Jeremy Young

Blood Oxygenation Level-Dependent Visualization of Synaptic Relay Stations of Sensory Pathways along the Neuroaxis in Response to Graded Sensory Stimulation of a Limb

Blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) was used to test at which levels of the neuroaxis signals are elicited when different modalities of sensory information from the limbs ascend to cortex cerebri. We applied graded electric stimuli to the rat hindlimbs and used echo-planar imaging to monitor activity changes in the lumbar spinal cord and medulla oblongata, where primary afferents of painful and nonpainful sensation synapse, respectively. BOLD signals were detected in ipsilateral lumbar spinal cord gray matter using sufficiently strong stimuli. Using stimuli well below the threshold needed for signals to be elicited in the spinal cord, we found BOLD responses in dorsal medulla oblongata. The distribution of these signals is compatible with the neuroanatomy of the respective synaptic relay stations of the corresponding sensory pathways. Hence, the sensory pathways conducting painful and nonpainful information were successfully distinguished. The fMRI signals in the spinal cord were markedly decreased by morphine, and these effects were counteracted by naloxone. We conclude that fMRI can be used as a reliable and valid method to monitor neuronal activity in the rat spinal cord and medulla oblongata in response to sensory stimuli. Previously, we also documented BOLD signals from thalamus and cortex. Thus, BOLD responses can be elicited at all principal synaptic relay stations along the neuroaxis from lumbar spinal cord to sensory cortex. Rat spinal cord fMRI should become a useful tool in experimental spinal cord injury and pain research.

Somatotopy and Attentional Modulation of the Human Parietal and Opercular Regions

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.

A database generator for human brain imaging

Sharing scientific data containing complex information requires new concepts and new technology. NEUROGENERATOR is a database generator for the neuroimaging community. A database generator is a database that generates new databases. The scientists submit raw PET and fMRI data to NEUROGENERATOR, which then processes the data in a uniform way to create databases of homogeneous data suitable for data sharing, met-analysis and modelling the human brain at the systems level. These databases are then distributed to the scientists.

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. Hum. Brain Mapping 19:183–196, 2003.

Simulating activations with cytoarchitecture.

Cytoarchitectonic delineation of areas in post-mortem human brains provides the precise location of these areas. It has been possible to study the size and location of areas between post-mortem brains with multi-subject cytoarchitectonic data. If the structure–function relationship is assumed to be a one-to-one mapping for the purposes of inter-subject variability, then functional areas in the cortex will also adhere to the structure, and therefore, the location and size of cytoarchitectonic areas in the brain. Thus, it is possible to use the cytoarchitectonic data as being representative of the size and location of functional activations. Under this assumption, we simulated activations in cytoarchitectonic areas from ten post-mortem brains in this study. We then treated these data as we would a normal PET experiment. The purpose of this study is to demonstrate a standard PET image analysis on a simulated ten-subject PET study using cytoarchitecture to localize the activations. By doing so, we simulate activations with real inter-subject variability with the size and location of each area. Significant activations were obtained for activations simulated in areas 3a and 3b. A voxel-wise conjunction between simulated data and experimental data was made to better determine the underlying areas activated by the experimental tasks. This study presents a novel technique for demonstrating the effect of standard image analysis on the location and size of simulated activations as determined by cytoarchitectonic data from multiple subjects. Furthermore, this technique has been applied to better determine the underlying areas activated in an experiment.

Two mechanisms of protracted reaction times mediated by dissociable cortical networks

When people divide attention between two sensory modalities and respond rapidly to stimuli in either modality, the reaction times (RTs) are longer than when they selectively attend and respond to one sensory modality. There is a further increase in RT when subjects use different fingers to respond to stimuli from different modalities as compared to when they use the same finger for both modalities. Here we use functional magnetic resonance imaging to show that division of attention bilaterally activates the caudal prefrontal areas near the precentral sulcus and areas in the intraparietal sulcus. All RT tasks, whether different fingers for different modalities or one finger for both modalities was used, activated identical motor areas 4a, 4p, supplementary and cingulate, the basal ganglia and the ventral anterior thalami. The increased blood oxygen level‐dependent signal from motor cortical areas was anatomically distinct from the prefrontal/parietal areas. These anatomically dissociable neural substrates of division of attention and motor control may be responsible for the different types of RT delays that we have found. In the brain, there were no differences in the BOLD signal irrespective of whether the effector was specified a priori or was specified only after the sensory signal was received.