Biomedical subjects

Christian Grefkes

Publications and source records attributed to Christian Grefkes.

11 recordsLinked to original sources

PubMed2006

The somatotopic organization of cytoarchitectonic areas on the human parietal operculum.

The secondary somatosensory cortex (SII) of nonhuman primates is located on the parietal operculum. In the monkey, electrophysiological and connectivity tracing studies as well as histological investigations provide converging evidence for 3 distinct cortical areas (SII, PV, and VS) within this region, each of which contains a complete somatotopic map. Although the equivalency of the parietal operculum as the location of SII between humans and nonhuman primates is undisputed, the internal organization of the human SII region is still largely unknown. Based on their topography, we have previously argued that the cytoarchitectonic areas OP 1, OP 4, and OP 3 may constitute the human homologues of areas SII, PV, and VS, respectively. To test this hypothesis, we here examined (using functional magnetic resonance imaging) the somatotopic organization of the human parietal operculum by applying tactile stimulation to the skin at 4 different locations on either side of the body (face, hands, trunk, and legs). The locations of the resulting activation foci were then compared with the cytoarchitectonic maps of this region. Data analysis revealed 2 somatotopic body representations on the lateral operculum in areas OP 1 and OP 4. The functional border between these 2 body maps was defined by a mirror reversal in the somatotopic arrangement and coincided with the cytoarchitectonically defined border between these 2 areas. This somatotopic arrangement closely matches that described for SII and PV in nonhuman primates. The data also suggested a third somatotopic map located deeper inside the Sylvian fissure in area OP 3. Based on the observed topographic arrangement and their functional response characteristics, we conclude that cytoarchitectonic areas OP1, OP 4, and OP 3 on the human parietal operculum constitute the human homologues of primate areas SII, PV, and VS, respectively.

Adult↗

PubMed2005

Transmitter receptors reveal segregation of cortical areas in the human superior parietal cortex: relations to visual and somatosensory regions.

Regional distributions of ligand binding sites of 12 different neurotransmitter receptors (glutamatergic: AMPA, kainate, NMDA; GABAergic: GABA(A), GABA(B); cholinergic: muscarinic M2, nicotinic; adrenergic: alpha1, alpha2; serotonergic: 5-HT1A, 5-HT2; dopaminergic: D1) were studied in human postmortem brains by means of quantitative receptor autoradiography. Binding site densities were measured in the superior parietal lobule (SPL) (areas 5L, 5M, 5Ci, and different locations within Brodmann's area (BA) 7), somatosensory (BA 2), and visual cortical areas (BA 17, and different locations within BAs 18 and 19). Similarities of receptor distribution between cortical areas were analyzed by cluster analysis, uni- and multivariate statistics of mean receptor densities (averaged over all cortical layers), and profiles representing the laminar distribution patterns of receptors. A considerable heterogeneity of regional receptor densities and laminar patterns between the sites was found in the SPL and the visual cortex. The most prominent regional differences were found for M2 receptors. In the SPL, rostrocaudally oriented changes of receptor densities were more pronounced than those in mediolateral direction. The receptor distribution in the rostral SPL was more similar to that of the somatosensory cortex, whereas caudal SPL resembled the receptor patterns of the dorsolateral extrastriate visual areas. These results suggest a segregation of the different SPL areas based on receptor distribution features typical for somatosensory or visual areas, which fits to the dual functional role of this cortical region, i.e., the involvement of the human SPL in visuomotor and somatosensory motor transformations.

Aged↗

PubMed2005

A new SPM toolbox for combining probabilistic cytoarchitectonic maps and functional imaging data.

Correlating the activation foci identified in functional imaging studies of the human brain with structural (e.g., cytoarchitectonic) information on the activated areas is a major methodological challenge for neuroscience research. We here present a new approach to make use of three-dimensional probabilistic cytoarchitectonic maps, as obtained from the analysis of human post-mortem brains, for correlating microscopical, anatomical and functional imaging data of the cerebral cortex. We introduce a new, MATLAB based toolbox for the SPM2 software package which enables the integration of probabilistic cytoarchitectonic maps and results of functional imaging studies. The toolbox includes the functionality for the construction of summary maps combining probability of several cortical areas by finding the most probable assignment of each voxel to one of these areas. Its main feature is to provide several measures defining the degree of correspondence between architectonic areas and functional foci. The software, together with the presently available probability maps, is available as open source software to the neuroimaging community. This new toolbox provides an easy-to-use tool for the integrated analysis of functional and anatomical data in a common reference space.

Brain↗

PubMed2005

Subdivisions of human parietal area 5 revealed by quantitative receptor autoradiography: a parietal region between motor, somatosensory, and cingulate cortical areas.

Brodmann's area (BA) 5 of the human superior parietal cortex occupies a central anatomical position between the primary motor (BA 4), somatosensory (area 3b and BA 2), cingulate (area 23c), and superior parietal association cortex (BA 7). We studied the regional and laminar distributions of the binding sites of 12 different neurotransmitter receptors (glutamatergic: AMPA, kainate, NMDA; GABAergic: GABAA, GABAB; cholinergic: muscarinic M2, nicotinic; adrenergic: alpha1, alpha2; serotoninergic: 5-HT1A, 5-HT2; dopaminergic: D1) in human postmortem brains by means of quantitative receptor autoradiography, since the structural and functional aspects of human BA 5 are widely unknown, and previous observations have demonstrated characteristic differences in receptor distribution between motor and somatosensory areas. Binding site densities were measured in the cytoarchitectonically defined BA 5 and surrounding regions. Similarities and differences of receptor distribution between cortical areas were studied by cluster analysis of mean binding site densities averaged over all cortical layers, univariate and multivariate statistics, and by density profiles representing laminar receptor distribution patterns. Based on regional heterogeneities of binding site densities and of the cytoarchitecture within BA 5, we suggest a subdivision into three subareas: medial area 5M, lateral area 5L, and area 5Ci in the region around the cingulate sulcus. BA 5 is therefore a heterogeneous cortical region, comprising three subareas showing receptor expression patterns similar to the adjoining higher order somatosensory, multimodal parietal, or cingulate regions. These findings suggest that human BA 5 constitutes a higher order cortical area, clearly distinct from the primary somatosensory and motor cortex.

Aged↗

PubMed2005

The functional organization of the intraparietal sulcus in humans and monkeys.

In macaque monkeys, the posterior parietal cortex (PPC) is concerned with the integration of multimodal information for constructing a spatial representation of the external world (in relation to the macaque's body or parts thereof), and planning and executing object-centred movements. The areas within the intraparietal sulcus (IPS), in particular, serve as interfaces between the perceptive and motor systems for controlling arm and eye movements in space. We review here the latest evidence for the existence of the IPS areas AIP (anterior intraparietal area), VIP (ventral intraparietal area), MIP (medial intraparietal area), LIP (lateral intraparietal area) and CIP (caudal intraparietal area) in macaques, and discuss putative human equivalents as assessed with functional magnetic resonance imaging. The data suggest that anterior parts of the IPS comprising areas AIP and VIP are relatively well preserved across species. By contrast, posterior areas such as area LIP and CIP have been found more medially in humans, possibly reflecting differences in the evolution of the dorsal visual stream and the inferior parietal lobule. Despite interspecies differences in the precise functional anatomy of the IPS areas, the functional relevance of this sulcus for visuomotor tasks comprising target selections for arm and eye movements, object manipulation and visuospatial attention is similar in humans and macaques, as is also suggested by studies of neurological deficits (apraxia, neglect, Bálint's syndrome) resulting from lesions to this region.

Animals↗

PubMed2004

Dominance of the right hemisphere and role of area 2 in human kinesthesia.

We have previously shown that motor areas are engaged when subjects experience illusory limb movements elicited by tendon vibration. However, traditionally cytoarchitectonic area 2 is held responsible for kinesthesia. Here we use functional magnetic resonance imaging and cytoarchitectural mapping to examine whether area 2 is engaged in kinesthesia, whether it is engaged bilaterally because area 2 in non-human primates has strong callosal connections, which other areas are active members of the network for kinesthesia, and if there is a dominance for the right hemisphere in kinesthesia as has been suggested. Ten right-handed blindfolded healthy subjects participated. The tendon of the extensor carpi ulnaris muscles of the right or left hand was vibrated at 80 Hz, which elicited illusory palmar flexion in an immobile hand (illusion). As control we applied identical stimuli to the skin over the processus styloideus ulnae, which did not elicit any illusions (vibration). We found robust activations in cortical motor areas [areas 4a, 4p, 6; dorsal premotor cortex (PMD) and bilateral supplementary motor area (SMA)] and ipsilateral cerebellum during kinesthetic illusions (illusion-vibration). The illusions also activated contralateral area 2 and right area 2 was active in common irrespective of illusions of right or left hand. Right areas 44, 45, anterior part of intraparietal region (IP1) and caudo-lateral part of parietal opercular region (OP1), cortex rostral to PMD, anterior insula and superior temporal gyrus were also activated in common during illusions of right or left hand. These right-sided areas were significantly more activated than the corresponding areas in the left hemisphere. The present data, together with our previous results, suggest that human kinesthesia is associated with a network of active brain areas that consists of motor areas, cerebellum, and the right fronto-parietal areas including high-order somatosensory areas. Furthermore, our results provide evidence for a right hemisphere dominance for perception of limb movement.

Adult↗

PubMed2004

Human medial intraparietal cortex subserves visuomotor coordinate transformation.

In the macaque, the posterior parietal cortex (PPC) integrates multimodal sensory information for planning and coordinating complex movements. In particular, the areas around the intraparietal sulcus (IPS) serve as an interface between the sensory and motor systems to allow for coordinated movements in space. Because recent imaging studies suggest a comparable functional and anatomical organization of human and monkey IPS, we hypothesized that in humans, as in macaques, the medial intraparietal cortex (area MIP) subserves visuomotor transformations. To test this hypothesis, changes of neural activity were measured using functional magnetic resonance imaging (fMRI) while healthy subjects performed a joystick paradigm similar to the ones previously employed in macaques for studying area MIP. As hypothesized, visuomotor coordinate transformation subserving goal-directed hand movements activated superior parietal cortex with the local maximum of increased neural activity lying in the medial wall of IPS. Compared to the respective visuomotor control conditions, goal-directed hand movements under predominantly proprioceptive control activated a more anterior part of medial IPS, whereas posterior medial IPS was more responsive to visually guided hand movements. Contrasting the two coordinate transformation conditions, changing the modality of movement guidance (visual/proprioceptive) did not significantly alter the BOLD signal within IPS but demonstrated differential recruitment of modality specific areas such as V5/MT and sensorimotor cortex/area 5, respectively. The data suggest that the human medial intraparietal cortex subserves visuomotor transformation processes to control goal-directed hand movements independently from the modality-specific processing of visual or proprioceptive information.

Adult↗

PubMed2003

Regional cerebral blood flow correlations of somatosensory areas 3a, 3b, 1, and 2 in humans during rest: a PET and cytoarchitectural study.

The concept of functional connectivity relies on the assumption that cortical areas that are directly anatomically connected will show correlations in regional blood flow (rCBF) or regional metabolism. We studied correlations of rCBF of cytoarchitectural areas 3a, 3b, 1, and 2 in the brains of 37 subjects scanned with PET during a rest condition. The cytoarchitectural areas, delineated from 10 postmortem brains with statistical methods, were transformed into the same standard anatomical format as the resting PET images. In areas 3a, 3b, and 1, somatotopically corresponding regions were intercorrelated. Area 2 was correlated with the dorsal pre-motor area. These results were in accordance with the somatosensory connectivity in macaque monkeys. In contrast, we also found correlations between areas 3b and 1 with area 4a, and SMA, and among the left and right hand sector of areas 3a, 3b, and 1. Furthermore, there were no correlations between areas 3b, 1, and 2 with SII or other areas in the parietal operculum, nor of other areas known to be directly connected with areas 3a, 3b, 1, and 2 in macaques. This indicates that rCBF correlations between cortical areas during the rest state only partly reflect their connectivity and that this approach lacks sensitivity and is prone to reveal spurious or indirect connectivity.

Adult↗

PubMed2003

Somatosensory areas engaged during discrimination of steady pressure, spring strength, and kinesthesia.

The aim of this study was to locate neuronal populations in the somatosensory areas engaged during discrimination of differences in: (1) static sustained pressure on the distal phalanx (PRESS); (2) spring strengths (SSTIFF) during active flexion of the right index finger; and (3) the change in position of a limb with contracting muscles, i.e., kinesthesia (KIN), during active flexion of the right index finger. The stimuli used were spring-loaded cylinders. The regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET). The active fields were related to cytoarchitectonic areas of the somatosensory cortex (areas 3a, 3b, 1, and 2) and the primary motor cortex (areas 4a and 4p). We hypothesized that SSTIFF and KIN would activate areas 3a and 2. All three conditions, when contrasted against a rest condition, activated cytoarchitectural areas 3b, 1, and 2, and presumptive somatosensory areas in the left parietal operculum and right supramarginal gyrus in accordance with these areas receiving information from cutaneous mechanoreceptive afferents. Area 3a was only activated in SSTIFF and KIN, consistent with observations in monkeys and cats, showing that afferents from muscle receptors project to area 3a, and indicating that a similar arrangement seems to be apparent in humans. SSTIFF and KIN activated the right anterior lobe of the cerebellum, the left area 4a and left area 2 more than did PRESS, likely due to a combination of active movements and muscle receptor feed-back.

Adult↗

PubMed2003

Performing allocentric visuospatial judgments with induced distortion of the egocentric reference frame: an fMRI study with clinical implications.

The temporary improvement of visuospatial neglect during galvanic vestibular stimulation (Scand. J. Rehabil. Med. 31 (1999)117) may result from correction of the spatial reference frame distorted by the responsible lesion. Prior to an investigation of the neural basis of this effect in neurological patients, exploration of the neural mechanisms underlying such procedures in normals is required to provide insight into the physiological basis thereof. Despite their clinical impact, the neural mechanisms underlying the interaction of galvanic (and other) vestibular manipulations with visuospatial processing (and indeed the neural bases of how spatial reference frames are computed in man) remain to be clarified. We accordingly used fMRI in normal volunteers to investigate the effect of galvanically induced interference with the egocentric spatial reference frame on the neural processes underlying allocentric visuospatial (line bisection) judgments. A significant specific interaction of galvanic vestibular stimulation with the neural mechanisms underlying allocentric visuospatial judgments was observed in right posterior parietal and ventral premotor cortex only. Activation of these areas previously found to be damaged in visuospatial neglect suggests that these effects reflect the increased processing demands when compensating for the distorted egocentric spatial reference frame while maintaining accurate performance during the allocentric spatial task. These results thus implicate right posterior parietal and right ventral premotor cortex in the computation of spatial reference frames. Furthermore, our data imply a specific physiological basis for the temporary improvement of visuospatial neglect in patients with right hemisphere lesions during galvanic vestibular stimulation and may thus impact upon the rehabilitation of neglect: understanding the interaction of galvanic vestibular stimulation with allocentric visuospatial judgments in healthy volunteers may lead to the more effective deployment of such techniques in neurological patients.

Adult↗

PubMed2002

Crossmodal processing of object features in human anterior intraparietal cortex: an fMRI study implies equivalencies between humans and monkeys.

The organization of macaque posterior parietal cortex (PPC) reflects its functional specialization in integrating polymodal sensory information for object recognition and manipulation. Neuropsychological and recent human imaging studies imply equivalencies between human and macaque PPC, and in particular, the cortex buried in the intraparietal sulcus (IPS). Using functional MRI, we tested the hypothesis that an area in human anterior intraparietal cortex is activated when healthy subjects perform a crossmodal visuo-tactile delayed matching-to-sample task with objects. Tactile or visual object presentation (encoding and recognition) both significantly activated anterior intraparietal cortex. As hypothesized, neural activity in this area was further enhanced when subjects transferred object information between modalities (crossmodal matching). Based on both the observed functional properties and the anatomical location, we suggest that this area in anterior IPS is the human equivalent of macaque area AIP.

Adult↗