule is of particular in- terest. J. Neurosurg. / Volume 89 / November, 1998 J Neurosurg 89:769–779, 1998 Patterns of lateral sensory cortical activation determined using functional magnetic resonance imaging CHARLES J. HODGE, JR., M.D., SEAN C. HUCKINS, M.S., NIKOLAUS M. SZEVERENYI, PH.D., MICHAEL M. FONTE, M.D., JACOB G. DUBROFF , B.S., AND KRISHNA DAVULURI, B.S. Departments of Neurosurgery and Radiology, State University of New York Health Science Center at Syracuse, Syracuse, New York Object. Functional magnetic resonance (fMR) imaging was performed in human volunteers to determine the lat- eral perisylvian cortical areas activated by innocuous cutaneous stimulation. Methods. Eight volunteers who underwent 53 separate experiments form the basis of this report. Eight contigu- ous coronal slices were obtained using echoplanar fMR imaging techniques while participants were at rest and while somatosensory activation stimuli consisting of vibration or air puffs were delivered to various body areas. The data were analyzed using Student’s t-test and cluster analysis to determine significant differences between the resting and activated states. The findings were as follows: the areas in the lateral cortex activated by the sitmuli were the primary sensory cortex (SI), the second somatosensory area (SII), the insula, the superior parietal lobule, and the retroinsular parietal operculum (RIPO). Somatotopy was demonstrable in SI but not in the other areas identified. There was a surprisingly low correlation between the amount of cortex activated in the various areas, which could mean separate inputs and functions for the areas identified. The highest correlation was found between activity in SII and RIPO (0.69). Conclusions. The authors maintain that fMR imaging can be used to identify multiple lateral somatosensory areas in humans. Somatotopy is demonstrated in SI but not in the other lateral cortical sensory areas. The correlations between the amounts of cortex activated in the different lateral sensory areas are low. Recognition of the multiple lateral sensory areas is important both for understanding sensory cortical function and for safe interpretation of stud- ies designed to identify the central sulcus by activating SI. KEY WORDS • functional magnetic resonance imaging • sensory cortex • human anatomy • somatosensory mapping L 769