1,721,254 research outputs found
Tonotopic organization of the human auditory cortex revealed by steady state neuromagnetic measurements
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Sensitivity of BOLD response to increasing visual contrast: spin echo versus gradient echo EPI
No full textPrevious evidence showed that spin-echo (SE) BOLD signals offer an increased linearity and promptness with respect to gradient-echo (GE) acquisition, possibly providing a more accurate estimate of the amplitude of neuronal activity. However there is no evidence that the two sequences differ in representing different activation levels due to changes in stimulus intensity. In this study at 3T we compared GE and SE BOLD responses to visual stimuli at increasing contrast levels (5%, 20%, 60%, 100%). Both sequences showed a monotonic increase of the BOLD response with stimulus contrast. While the larger sensitivity of GE yielded overall larger signal changes, step-wise increase in activation for GE was significant only when comparing 20% with 5% contrast, whereas for SE a significant increase was observed also when comparing 60% with 20% contrast. Moreover, BOLD responses normalized to the lowest contrast showed that relative increases of SE fMRI signal with increasing stimulus strength are larger with respect to the corresponding values of GE signal. This difference was observed also when excluding voxels attributed to large vessels, suggesting a non negligible role of the extravascular contribution to the modulation of SE fMRI signal with stimulus intensity. These results are shown to be in agreement with theoretical predictions that we derived from a recently proposed model of GE and SE functional signals. The present findings suggest that, despite the limited increase in functional localization accuracy at low field, SE fMRI might offer a potential advantage in distinguishing different levels of stimulus-evoked brain activity
Reach Out and Touch Someone: Anticipatory Sensorimotor Processes of Active Interpersonal Touch
Full text linkAnticipating the sensorimotor consequences of an action for both self and other is fundamental for action coordination when individuals socially interact. Somatosensation constitutes an elementary component of social cognition and sensorimotor prediction, but its functions in active social behavior remain unclear. We hypothesized that the somatosensory system contributes to social haptic behavior as evidenced by specific anticipatory activation patterns when touching an animate target (human hand) compared with an inanimate target (fake hand). fMRI scanning was performed during a paradigm that allowed us to isolate the anticipatory representations of active interpersonal touch while controlling for nonsocial sensorimotor processes and possible confounds because of interpersonal relationships or socioemotional valence. Active interpersonal touch was studied both as skin-to-skin contact and as object-mediatedtouch. The results showed weaker deactivation in primary somatosensory cortex and medial pFC and stronger activation in cerebellum for the animate target, compared with the inanimate target, when intending to touch it with one's own hand. Differently, in anticipation of touching the human hand with an object, anterior inferior parietal lobule and lateral occipital-temporal cortex showed stronger activity. When actually touching a human hand with one's own hand, activation was stronger in medial pFC but weaker in primary somatosensory cortex. The findings provide new insight on the contribution of simulation and sensory prediction mechanisms to active social behavior. They also suggest that literally getting in touch with someone and touching someone by using an object might be approached by an agent as functionally distinct conditions
Functional localization of the sensory hand area with respect to the motor central gyrus knob
No full textThe aim of this work was to investigate the topography of the primary sensory hand cortex with magnetoencephalography in order to define the functional anatomy of this area in healthy humans. Previous studies denoted an inverted Ohm or an horizontal epsilon shaped knob on the pre-central gyrus as a landmark for the motor hand area; therefore a systematic difference between the orientation of the source for thumb with respect to little finger should be observed. We found this systematic difference, but the direction of the sources activated during thumb and little finger stimulation did not converge, as would be expected if only the Ohm convexity is activated: in fact our results suggest that thumb sensory area also extends to the area lateral to this convexity
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