Integration of target and effector information in human posterior parietal cortex for the planning of action

Recently, using event-related functional MRI (fMRI), we located a bilateral region in the human posterior parietal cortex (retIPS) that topographically represents and updates targets for saccades and pointing movements in eye-centered coordinates. To generate movements, this spatial information must be integrated with the selected effector. We now tested whether the activation in retIPS is dependent on the hand selected. Using 4-T fMRI, we compared the activation produced by movements, using either eyes or the left or right hand, to targets presented either leftward or rightward of central fixation. The majority of the regions activated during saccades were also activated during pointing movements, including occipital, posterior parietal, and premotor cortex. The topographic retIPS region was activated more strongly for saccades than for pointing. The activation associated with pointing was significantly greater when pointing with the unseen hand to targets ipsilateral to the hand. For example, although there was activation in the left retIPS when pointing to targets on the right with the left hand, the activation was significantly greater when using the right hand. The mirror symmetric effect was observed in the right retIPS. Similar hand preferences were observed in a nearby anterior occipital region. This effector specificity is consistent with previous clinical and behavioral studies showing that each hand is more effective in directing movements to targets in ipsilateral visual space. We conclude that not only do these regions code target location, but they also appear to integrate target selection with effector selection.     

Computed tomography scanning with simultaneous patient translation

This paper deals with methods of reducing the total time required to acquire the projection data for a set of contiguous computed tomography (CT) images. Normally during the acquisition of a set of slices, the patient is held stationary during data collection and translated to the next axial location during an interscan delay. We demonstrate using computer simulations and scans of volunteers on a modified scanner how acceptable image quality is achieved if the patient translation time is overlapped with data acquisition. If the concurrent patient translation is ignored, structured artifacts significantly degrade resulting reconstructions. We present a number of weighting schemes for use with the conventional convolution/backprojection algorithm to reduce the structured artifacts through the use of projection modulation using the data from individual and multiple slices. We compare the methods with respect to structured artifacts, noise, resolution and to patient motion. Review of preliminary results by a panel of radiologists indicates that the residual image degradation is tolerable for selected applications when it is critical to acquire more slices in a patient breathing cycle than is possible with conventional scanning.     

Immunocytochemical localization of a granuliberin-like peptide in Rana pipiens brain

The histamine-releasing peptide “granuliberin”, originally isolated from the skin of Rana rugosa, was localized by immunofluorescence within nerve cell bodies and fibers in the brain of Rana pipiens. The granuliberin-positive neurons were characterized ultrastructurally by electron microscopic observation of ultrathin sections stained either with immunoperoxidase or with conventional stains. Granuliberin-positive nerve cell bodies were seen throughout the hypothalamus, from the suprachiasmatic area rostrally to the full length of the periinfundibular grey matter caudally. Similarly positive nerve fibers were localized in the hypothalamus radiating upwards to the optic vesicles in the midbrain, extending through the preoptic area into the subpallium in the forebrain, and throughout the white matter surrounding the floor and lateral walls of the fourth ventricle in the brainstem. The granuliberin-positive nerve cells showed the presence of variable numbers of small cytoplasmic neurosecretory granules. Possessing an electron dense elongated core, and measuring 250–350 nm in their largest diameter. The functional significance of a granuliberin-like peptide in neurons of the frog brain is not known.     

Zinc deficiency conditions food aversions in rats

Zinc (Zn) deficiency is shown to condition aversion to the Zn-deficient diet. After development of a Zn deficiency syndrome during which consumption of the deficient diet decreased, rats readily consumed a familiar Zn-normal diet. After Zn repletion, the previously deficient animals continued to avoid the Zn-deficient diet. These results would not be predicted by the competing hypothesis that Zn-deficiency is anorexigenic.     

Definition of linear antigenic regions of the HPV16 L1 capsid protein using synthetic virion-like particles.

Mice of three haplotypes (H-2d, H-2b, and H-2d/b) were immunized with synthetic HPV16 virus-like particles (VLPs), produced using a vaccinia virus doubly recombinant for the L1 and L2 proteins of HPV16. The resultant anti-VLP antisera recognized HPV16 capsids by ELISA assay and baculovirus recombinant HPV16 L1 and L2 protein on immunoblot. Overlapping peptides corresponding to the HPV16 L1 amino acid sequence were used to define the immunoreactive regions of the L1 protein. The majority of the L1 peptides were reactive with IgG from the mice immunized with the synthetic HPV16 capsids. A computer algorithm predicted seven B epitopes in HPV16 L1, five of which lay within peptides strongly reactive with the murine antisera. The murine anti-VLP antisera failed to react with the two peptides recognized by anti-HPV16L1 monoclonal antibodies raised by others against recombinant L1 fusion protein. We conclude that the immunoreactive epitopes of HPV16 defined using virus-like particles differ significantly from those defined using recombinant HPV16 L1 fusion proteins, which implies that such fusion proteins may not be the antigens to look for HPV16L1 specific immune responses in HPV-infected patients.     

Fragile X CGG repeat structures among African-Americans: identification of a novel factor responsible for repeat instability

The cryptic CGG repeat responsible for the fragile X syndrome, located in the 5'-UTR of FMR1, is unique compared with the many other triplet repeat-causing diseases, making it ideal for identifying factors involved in repeat expansion that may be common to other triplet repeat diseases. To date, a number of factors have been identified which may influence repeat instability, including the number and position of interspersed AGGs, length of the 3' pure CGG repeat and haplotype background. However, nearly all such data were derived from studies of Caucasians. Using a large African-American population, we present the only comprehensive examination of factors associated with CGG repeat instability in a non-Caucasian population. Among Caucasians, susceptible alleles were thought to come from those in the intermediate repeat range (41-60 repeats); however, we find that susceptible alleles may come from a larger repeat pool (35-60 repeats) and are better defined by their pure CGG repeat and/or -presence of only one AGG interruption. These results demonstrate the existence of different susceptible alleles among world populations and may account for the similar prevalence of the fragile X syndrome in African-Americans compared with Caucasians despite the lower frequency of inter-mediate sized alleles in the African-American population. Finally, we show that repeat structures among unaffected African-Americans with the most frequent fragile X haplotype background are either pure or contain a single distal interruption. We propose that the lack of a proximal most interruption is a novel factor involved in CGG repeat instability.     

Contribution of head movement to gaze command coding in monkey frontal cortex and superior colliculus

Most of what we know about the neural control of gaze comes from experiments in head-fixed animals, but several "head-free" studies have suggested that fixing the head dramatically alters the apparent gaze command. We directly investigated this issue by quantitatively comparing head-fixed and head-free gaze trajectories evoked by electrically stimulating 52 sites in the superior colliculus (SC) of two monkeys and 23 sites in the supplementary eye fields (SEF) of two other monkeys. We found that head movements made a significant contribution to gaze shifts evoked from both neural structures. In the majority of the stimulated sites, average gaze amplitude was significantly larger and individual gaze trajectories were significantly less convergent in space with the head free to move. Our results are consistent with the hypothesis that head-fixed stimulation only reveals the oculomotor component of the gaze shift, not the true, planned goal of the movement. One implication of this finding is that when comparing stimulation data against popular gaze control models, freeing the head shifts the apparent coding of gaze away from a "spatial code" toward a simpler visual model in the SC and toward an eye-centered or fixed-vector model representation in the SEF.