Comparison of fMRI Digit Representations of the Dominant and Non-dominant Hand in the Human Primary Somatosensory Cortex

The tactile digit representations in the primary somatosensory cortex have so far been mapped for either the left or the right hand. This study localized all ten digit representations in right-handed subjects and compared them within and across the left and right hands to assess potential differences in the functional organization of the digit map between hands and in the structural organization between hemispheres. Functional magnetic resonance imaging of tactile stimulation of each fingertip in BA 3b confirmed the expected lateral-anterior-inferior to medial-posterior-superior succession from thumb to little-finger representation, located in the post-central gyrus opposite to the motor hand knob. While the more functionally related measures, such as the extent and strength of activation as well as the Euclidean distance between neighboring digit representations, showed significant differences between the digits, no side difference was detected: the layout of the functional digit-representation map did not consistently differ between the left, non-dominant, and the right, dominant hand. Comparing the absolute spatial coordinates also revealed a significant difference for the digits, but not between the left and right hand digits. Estimating the individual subject's digit coordinates of one hand by within-subject mirroring of the other-hand digit coordinates across hemispheres yielded a larger estimation error distance than using averaged across-subjects coordinates from within the same hemisphere. However, both methods should only be used with care for single-subject clinical evaluation, as an average estimation error of around 9 mm was observed, being slightly higher than the average distance between neighboring digits

Higher-order brain areas associated with real-time functional MRI neurofeedback training of the somato-motor cortex

AbstractNeurofeedback (NFB) allows subjects to learn self-regulation of neuronal brain activation based on information about the ongoing activation. The implementation of real-time functional magnetic resonance imaging (rt-fMRI) for NFB training now facilitates the investigation into underlying processes.Our study involved 16 control and 16 training right-handed subjects, the latter performing an extensive rt-fMRI NFB training using motor imagery. A previous analysis focused on the targeted primary somato-motor cortex (SMC). The present study extends the analysis to the supplementary motor area (SMA), the next higher brain area within the hierarchy of the motor system. We also examined transfer-related functional connectivity using a whole-volume psycho-physiological interaction (PPI) analysis to reveal brain areas associated with learning.The ROI analysis of the pre- and post-training fMRI data for motor imagery without NFB (transfer) resulted in a significant training-specific increase in the SMA. It could also be shown that the contralateral SMA exhibited a larger increase than the ipsilateral SMA in the training and the transfer runs, and that the right-hand training elicited a larger increase in the transfer runs than the left-hand training. The PPI analysis revealed a training-specific increase in transfer-related functional connectivity between the left SMA and frontal areas as well as the anterior midcingulate cortex (aMCC) for right- and left-hand trainings. Moreover, the transfer success was related with training-specific increase in functional connectivity between the left SMA and the target area SMC.Our study demonstrates that NFB training increases functional connectivity with non-targeted brain areas. These are associated with the training strategy (i.e., SMA) as well as with learning the NFB skill (i.e., aMCC and frontal areas). This detailed description of both the system to be trained and the areas involved in learning can provide valuable information for further optimization of NFB trainings

On the Physiology of Normal Swallowing as Revealed by Magnetic Resonance Imaging in Real Time

The aim of this study was to assess the physiology of normal swallowing using recent advances in real-time magnetic resonance imaging (MRI). Therefore ten young healthy subjects underwent real-time MRI and flexible endoscopic evaluations of swallowing (FEES) with thickened pineapple juice as oral contrast bolus. MRI movies were recorded in sagittal, coronal, and axial orientations during successive swallows at about 25 frames per second. Intermeasurement variation was analyzed and comparisons between real-time MRI and FEES were performed. Twelve distinct swallowing events could be quantified by real-time MRI (start time, end time, and duration). These included five valve functions: oro-velar opening, velo-pharyngeal closure, glottal closure, epiglottic retroflexion, and esophageal opening; three bolus transports: oro-velar transit, pharyngeal delay, pharyngeal transit; and four additional events: laryngeal ascent, laryngeal descent, vallecular, and piriform sinus filling and pharyngeal constriction. Repetitive measurements confirmed the general reliability of the MRI method with only two significant differences for the start times of the velo-pharyngeal closure (t(8) = -2.4, P <= 0.046) and laryngeal ascent (t(8) = -2.6, P <= 0.031). The duration of the velo-pharyngeal closure was significantly longer in real-time MRI compared to FEES (t(8) = -3.3, P <= 0.011). Real-time MRI emerges as a simple, robust, and reliable tool for obtaining comprehensive functional and anatomical information about the swallowing process

Somatosensory Evoked Potentials In Chronic Pain Patients

Die Arbeit vergleicht die kortikale Reizverarbeitung bei chronischen Rückenschmerzpatienten und gesunden Kontrollpersonen. Als Stimuli wurden kurze elektrische Reize am Rücken und am Finger verwendet. Die sieben individuell bestimmten Reizstärken lagen zwischen der Wahrnehmungs- und der Toleranzschwelle, zusätzlich wurde ein Konstantreiz appliziert. Erfaßt wurden die physikalischen Reizstärken, das somatosensorisch evozierte Potential (SEP) im EEG und die subjektive Intensitätseinschätzung für folgende Analysen: (1) Schwellenunterschiede, (2) Korrelation zwischen Reizstärke und Intensitätsempfinden, (3) Amplitudenänderungen der P80-, N150-, P260-, P300-Komponenten des SEPs, (4) Korrelation der Amplituden mit den Reizstärken bzw. Intensitätsbewertungen, (5) Habituation, (6) Konstantreiz. Ergebnisse: (1) Schmerzpatienten haben signifikant erniedrigte Schwellen. (2) Schmerzpatienten haben einen deutlichen Anstieg in der Intensitätsbewertung über die höheren Reizintensitäten. (3) Schmerzpatienten zeigen eine erniedrigte P80-Amplitude nach Fingerstimulation und eine generell erniedrigte N150 Amplitude; die Amplituden der P260 und P300 zeigen bei höheren Reizintensitäten die erwartete Amplitudenerhöhung, die bei Kontrollpersonen ausbleibt. (4) Die Amplituden der endogenen SEP-Komponenten korrelieren hoch mit den Intensitätsbewertungen. (5) Habituation ist bei den Amplituden der endogenen SEP-Komponenten, nicht jedoch bei der Intensitätsbewertung nachweisbar. (6) Die Gruppen bewerten die Intensität des Konstantreizes gleich, zeigen jedoch Amplitudenunterschiede bei der P80- und P300 Komponente. Die Ergebnisse verdeutlichen, daß die kortikale Reizverarbeitung bei chronischen Schmerzpatienten verändert ist, was sich sowohl in Amplitudenunterschieden der SEP-Komponenten als auch in den Intensitätseinschätzungen zeigt. Im Diskussionsteil wird dargelegt, wie sich diese Ergebnisse in Überlegungen zur Genese und Aufrechterhaltung chronischer Schmerzen integrieren lassen könnten.The study compares the cortical stimulus processing in chronic back-pain patients and healthy controls. Short electric stimuli were applied to the back and the finger. Eight stimulus intensities were used: seven individually determined stimulation intensities between the sensation- and the tolerance thresholds as well as a constant stimulus. Stimulation intensities, somatosensory evoked potentials (SEP) in the EEG and subjective intensity evaluations were measured. The following analysis were carried out: (1) differences in perception thresholds, (2) correlation between stimulus intensities and stimulus evaluations, (3) amplitude differences in the P80-, N150-, P260-, P300-components of the SEPs, (4) correlation between the amplitudes and the stimulus intensities or stimulus evaluations, (5) habituation, (6) effects of the constant stimulus. Results: (1) Pain patients exhibit significantly lower thresholds. (2) Patients show a increase in stimulus evaluation across higher stimulus intensities. (3) Patients have smaller P80 amplitudes in reaction to finger stimulation, generally smaller N150 amplitudes and an increase in P260 and P300 to higher stimulus intensities, which is not present in the control group. (4) The endogenous SEP-components correlate highly with the intensity evaluations in both groups. (5) The amplitudes of the SEP-components do habituate but not the intensity evaluations. (6) The constant stimulus evokes similar intensity evaluation in both groups, but there are differences in the amplitude of the P80 and the P300 components. These results demonstrate distinct variations in the cortical processing of somatosensory stimuli in chronic pain patients. Changes in the amplitudes of different SEP-components as well as in stimulus evaluation point to a modification in the perception in these patients. The discussion section illustrates how these results could be linked to present hypothesis concerning the development and the sustenance of chronic pain

Revisiting a historic human brain with magnetic resonance imaging – the first description of a divided central sulcus

In 1860 and 1862, the German physiologist Wagner published two studies, in which he compared the cortical surfaces of brain specimens. This provided the first account of a rare anatomical variation – bridges across the central sulci in both hemispheres connecting the forward and backward facing central convolutions in one of the brains. The serendipitous rediscovery of the preserved historic brain specimen in the collections at Göttingen University, being mistaken as the brain of the mathematician C.F. Gauss, allowed us to further investigate the morphology of the bridges Wagner had described with magnetic resonance imaging (MRI). On the historic lithograph, current photographs and MRI surface reconstructions of the brain, a connection across the central sulcus can only be seen in the left hemisphere. In the right hemisphere, contrary to the description of Wagner, a connecting structure is only present across the postcentral sulcus. MRI reveals that the left-hemispheric bridge extends into the depth of the sulcus, forming a transverse connection between the two opposing gyri. This rare anatomical variation, generally not associated with neurological symptoms, would nowadays be categorized as a divided central sulcus. The left-hemispheric connection seen across the postcentral sulcus, represents the very common case of a segmented postcentral sulcus. MRI further disclosed a connection across the right-hemispheric central sulcus, which terminates just below the surface of the brain and is therefore not depicted on the historical lithography. This explains the apparent inconsistency between the bilateral description of bridges across the central sulci and the unilateral appearance on the brain surface. The results are discussed based on the detailed knowledge of anatomists of the late 19th century, who already recognized the divided central sulcus as an extreme variation of a deep convolution within the central sulcus

Differential Activation in Somatosensory Cortex for Different Discrimination Tasks

Maps of the body surface in somatosensory cortex have been shown to be highly plastic, altering their configuration in response to changes in use of body parts. The current study investigated alterations in the functional organization of the human somatosensory cortex resulting from massed practice. Over a period of 4 weeks, subjects were given synchronous tactile stimulation of thumb (D1) and little finger (D5) for 1 hr/d. They had to identify the orientation of the stimuli. Neuroelectric source localization based on high-resolution EEG revealed that, when subjects received passive tactile stimulation of D1 or D5, the representations of the fingers in primary somatosensory cortex were closer together after training than before. There was also an apparently correlative tendency to anomalously mislocalize near-threshold tactile stimuli equally to the distant finger costimulated during training rather than preferentially to the finger nearest to the finger stimulated in a post-training test. However, when the stimulus discrimination had to be made, neuroelectric source imaging revealed that the digital representations of D1 and D5 were further apart after training than before. Thus, the same series of prolonged repetitive stimulations produced two different opposite effects on the spatial relationship of the cortical representations of the digits, suggesting that differential activation in the same region of somatosensory cortex is specific to different tasks