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PubMedDate not supplied

In vivo three-dimensional surface geometry of abdominal aortic aneurysms.

Abdominal aortic aneurysm (AAA) is a local, progressive dilation of the distal aorta that risks rupture until treated. Using the law of Laplace, in vivo assessment of AAA surface geometry could identify regions of high wall tensions as well as provide critical dimensional and shape data for customized endoluminal stent grafts. In this study, six patients with AAA underwent spiral computed tomography imaging and the inner wall of each AAA was identified, digitized, and reconstructed. A biquadric surface patch technique was used to compute the local principal curvatures, which required no assumptions regarding axisymmetry or other shape characteristics of the AAA surface. The spatial distribution of AAA principal curvatures demonstrated substantial axial asymmetry, and included adjacent elliptical and hyperbolic regions. To determine how much the curvature spatial distributions were dependent on tortuosity versus bulging, the effects of AAA tortuosity were removed from the three-dimensional (3D) reconstructions by aligning the centroids of each digitized contour to the z axis. The spatial distribution of principal curvatures of the modified 3D reconstructions were found to be largely axisymmetric, suggesting that much of the surface geometric asymmetry is due to AAA bending. On average, AAA surface area increased by 56% and abdominal aortic length increased by 27% over those for the normal aorta. Our results indicate that AAA surface geometry is highly complex and cannot be simulated by simple axisymmetric models, and suggests an equally complex wall stress distribution.

Aorta, Abdominal↗

PubMed2004

Contrast sensitivity loss with aging: sampling efficiency and equivalent noise at different spatial frequencies.

The relative contributions of optical and neural factors to the decrease in visual function with aging were investigated by measurement of contrast detection at three different spatial frequencies, in the presence of external noise, on young and older subjects. Contrast detection in noise functions allows two parameters to be measured: sampling efficiency, which indicates neural changes, and equivalent noise, which demonstrates optical effects. Contrast thresholds were measured in the presence of four levels (including zero) of externally added visual noise. Measurements were obtained from eight young and eight older visually normal observers. Compared with young subjects, older subjects showed significantly (p < 0.05) lower sampling efficiencies at spatial frequencies of 1 and 4 cycles per degree (c/deg) and significantly higher equivalent noise levels for gratings of 10 c/deg. Neural and optical factors affect contrast sensitivity loss with aging differently, depending on the spatial frequency tested, implying the existence of different mechanisms.

Journal Article↗

PubMed2004

[Statistical methods to analyze risk with spatial distribution patterns].

The development of the geographic information systems has improved the interest in analyzing the characteristics of the population, taking into account the place where they live. The health of the population, measured as the risk of morbidity or mortality, is conditioned by the variety of risk factors characteristic of the region which cannot be measured. Analysis of spatial models considers the dependence of the health indicators between close regions. This dependence is due to the existence of the risk factors that are not measured but are shared by the region. Thus, the spatial distribution of these indicators depends on the geographic pattern of these risk factors. In this study, some limitations of the standardized methods and the Poisson regression used to model the spatiality are discussed and the advantages of the spatial models are shown. The methodology is illustrated by the insulin-dependent diabetes type 1 data from Catalonia during 1989 and 1998.

Demography↗

PubMed1978

Children's use of spatial prepositions in two- and three-dimensional tasks.

This study evaluates children's performance on selected spatial prepositions and determines the age levels these prepositions are acquired in both receptive and expresive language, as revealed in tasks involving both two- and three-dimensional objects. Subjects were 80 children (40 males and 40 females), ranging in age from three years to four years and eleven months. All were native English speakers with no speech, hearing, or neurological disorders, and with normal intelligence. Results indicated a significant difference in test scores according to age (older children perform better than younger), task (comprehension scores higher than production scores), referent (three-dimensional tasks showing higher scores than two-dimensional tasks), and preposition. Children's use of selected spatial prepositions is dependent on the semantic complexity of the preposition. Prepositions whose meanings can be described in terms of simple topological notions are understood and used with greater facility than those involving dimensional or Euclidean spatial notions. When the prepositional variable interacts with age, dimension, task, age + dimension, age + task, dimension + task, and age + dimension + task, overall differential response are likely to occur.

Age Factors↗

PubMed2002

Cognition in a patient with very mild right-sided hemiparkinsonism.

Non-demented patients with Parkinson's disease (PD), especially if they are high functioning and early in the course of their disease, usually exhibit mild deficits in anterograde recall memory for verbal and non-verbal material, visuospatial reasoning, visuomotor construction, temporal ordering and sequencing. Impairments in problem solving and verbal fluency tests may also occur. PD patients with predominantly right-sided symptoms usually exhibit more severe difficulties with verbal than with non-verbal tasks. We report a case of a highly educated right-handed man with very mild right-sided hemiparkinsonism who never received anti-Parkinsonian or other psychoactive medication. Our patient showed anterograde and retrograde amnesia for faces and spatial locations and difficulties on complex visuospatial tasks that required manual responses, but normal to above average performance on all other cognitive tests. The specific pattern of cognitive loss early in PD may depend on which spatial, facial or verbal pre-frontal striatal circuits are deprived of their dopaminergic inputs.

Aged↗

PubMed1987

Measurement of cytoplasmic free Ca2+ concentration in bovine tracheal smooth muscle using aequorin.

The cytoplasmic free Ca2+ concentration in bovine tracheal smooth muscle strips was measured using aequorin. Carbachol induces a rapid rise in aequorin luminescence, which reaches a peak within 1-2 min and then falls to a plateau level in 5-6 min. This plateau gradually declines but remains significantly above the base-line value after 2 h. The initial Ca2+ transient is due to Ca2+ mobilization from an intracellular caffeine-sensitive pool. The plateau appears to be due to Ca2+ influx. Histamine or 5-hydroxytryptamine (serotonin) also induce a Ca2+ transient followed by a plateau phase which is lower than that induced by carbachol. The isometric tension generated by either of these two agonists shows a gradual decline in contrast to the sustained plateau seen in the carbachol-induced contraction. Extracellular high K+ induces a dose-dependent increase in aequorin luminescence that is totally due to Ca2+ influx across the plasma membrane and is greatly inhibited by a Ca2+-channel antagonist, nimodipine. These results suggest that two temporally and spatially different Ca2+-dependent mechanisms are involved in carbachol-induced tracheal smooth muscle contraction.

Aequorin↗

PubMed1978

Possible role of transient and sustained visual mechanisms in the determination of similarity judgments.

Two studies examined the role played by transient and sustained visual mechanisms in the determination of similarity judgments produced in response to pairs of geometrical stimuli. In two experiments, subjects were trained to attend to two dimensions of a set of stimuli and to assign similarity ratings with respect to those two dimensions only. An INDSCAL multidimensional scaling analysis of the subsequent similarity ratings showed that subjects emphasized global blob, or low spatial frequency-dependent, dimensions of the stimuli when they were presented for brief durations (20 msec.), irrespective of the dimensions to which the subjects and had been trained to attend. This finding suggested that low spatial frequency selective transient mechanisms dominated the perceptual processes which underlie the similarity judgments. When the stimulus duration was raised to 50 msec. so that sustained mechanisms could also make a signficicant contribution to the perceptual processes underlying the similarity judgments, subjects emphasized only those dimensions on which they had been trained. The implications of the present findings for the concepts of selective attention and automatic activation were discussed.

Attention↗

PubMed2001

Age-dependent cognitive deficits and neuronal apoptosis in cyclooxygenase-2 transgenic mice.

The cyclooxygenases catalyze the rate-limiting step in the formation of prostaglandins from arachidonic acid and are the pharmacological targets of (NSAIDs). In brain, cyclooxygenase-2 (COX-2), the inducible isoform of cyclooxygenase, is selectively expressed in neurons of the cerebral cortex, hippocampus, and amygdala. As an immediate-early gene, COX-2 is dramatically and transiently induced in these neurons in response to NMDA receptor activation. In models of acute excitotoxic neuronal injury, elevated and sustained levels of COX-2 have been shown to promote neuronal apoptosis, indicating that upregulated COX-2 activity is injurious to neurons. COX-2 may also contribute to the development of Alzheimer's disease, for which early administration of NSAIDs is protective against development of the disease. To test the effect of constitutively elevated neuronal COX-2, transgenic mice were generated that overexpressed COX-2 in neurons and produced elevated levels of prostaglandins in brain. In cross-sectional behavioral studies, COX-2 transgenic mice developed an age-dependent deficit in spatial memory at 12 and 20 months but not at 7 months and a deficit in aversive behavior at 20 months of age. These behavioral changes were associated with a parallel age-dependent increase in neuronal apoptosis occurring at 14 and 22 months but not at 8 months of age and astrocytic activation at 24 months of age. These findings suggest that neuronal COX-2 may contribute to the pathophysiology of age-related diseases such as Alzheimer's disease by promoting memory dysfunction, neuronal apoptosis, and astrocytic activation in an age-dependent manner.

Aging↗

PubMed2006

Object perception impairments predict instrumental activities of daily living dependence in Alzheimer's disease.

This study examined the contribution of object perception and spatial localization to functional dependence among Alzheimer's disease (AD) patients. Forty patients with probable AD completed measures assessing verbal recognition memory, working memory, object perception, spatial localization, semantic knowledge, and global cognition. Primary caregivers completed a measure of activities of daily living (ADLs) that included instrumental and basic self-care subscales (i.e., IADLs and BADLs, respectively). Stepwise multiple regressions revealed that global cognition accounted for significant portions of variance among the ADL total, IADL, and BADL scores. However, when global cognition was removed from the model, object perception was the only significant cognitive predictor of the ADL total and IADL subscale scores, accounting for 18.5% and 19.3% of the variance, respectively. When considering multiple cognitive components simultaneously, object perception and the integrity of the inferotemporal cortex is important in the completion of functional abilities in general and IADLs in particular among AD patients.

Activities of Daily Living↗

PubMed2005

Spatial memory in aged rats is related to PKCgamma-dependent G-protein coupling of the M1 receptor.

In the present study, individual differences in spatial memory in aged Fischer 344 (F344) rats were associated with the extent of G-protein coupling of the M1 muscarinic receptor and the dendritic-to-somal ratio of hippocampal PKCgamma (d/sPKCgamma) immunogenicity. Following testing in the eight-arm radial maze task, 7 young and 13 aged rat brains were sectioned through the dorsal hippocampal formation (HF). G-protein coupling of the M1 receptor was assessed autoradiographically using competition binding studies in the presence and absence of a G-protein uncoupler to determine high (K(H)) and low (K(L)) affinity states for agonist in the HF, neocortex, and amygdala. In aged animals, a relationship between choice accuracy in the maze and K(H), a measure of M1 receptor-G-protein coupling was seen in the dentate gyrus, CA3, CA1, and neocortex. Furthermore, choice accuracy and d/sPKCgamma immunogenicity showed a significant relationship in CA1. Lastly, a correlation was seen in the CA1 of aged animals between K(H) and d/sPKCgamma. These relationships did not hold for the amygdala. Thus, individual differences in a naturally occurring age-dependent disruption of cholinergic-PKCgamma signal transduction is associated with spatial memory dysfunction.

Age Factors↗

PubMed2003

Selective elimination of corticogeniculate feedback abolishes the electroencephalogram dependence of primary visual cortical receptive fields and reduces their spatial specificity.

The role of corticogeniculate feedback in the organization, function, and state dependence of visual responses and receptive fields (RFs) is not well understood. We investigated the contribution of the corticogeniculate loop to state-dependent changes of characteristics of the primary visual cortex response by using a novel approach of eliminating corticogeniculate projection neurons with targeted neuronal apoptosis. Experiments were performed in anesthetized cats (N2O plus halothane) with parallel recordings of single units from experimental (right) and control (left) hemispheres approximately 2 weeks after induction of apoptosis. Within the experimental hemispheres, neurons of area 17 and of the dorsal lateral geniculate nucleus (dLGN) showed an unusually enhanced and prolonged tonic visual response during episodes of synchronized (syn) EEG activity, whereas response levels during less synchronized states were almost normal. In addition, dLGN cells showed a reduced tendency for burst firing and a less regular spike interval distribution compared with those of controls. These changes are likely attributable to a tonic depolarization of dLGN relay neurons or, more likely, to a decreased responsiveness of thalamic inhibitory processes to cortical feedback. Cortical neurons also displayed an activity-dependent increase in RF size, in contrast to an almost activity-invariant RF size of controls, a phenomenon likely related to the elimination of collateral, intracortical projections of layer 6 neurons. Together, these results demonstrate that selective chronic elimination of corticogeniculate feedback results in the loss of EEG-correlated differences of visual processing in the remaining thalamocortical network, accompanied by a significant increase in excitability during syn EEG, at the expense of noticeably reduced spatial receptive-field specificity in the remaining cortical neurons.

Action Potentials↗

PubMed1999

Depth aliasing by the transient-stereopsis system.

A fundamental problem in stereo-processing is determining which images in the two eyes correspond to the same object. This problem is particularly pronounced with periodic stimuli where it is theoretically possible to binocularly match a given feature in one eye with any of the identical features in the other eye. One way to minimise the likelihood of the occurrence of such aliasing is to restrict the upper-disparity limit that a particular binocular cell can process to one-half of the spatial period to which the cell is sensitive. While such a restriction would not be a major problem for the sustained stereo-system (which processes small disparities) it would be for the transient system (which is capable of processing disparities as large as 10 degrees). Large-field sinewave variations in luminance were used to compare the propensity of the sustained and transient systems to exhibit depth aliasing--that is to signal a depth sign that corresponds to a binocular match that is greater than the nearest-neighbour pairing. Results were that: depth aliasing was exhibited at short, but not at long durations; decreasing the disparity of the stimulus reduced the likelihood of depth-aliasing; and the critical disparity for this reduction in depth aliasing was dependent upon the spatial frequency of the stimulus, i.e. it was phase, not absolute disparity dependent. Based upon these results, we conclude that while the sustained system implements the half-cycle disparity-processing limit, the transient system does not.

Depth Perception↗

PubMed2004

Engineering the morphology and electrophysiological parameters of cultured neurons by microfluidic surface patterning.

The ability to control the orientation, morphology, and electrophysiological characteristics of neurons in culture allows the construction of neural circuits with defined physiological properties. Using microfluidic protein deposition onto chemically modified glass, we achieve the controlled growth of Aplysia neurons on geometrical patterns of poly-L-lysine and collagen IV, surrounded by nonadhesive regions of bovine albumin. We investigate the parameters essential for forming functional neuronal networks, the morphology, biochemistry, and electrophysiology under engineered cell culture conditions. We demonstrate that not only the orientation of neurite extension but also the number of primary neurites originating from the cell soma, their length, and branching pattern depend on the spatial constraints presented by the size and shape of the adhesion region on the patterned substrate. In addition, the physicochemical properties of the support layer influence the electrical activity of the cultured neurons. Substrate-dependent changes in the amplitude and in the dynamic parameters of the action potential cause decreased spike broadening in patterned neurons, which reflects changes in the number or functioning of active membrane ion channels. In contrast to morphology and electrophysiology, the neuropeptide content, as determined by mass spectrometry of individual patterned neurons, is not affected by the growth on patterned surfaces. Our results suggest that the morphological and electrophysiological parameters of neurons can be predictably altered/engineered by modulation of the chemical, physical, and topographical features of culture substrates. We also demonstrate that a full suite of techniques is required for functional characterization of neurons on engineered substrates.

Action Potentials↗

PubMed1996

NMDA receptor antagonists impair prefrontal cortex function as assessed via spatial delayed alternation performance in rats: modulation by dopamine.

The present study was performed to assess the role of excitatory amino acid and dopamine receptors on associative functions of the prefrontal cortex (PFC) of the rat. Spatial delayed alternation was used as a PFC-sensitive cognitive task. In addition, in vivo microdialysis was used to assess the release of dopamine in the PFC. The noncompetitive NMDA antagonists ketamine (10-30 mg/kg) and MK-801 (0.1 and 0.5 mg/kg) dose-dependently impaired the spatial delayed alternation performance compared with the saline-treated control group. Administration of the dopamine antagonists raclopride (0.1 and 0.5 mg/kg), SCH-23390 (0.1 mg/kg), or haloperidol (0.1 mg/kg) was without a significant effect. However, haloperidol and raclopride (but not SCH-23390) reversed the disruptive effect of 30 mg/kg ketamine on spatial delayed alternation performance. Microdialysis studies revealed that this dose of ketamine preferentially increased the release of dopamine in the PFC compared with the striatum. These findings indicate that attenuation of glutamatergic neurotransmission at the NMDA receptor impairs PFC-dependent cognitive functions. Furthermore, activation of dopamine neurotransmission contributes, at least in part, to this impairment.

Animals↗

PubMed1997

The Craik-O'Brien-Cornsweet illusion in colour: quantitative characterisation and comparison with luminance.

The strength of the Craik-O'Brien-Cornsweet illusion was measured for different values of spatial and temporal stimulus parameters, in the traditional achromatic version, and in an isoluminant colour version. It was found that the illusion is much weaker with isoluminant colour stimuli than with achromatic luminance stimuli. The illusion depends on the spatial parameters of the stimulus in a way that yields an approximate scale invariance: The strength of the illusion is similar for different stimulus sizes, as long as the ratio of the width of the transition region around the edge, where luminance or colour change, to the total stimulus width is preserved. In both the achromatic and the chromatic case, the strength of the illusion decreases with increasing presentation time. The similarity of the differences between brightness and colour effects on one hand and the differences in sensitivity for colour and luminance changes in humans on the other suggests that a lack of gradient detection underlies the Craik-O'Brien-Cornsweet illusion.

Color Perception↗

PubMed2004

Spatial memory, recognition memory, and the hippocampus.

There is wide agreement that spatial memory is dependent on the integrity of the hippocampus, but the importance of the hippocampus for nonspatial tasks, including tasks of object recognition memory is not as clear. We examined the relationship between hippocampal lesion size and both spatial memory and object recognition memory in rats. Spatial memory was impaired after bilateral dorsal hippocampal lesions that encompassed 30-50% total volume, and as lesion size increased from 50% to approximately 100% of total hippocampal volume, performance was similarly impaired. In contrast, object recognition was intact after dorsal hippocampal lesions that damaged 50-75% of total hippocampal volume and was impaired only after larger lesions that encompassed 75-100% of hippocampal volume. Last, ventral hippocampal lesions that encompassed approximately 50% of total hippocampal volume impaired spatial memory but did not affect object recognition memory. These findings show that the hippocampus is important for both spatial memory and recognition memory. However, spatial memory performance requires more hippocampal tissue than does recognition memory.

Animals↗

PubMed2002

Inhibition of cyclin-dependent kinases improves CA1 neuronal survival and behavioral performance after global ischemia in the rat.

Increasing evidence suggests that cyclin-dependent kinases participate in neuronal death induced by multiple stresses in vitro. However, their role in cell death paradigms in vivo is not well characterized. Accordingly, the authors examined whether cyclin-dependent kinase inhibition resulted in functionally relevant and sustained neuroprotection in a model of global ischemia. Intracerebroventricular administration of the cyclin-dependent kinase inhibitor flavopiridol, immediately or at 4 hours postreperfusion after a global insult, reduced injury in the CA1 of the hippocampus when examined 7 days after reperfusion. No significant protection was observed when flavopiridol was administered 8 hours after reperfusion. The tumor-suppressor retinoblastoma protein, a substrate of cyclin-dependent kinase, was phosphorylated on a cyclin-dependent kinase consensus site after the global insult; this phosphorylation was inhibited by flavopiridol administration. Importantly, flavopiridol had no effect on core body temperature, suggesting that the mechanism of neuroprotection was through cyclin-dependent kinase inhibition but not through hypothermia. Furthermore, inhibition of cyclin-dependent kinases improved spatial learning behavior as assessed by the Morris water maze 7 to 9 days after reperfusion. However, the histologic protection observed at day 7 was absent 28 days after reperfusion. These results indicate that cyclin-dependent kinase inhibition provides an extended period of morphologic and functional neuroprotection that may allow time for other neuroprotective modalities to be introduced.

Animals↗

PubMed2002

Adaptation of spatiotemporal mechanisms by increment and decrement stimuli.

Sawtooth modulation has been used in the past to examine visual sensitivity to luminance increments and decrements. The threshold elevation caused by adaptation depends on the spatial profile of the stimulus field and the polarities of the adaptation and test stimuli. We hypothesized that the adaptation effects reflect a change in the sensitivity of the spatiotemporal channels that detect the stimuli. We used a 2-deg disk centered in a larger surround field. Five levels of contrast between the test field and surround were investigated: equiluminant, three intermediate levels, and dark. At each contrast, observers adapted for 5 s to 2-Hz sawtooth modulation (rapid-on or rapid-off). Immediately after adaptation, thresholds were measured for detection of a single cycle of either a rapid-on or a rapid-off waveform. Varying the contrast of the surround affected observers' sensitivity to the polarity of the sawtooth stimulus to the extent that the pattern of sensitivity with the equiluminant surround was the opposite of that with the dark surround. To examine temporal factors, we measured thresholds for slow (500-ms ramps) and fast (8.3-ms pulses) test stimuli. The adaptation effect was preserved with the ramp stimuli but not with the pulse stimuli. Blurring the edge between the test and surround fields in the equiluminant surround condition raised thresholds for all sawtooth test stimuli, suggesting that spatiotemporal channels sensitive to high spatial frequencies and low temporal frequencies facilitate detection in that condition. These findings suggest that adaptation to sawtooth modulation can differentially effect the sensitivity of ON and OFF pathways, but the relative desensitization of each pathway depends on an interaction with the adaptation state of spatiotemporal channels that are involved in detection.

Adaptation, Physiological↗