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The somatotopical organization of the postcentral gyrus is well known, but less is known about the somatotopical organization of area 2, the somatosensory association areas in the postparietal cortex, and the parietal operculum. The extent to which these areas are modulated by attention is also poorly understood. For these reasons, we measured the BOLD signal when rectangular parallelepipeds of varying shape were presented to the immobile right hand or right foot of 10 subjects either discriminating these or just being stimulated. Activation areas in each subject were mapped against cytoarchitectural probability maps of area 2, IP1, and IP2 along the intraparietal sulcus and the parietal opercular areas OP1-OP4. In area 2, the somatotopical representation of the hand and foot were distinctly separate, whereas there was considerable overlap in IP1 and no clear evidence of separate representations in OP1, OP4, and IP2. The overlap of hand and foot representations increased in the following order: area 3a, 3b, 1, 2, IP1, OP4, IP2, and OP1. There were significant foot representations but no hand representations in right (ipsilateral) areas 3a, 3b, and 1. Shape discrimination using the foot as opposed to stimulation enhanced the signal in OP4 bilaterally, whereas discrimination with the hand enhanced the signal bilaterally in area 2, IP1, and IP2. These results indicate that somatosensory areas in humans are arranged from strong somatotopy into no somatotopy in the following order: 3a, 3b, 1, 2, IP1, OP4, IP2, and OP1. Higher order areas such as IP1, IP2, and OP4 showed task-related attentional enhancement. [ABSTRACT FROM AUTHOR]

In this study we analyzed structural and functional aspects of the human primary somatosensory areas 3a, 3b, and 1 on the basis of a computerized brain atlas. The approach overcomes many of the problems associated with subjective architectonic parcellations of the cortex and with ”classical” brain maps published in a ”rigid” print format. Magnetic resonance (MR) scans were obtained from ten postmortem brains. The brains were serially sectioned at 20 µm, and sections were stained for cell bodies. Areas 3a, 3b, and 1 were delineated statistically on the basis of differences in the laminar densities of neuronal cell bodies. The borders of the areas were topographically variable across different brains and did not match macroanatomical landmarks of the postcentral gyrus. After correction of the sections for deformations due to histological processing, each brain’s 3-D reconstructed histological volume and the volume representations of areas 3a, 3b, and 1 were adapted to the reference brain of a computerized atlas and superimposed in 3-D space. For each area, a population map was generated that described, for each voxel, how many brains had a representation of that area. Despite considerable interindividual variability, representations of areas 3a, 3b, and 1 in ≥50% of the brains were found in the fundus of the central sulcus, in the rostral bank, and on the crown of the postcentral gyrus, respectively. For each area, a volume of interest (VOI) was defined that encompassed that area’s representation in ≥50% of the brains. Despite close spatial relationship in the postcentral gyrus, the three VOIs overlapped by <1% of their volumes. Changes in regional cerebral blood flow (rCBF) were measured with positron emission tomography when six right-handed subjects discriminated differences in the speed of a rotating brush stimulating the palmar surface of the right hand. With co-registered MR images, the rCBF data were adapted to the same reference brain and superimposed with the microstructural VOIs. Discrimination of moving stimuli, contrasted to rest, increased the rCBF in the VOIs of areas 3b and 1, but not in area 3a. This approach opens up the possibility of (1) defining VOIs of cortical areas which are not based on macroanatomical landmarks but instead on observer-independent cytoarchitectonic mapping of postmortem brains and of (2) determining in these VOIs changes in rCBF data obtained from functional imaging experiments. [ABSTRACT FROM AUTHOR]

Fluoromethane, previously labelled with F and used as a tracer in the measurement of regional cerebral blood flow, was C-labelled by the reaction of C-methyl iodide with tetraethylammonium fluoride. Sufficient quantities of radiotracer were prepared with a minimum amount of handling from 15 min target irradiations in the N( p, α) C reaction. Total synthesis time was 25 min from end-of-bombardment, allowing serial blood flow measurements 30 min apart. The use of C-fluoromethane as a cerebral blood flow tracer in positron emission tomography is discussed. [ABSTRACT FROM AUTHOR]

Presents information on the findings of a study which suggests that roughness discrimination compared with a motor control activates the parietal operculum (LPO), and that this is significantly more activated by roughness than by length discrimination. Material and methods used; How the motor components of the roughness discrimination and shape discrimination differs; Results and discussion of the study.

How do neurons and networks of neurons interact spatially? Here, we overview recent discoveries revealing how spatial dynamics of spiking and postsynaptic activity efficiently expose and explain fundamental brain and brainstem mechanisms behind detection, perception, learning, and behavior. How do neurons and networks of neurons interact spatially? Here, Grün et al. overview recent discoveries revealing how spatial dynamics of spiking and postsynaptic activity efficiently expose and explain fundamental brain and brainstem mechanisms behind detection, perception, learning, and behavior. [ABSTRACT FROM AUTHOR]