Segregation of somatosensory activation in the human rolandic cortex usingfMRI

The segregation of sensory information into distinct cortical areas is an i mportant organizational feature of mammalian sensory systems. Here, we prov ide functional magnetic resonance imaging (fMRI) evidence for the functiona l delineation of somatosensory representations in the human central sulcus region. Data were collected with a 3-Tesla scanner during two stimulation p rotocols, a punctate tactile condition without a kinesthetic/motor componen t, and a kinesthetic/motor condition without a punctate tactile component. With three-dimensional (3-D) anatomical reconstruction techniques, we analy zed data in individual subjects, using the pattern of activation and the an atomical position of specific cortical areas to guide the analysis. As a co mplimentary analysis, we used a brain averaging technique that emphasized t he similarity of cortical features in the morphing of individual subjects a nd thereby minimized the distortion of the location of cortical activation sites across individuals. A primary finding of this study was differential activation of the cortex on the fundus of the central sulcus, the position of area 3a, during the two tasks. Punctate tactile stimulation of the palm, administered at 3 Hz with a 5.88(log10.mg) von Frey filament, activated di screte regions within the precentral (PreCG) and postcentral (PoCG) gyri, c orresponding to areas 6, 3b, 1, and 2, but did not activate area 3a. Conver sely, kinesthetic/motor stimulation, 3-Hz flexion and extension of the digi ts, activated area 3a, the PreCG (areas 6 and 4), and the PoCG (areas 3b, 1 , and 2). These activation patterns were observed in individual subjects an d in the averaged data, providing strong evidence for the existence of a di stinct representation within area 3a in humans. The percentage signal chang es in the PreCG and PoCG regions activated by tactile stimulation, and in t he intervening gap region, support this functional dissociation. In additio n to this distinction within the fundus of the central sulcus, the combinat ion of high-resolution imaging and 3-D analysis techniques permitted locali zation of activation within areas 6, 4, 3a, 3b, 1, and 2 in the human. With the exception of area 4, which showed inconsistent activation during punct ate tactile stimulation, activation in these areas in the human consistentl y paralleled the pattern of activity observed in previous studies of monkey cortex.