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PubMed2006

Is high-spatial frequency information used in the early stages of face detection?

The present study examined the role of high-spatial frequency information in early face processing, as indexed by the N170 face-sensitive ERP component. Participants detected 4 versions of famous faces, including full spectrum faces, and bandpass filtered faces containing predominantly high-spatial frequencies, low-spatial frequencies or both. The power spectra of all stimuli were balanced by superimposing the faces onto a visual noise background that included the spatial frequency information that was missing in filtered faces, e.g., high-spatial frequency faces were presented on a high- and low-spatial frequency background. An additional condition comprising of filtered visual noise only was also created to ensure that any observed effects were related to the processing of faces and not simply due to variations between spatial frequency information. Both behavioral and electrophysiological results replicated previous findings of a low-spatial frequency advantage for face processing. However, our results also show that faces containing both high and low-spatial frequency information are detected faster and more accurately than faces containing predominantly low-spatial frequencies. Furthermore, this advantage occurred with an enhanced amplitude of the N170. Together, these findings refute the suggestion that high-spatial frequencies are redundant in face perception.

Adult↗
PubMed2004

Binocular fusion/suppression to spatial frequency differences at the border of areas 17/18 of the cat.

As shown by various human psychophysical studies, interocular spatial frequency disparities can yield a variety of percepts. In order to examine how binocular fusion is affected by spatial frequency differences, we have recorded cells in the border region of areas 17/18 of anesthetized cats. The optic axes of the eyes were deviated onto cathode-ray screens, and the optimal spatial frequency of each eye was assessed by monocular stimulations using drifting sinusoidal gratings. The optimal relative phase using identical spatial frequencies in both eyes was first determined. Spatial frequency differences were then introduced by keeping the optimal spatial frequency constant in one eye and varying the spatial frequency in the other. Results indicate that cells (39%) responded with an increased firing rate (facilitation) to similar spatial frequencies in each eye and with a gradual attenuation (occlusion or suppression) when spatial frequency differences were increased. However, binocular facilitation did not always occur to the presentation of identical stimuli. For 16% of the cells, maximal responses were observed when lower spatial frequencies than the optimal one were presented in one eye while higher spatial frequencies produced suppression. The opposite pattern was observed only for two cells. These findings are discussed in terms of binocular fusion and suppression.

Animals↗
PubMed2006

Dynamic distribution of Spatial during mouse spermatogenesis and its interaction with the kinesin KIF17b.

The Spatial gene is expressed in highly polarized cell types, such as epithelial cells in the thymus, neurons in the brain and germ cells in the testis. In this study, we report the characterization and distribution of Spatial proteins during mouse spermatogenesis. Besides Spatial-epsilon and -delta, we show that the newly described short isoform Spatial-beta is expressed specifically in round spermatids. Using indirect immunofluorescence, we detected Spatial in the cytosol of the early round spermatid. By the end stages of round spermatids, Spatial is concentrated at the opposite face of the acrosome near the nascent flagellum and in the manchette during the elongation process. Finally in mature sperm, Spatial persists in the principal piece of the tail. Moreover, we found that Spatial colocalizes with KIF17b, a testis-specific isoform of the brain kinesin-2 motor KIF17. This colocalization is restricted to the manchette and the principal piece of the sperm tail. Further, coimmunoprecipitation experiments of native proteins from testis lysates confirmed Spatial-KIF17b association through the long Spatial-epsilon isoform. Together, these findings imply a function of Spatial in spermatid differentiation as a new cargo of kinesin KIF17b, in a microtubule-dependent mechanism specific to the manchette and the principal piece of the sperm tail.

Animals↗
PubMed2002

Spatial-frequency characteristics of letter identification in central and peripheral vision.

Spatial-frequency characteristics of letter identification are much better understood in the fovea than in the periphery. The purpose of this study was to compare the spatial-frequency characteristics of letter identification in central and peripheral vision. We measured contrast thresholds for identifying single, Times-Roman lower-case letters that were spatially band-pass filtered. Each of the 26 letters was digitally filtered with a set of nine cosine log filters, with peak object spatial frequencies ranging from 0.63 to 10 c/letter, in half-octave steps. Bandwidth of the filters was 1 octave. Three observers with normal vision were each tested monocularly at the fovea, and at 5 degrees and 10 degrees in the inferior visual field. Letter sizes were 0.2, 0.4 and 0.6 log units larger than high contrast, unfiltered acuity letters. Plots of contrast sensitivity for letter identification vs. frequency of the band-pass filters exhibit spatial tuning. In general, the spatial-frequency characteristics of letter identification are fundamentally identical between central and peripheral vision. These characteristics include the scaling of the peak frequency of the spatial-tuning functions with letter size and the bandwidth of the tuning functions. The only difference between the fovea and the periphery is that for the same physical letter size, peak sensitivity of the spatial-tuning functions occurs at a higher retinal frequency at the fovea than in the periphery. To test whether or not the contrast sensitivity function (CSF) can account for the differences in the spatial-frequency characteristics of letter identification between central and peripheral vision, we incorporated a human CSF into an ideal-observer model, and tested the performance of this ideal-observer on the same letter identification task used with the human observers. Data from this CSF-ideal-observer resemble closely those of human observers, suggesting that the spatial-frequency characteristics of human letter identification can be accounted for by the CSF and the letter-identity information, without invoking selection among narrow-band spatial-frequency channels.

Contrast Sensitivity↗
PubMed2000

Spatial correlation analysis of atrial activation patterns during sustained atrial fibrillation in conscious goats.

In this study we applied both linear and nonlinear spatial correlation measures to characterize epicardial activation patterns of sustained atrial fibrillation in instrumented conscious goats. It was investigated if nonlinearity was involved in the spatial coupling of atrial regions and to what extent fibrillation was organized in the experimental model of sustained atrial fibrillation (AF) in instrumented goats. Data were collected in five goats during experiments to convert AF by continuous infusion of cibenzoline. Spatial organization during AF was quantified with the linear spatial cross correlation function and the nonlinear spatial cross redundancy which was calculated using the Grassberger-Procaccia correlation integral. Two different types of correlation were evaluated to distinguish simultaneous interaction from non-simultaneous interaction, for instance resulting from propagation of fibrillation waves. The nonlinear association length and the linear correlation length were estimated along the principal axes of iso-correlation contours in two-dimensional correlation maps of the nonlinear spatial redundancy and the linear spatial correlation function, respectively. To quantitatively assess the degree of nonlinearity, the association length was also estimated from the linearized spatial redundancy using multivariate surrogate data. The differences between the nonlinear and linearized association lengths indicated that a nonlinear component in the spatial organization of AF predominantly existed in the right atrium. The degree of organization characterized by association length along the short principal axis was higher in the right atrium (15 +/- 7 mm) than in the left atrium (8 +/- 4 mm). The spatial extension of coherent atrial patches was estimated from a surface of association equal to the area spanned by the principal axes of iso-correlation contours from the redundancy, including the effects from non-simultaneous interaction. Interpreting this area as the spatial domain of a fibrillation wavelet, the results suggest that the mapped region was activated on average by two wavelets in the left atrium and by one wavelet in the right atrium. Therefore, the activation pattern of sustained AF in goats was relatively organized, consistent with type II of AF. It is suggested that the surface of association is a measure of the number of independent wavelets present in the atria during sustained AF, and that larger association lengths result from fewer and larger reentrant circuits.

Animals↗
PubMed2003

Coronary calcium scoring: modelling, predicting and correcting for the effect of CT scanner spatial resolution on Agatston and volume scores.

The purpose of this study was to evaluate the impact of spatial resolution on coronary calcium scoring by x-ray CT, to assess the scoring performance of different CT scanners as they are operated in the field and to correct for the effects of CT scanner spatial resolution on coronary calcium scoring. A phantom consisting of five aluminium wires of known diameter in water was used to measure spatial resolution and to assess scoring performance. Fourteen CT scanners (three helical, two dual, two electron-beam and seven multi-detector) from four manufacturers were evaluated, some under different operating conditions. One scanner was monitored over a 3 month period and again 6 months later. Both spatial resolution and image pixel size significantly affect calcium scoring results. Spatial resolution can be measured with a precision of about 2%. Scanner spatial resolution ranged from 1 to 1.7 mm full-width-half-maximum (FWHM), and pixel size from 0.25 to 0.86 mm. Spatial resolution differences introduce systematic scoring differences that range from 38% to 1100% depending on wire size. Significant temporal variations in spatial resolution were observed in the monitored scanner. By correcting all the scanners to the same target spatial resolution, the standard deviation of individual scanners with respect to a mean value (the spread) can be reduced by 25-70% for different wires. In conclusion, scanner spatial resolution significantly affects calcium scoring and should be controlled for. Scanner performance can change over time. Under ideal conditions, CT scanners should be operated with a standard spatial resolution for calcium scoring. When this is not possible, post-processing correction is a viable alternative.

Arteriosclerosis↗
PubMed2005

Clonal and spatial genetic structures of aspen (Populus tremuloides Michx.).

To portray aspen clonal and spatial genetic structures, we mapped and genotyped trees in two 1-ha plots, each containing three aspen cohorts originating from fire or subsequent secondary disturbances. We used four microsatellite loci to identify aspen clones and increment core analysis to determine tree age. Clonal dimensions were measured by the maximum distance between two ramets and the number of ramets per genet. Standard normal deviate (SND) was used to assess the spatial distribution of aspen genets and cohorts, and multivariate spatial genetic autocorrelations to assess the spatial distribution of aspen genetic variation. Most aspen genets consisted of only one ramet (> 75%). Median clonal dimensions were 19 and 29 m (maxima: 104 and 72 m in the two plots). No segregation was observed between clones. Aspen cohorts were spatially segregated but trees were spatially aggregated within old and medium-aged cohorts. In contrast, trees were more randomly distributed within the youngest cohorts. This coincided with a spatial genetic autocorrelation at small scales (up to 30 m) in the older cohorts and a more random genetic distribution in the youngest ones. Our results suggest that aspen spatial genetic structuring reflects the spatial patterns produced by the regeneration of discrete cohorts at different stages of succession. Vegetative reproduction leads to aspen genetic spatial structuring at small scales (few metres) until midsuccession. However, as the stand gets older, the spatial distribution of aspen trees and genetic structure evolve from a structured pattern to a more random one under a gap disturbances regime.

Clone Cells↗
PubMed1978

Spatial summation in the receptive fields of simple cells in the cat's striate cortex.

1. We have examined the responses of simple cells in the cat's atriate cortex to visual patterns that were designed to reveal the extent to which these cells may be considered to sum light-evoked influences linearly across their receptive fields. We used one-dimensional luminance-modulated bars and grating as stimuli; their orientation was always the same as the preferred orientation of the neurone under study. The stimuli were presented on an oscilloscope screen by a digital computer, which also accumulated neuronal responses and controlled a randomized sequence of stimulus presentations. 2. The majority of simple cells respond to sinusoidal gratings that are moving or whose contrast is modulated in time in a manner consistent with the hypothesis that they have linear spatial summation. Their responses to moving gratings of all spatial frequencies are modulated in synchrony with the passage of the gratings' bars across their receptive fields, and they do not produce unmodulated responses even at the highest spatial frequencies. Many of these cells respond to temporally modulated stationary gratings simply by changing their response amplitude sinusoidally as the spatial phase of the grating the grating is varied. Nonetheless, their behavior appears to indicate linear spatial summation, since we show in an Appendix that the absence of a 'null' phase in a visual neurone need not indicate non-linear spatial summation, and further that a linear neurone lacking a 'null' phase should give responses of the form that we have observed in this type of simple cell. 3. A minority of simple cells appears to have significant non-linearities of spatial summation. These neurones respond to moving gratings of high spatial frequency with a partially or totally unmodulated elevation of firing rate. They have no 'null' phases when tested with stationary gratings, and reveal their non-linearity by giving responses to gratings of some spatial phases that are composed partly or wholly of even harmonics of the stimulus frequency ('on-off' responses). 4. We compared simple receptive fields with their sensitivity to sinusoidal gratings of different spatial frequencies. Qualitatively, the most sensitive subregions of simple cells' receptive fields are roughly the same width as the individual bars of the gratings to which they are most sensitive. Quantitatively, their receptive field profiles measured with thin stationary lines, agree well with predicted profiles derived by Fourier synthesis of their spatial frequency tuning curves.

Action Potentials↗
PubMed1978

Spatial and temporal contrast sensitivity of neurones in areas 17 and 18 of the cat's visual cortex.

1. We have examined the spatial and temporal tuning properties of 238 cortical neurones, recorded using conventional techniques from acutely prepared anaesthetized cats. We determined spatial and temporal frequency tuning curves using sinusoidal grating stimuli presented to each neurone's receptive field by a digital computer on a cathode ray tube. 2. We measured tuning curves either by determining response amplitude as a function of spatial or temporal frequency, or by measuring contrast sensitivity (the inverse of the contrast of the grating that just elicited a detectable response). The two measures give very similar tuning curves in all cases. 3. We recorded from 184 neurones in area 17; of these 156 had receptive fields within 5 degrees of the area centralis. The range of preferred spatial frequency for these neurones was 0.3--3 c/deg, and their spatial frequency tuning band widths varied from 0.7 to 3.2 octaves at half-amplitude. The most common band width was roughly 1.3 octaves. Simple and complex cells in area 17 did not differ in their distributions of preferred spatial frequency, although complex cells were, on average, slightly less selective for spatial frequency than simple cells. 4. We recorded from fifty-four neurones from area 18, and performed several experiments in which we recorded from corresponding portions of both area 17 and area 18 in the same electrode penetration. Neurones in area 18 preferred spatial frequencies that were, on average, one third as high as those preferred by area 17 neurones at the same retinal eccentricity. Thus the range of preferred spatial frequency in area eighteen cells having receptive fields within 5 deg of the area centralis was between less than 0.1 and 0.5 c/deg. The distributions of optimum spatial frequency in the two areas were practically non-overlapping at eccentricities as high as 15 deg, the greatest eccentricity we examined. Neurones in area 18 were about as selective for spatial frequency as were neurones in area 17. 5. We determined temporal frequency tuning characteristics for some neurones from each area, using gratings that moved steadily across the screen. Neurones from area 17 all responded well to low temporal frequencies, and less well to higher frequencies (in excess of, usually, 2 or 4 Hz). In contrast, neurones recorded from area 18 sometimes had similar tuning properties, but more commonly showed a pronounced reduction in response as the temporal frequency was moved either above or below some optimum value (usually 2--8 Hz). 6. We conclude from these results that areas 17 and 18 act in parallel to process different aspects of the visual information relayed from the retina via the lateral geniculate complex. Some or all of the differences between the areas may be attributable to the predominance of Y cell input to area 18 and the predominance of X cell input to area 17...

Action Potentials↗
PubMed1983

Spatial-frequency-specific inhibition in cat striate cortex cells.

Responses to single and multiple spatial frequency gratings were recorded from eighty-eight cat striate cortex cells. A cell's response to a grating of its optimum spatial frequency (f) was examined both alone and in the presence of gratings of 1/4, 1/3, 1/2, 2, 3 and 4f, respectively. Some 97% (thirty-seven of thirty-eight) of all simple cells showed significant inhibition of f by one or more of the other frequencies. This inhibition was usually fairly narrowly tuned, with only one or two spatial frequencies producing significant inhibition. Thirty-four simple cells were maximally inhibited by a higher frequency, three by a lower spatial frequency. By far the most common interaction was a considerable inhibition of f by 2f and/or 3f. Of the thirty-seven simple cells showing inhibition to a complex grating, seventeen responded in a manner dependent on the relative phases of the two components. Some showed only inhibition of f; in others, the response to f was either increased or decreased, depending on the relative phase of the two frequencies. The other twenty simple cells showed phase-independent inhibition: the inhibition was of approximately equal amplitude regardless of the relative phase angle of the two grating components. Such phase-independent inhibition cannot be accounted for by linear summation within classical cortical receptive fields. Only eighteen of forty-eight (38%) of the complex cells showed significant inhibition of f by one or more other spatial frequencies. Fourteen of these (29%) were maximally inhibited by a higher spatial frequency, four (8%) by a lower spatial frequency. Inhibitory interactions in complex cells were never dependent on the relative phase of the two component gratings. Six simple cells (16%) and fourteen complex cells (29%) showed significant facilitation of the response to f by one or more (most often lower) spatial frequencies. This enhanced response was greater than the sum of the responses to each component alone, was usually broadly tuned for spatial frequency, and did not depend on the relative phase of the two components. It thus differs from the increased response sometimes seen in a phase-dependent interaction. Some of the observed spatial-frequency-specific interactions are incompatible with either a strictly hierarchical model of cortical architecture or a simple linear filter model of visual cortical processing. The asymmetry of inhibition suggests that it subserves some function other than (or in addition to) the narrowing of spatial frequency tuning functions.

Action Potentials↗
PubMed1983

Spatial contrast sensitivities of X and Y type neurones in the cat's dorsal lateral geniculate nucleus.

The discharges of X and Y type neurones were recorded extracellularly from the binocular segment of the A laminae of the dorsal lateral geniculate nucleus of anaesthetized, paralysed cats. X type geniculate cells are referred to as XG cells and Y type geniculate cells as YG cells. They were differentiated on the basis of a test of linear spatial summation and the relatively higher spatial resolution of the XG type. Contrast sensitivities of these cells were measured for a series of spatial frequencies at 5.2 Hz. Sensitivity measurements took account of the variability inherent in the cells' maintained discharges. Maintained discharges of XG and YG cells were found to be similarly noisy and the level of noise was stable in the time range of seconds to hours. The noise level was greater than in corresponding ganglion cells, suggesting that an extra source of noise is added at the geniculate level. The criterion set routinely to measure 'threshold' contrast corresponded to a level of reliability of about two false positives in fifty. YG cells had higher contrast sensitivities at low spatial frequencies and XG at high. YG cells were found also to have higher peak sensitivities. The optimum spatial frequency of XG cells was found to be higher than that of YG cells. YG cells also show less attenuation in contrast sensitivity for gratings of spatial frequencies below their optima. Contrast sensitivities of both XG and YG cells were found to be lower than those of corresponding ganglion cells. The optimum spatial frequencies and spatial resolutions of XG and YG cells decreased as the retinal eccentricities of their receptive fields increased. XG cells were found to have higher spatial resolution in lamina A than lamina A1. No difference was found between on- and off-centre types of either cell class. Although individual YG cells are more sensitive to low spatial frequencies than individual XG cells, the ensemble of XG cells of one centre-type which overlaps a particular YG cell receptive field of the same centre-type has a contrast sensitivity at optimum spatial frequency very close to that of the YG cell. This leads one to believe that XG cells could by themselves account for the contrast sensitivity of the cat's visual system.

Animals↗
PubMed1989

Binocular interactions in the cat's dorsal lateral geniculate nucleus. I. Spatial-frequency analysis of responses of X, Y, and W cells to nondominant-eye stimulation.

1. X, Y, and W cells in the A and C layers of the cat's dorsal lateral geniculate nucleus (LGN) were tested for responses to stimulation of the nondominant eye. The main purpose was to determine the incidence of nondominant-eye excitation and inhibition among different classes of cells and to examine the spatial-frequency tuning of responses to the nondominant eye. 2. Of 198 cells that were tested with drifting sine-wave gratings presented to the nondominant eye, 109 (55%) showed statistically significant responses. Four types of responses were observed: an increase in the mean discharge rate (F0 excitation), a decrease in the mean discharge rate (F0 inhibition), an increased modulation at the fundamental frequency of the grating (F1 excitation), and a decreased modulation at the fundamental frequency of the grating (F1 inhibition). Overall, 29% of the cells responded with inhibition, 24% responded with excitation, and 2% showed both excitation and inhibition, depending upon the spatial frequency and/or the harmonic response component. The relative incidence of excitation and inhibition was similar for X, Y, and W cells, for cells with on-center and off-center receptive fields, for cells with different receptive-field eccentricities, and for cells in each LGN layer. In addition, within layers A and A1, responses were similar for cells at different distances from the laminar borders. 3. Spatial-frequency response functions indicated that cells could have band-pass or low-pass spatial-frequency tuning through the nondominant eye. Band-pass cells tended to be narrowly tuned (less than or equal to 1 octave), and low-pass cells responded to a broader range of spatial frequencies. These properties were similar for X, Y, and W cells. Spatial resolution tended to be low (less than or equal to 0.8 c/deg for most cells), although a few cells responded to the highest spatial frequency tested (5.4 c/deg). Likewise, optimal spatial frequency was low (less than or equal to 0.2 c/deg) for most cells. These properties were similar for X and Y cells, and there was a weak tendency for X and Y cells to have higher optimal spatial frequencies and spatial resolutions than W cells. 4. In terms of absolute change in activity, responses to drifting gratings were weak. However, cells that were inhibited generally showed 20-60% decreases in activity to the optimal spatial frequency, and cells that were excited generally showed 40-100% increases. Response amplitudes were similar for X, Y, and W cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2003

The modulation of simple reaction time by the spatial probability of a visual stimulus.

Simple reaction time (SRT) in response to visual stimuli can be influenced by many stimulus features. The speed and accuracy with which observers respond to a visual stimulus may be improved by prior knowledge about the stimulus location, which can be obtained by manipulating the spatial probability of the stimulus. However, when higher spatial probability is achieved by holding constant the stimulus location throughout successive trials, the resulting improvement in performance can also be due to local sensory facilitation caused by the recurrent spatial location of a visual target (position priming). The main objective of the present investigation was to quantitatively evaluate the modulation of SRT by the spatial probability structure of a visual stimulus. In two experiments the volunteers had to respond as quickly as possible to the visual target presented on a computer screen by pressing an optic key with the index finger of the dominant hand. Experiment 1 (N = 14) investigated how SRT changed as a function of both the different levels of spatial probability and the subject's explicit knowledge about the precise probability structure of visual stimulation. We found a gradual decrease in SRT with increasing spatial probability of a visual target regardless of the observer's previous knowledge concerning the spatial probability of the stimulus. Error rates, below 2%, were independent of the spatial probability structure of the visual stimulus, suggesting the absence of a speed-accuracy trade-off. Experiment 2 (N = 12) examined whether changes in SRT in response to a spatially recurrent visual target might be accounted for simply by sensory and temporally local facilitation. The findings indicated that the decrease in SRT brought about by a spatially recurrent target was associated with its spatial predictability, and could not be accounted for solely in terms of sensory priming.

Analysis of Variance↗
PubMed2005

Assessing the role of different spatial frequencies in word perception by good and poor readers.

Numerous studies indicate that dyslexic and nondyslexic individuals exhibit different patterns of sensitivity to spatial frequency. However, the extension of this effect to normal (nondyslexic) adults of good and poor reading abilities and the role played by different spatial frequencies in word perception have yet to be determined. In this study, using normal (nondyslexic) adults, we assessed reading ability, spatial frequency sensitivity, and perception of spatially filtered words and nonwords (using a two-alternative forced choice paradigm to avoid artifactual influences of nonperceptual guesswork). Good and poor readers showed different patterns of spatial frequency sensitivity. However, no differences in accuracy of word and nonword perception were found between good and poor readers, despite their differences in spatial frequency sensitivity. Indeed, both reading abilities showed the same superior perceptibility for spatially filtered words over nonwords across different spatial frequency bands. These findings indicate that spatial frequency sensitivity differences extend to normal (nondyslexic) adult readers and that a range of spatial frequencies can be used for word perception by good and poor readers. However, spatial frequency sensitivity may not accurately reveal an individual's ability to perceive words.

Humans↗
PubMed1991

Spatial disorientation in persons with early senile dementia of the Alzheimer type.

Although spatial disorientation is frequently observed in persons with Alzheimer disease, it is not well understood. A descriptive study was conducted to examine spatial skills associated with spatial orientation. Spatial tasks were selected and grouped into three types of spatial skills: perceptual, cognitive, and functional. These spatial tasks were administered to a group of 15 persons with senile dementia of the Alzheimer type (SDAT) (early Alzheimer disease) and a group of 15 control subjects. The results indicated that the subjects with SDAT were impaired on half of the perceptual spatial tasks and all of the cognitive spatial tasks. On the functional spatial tasks, however, the subjects with SDAT showed impaired skills in the new environment but intact skills in familiar environments. Spatial disorientation poses a danger and limits a person's ability to independently perform daily activities that require navigation outside of the home. Occupational therapy should therefore include the assessment of spatial orientation skills in persons who are in the early stages of dementia.

Activities of Daily Living↗
PubMed1999

Global spatial normalization of human brain using convex hulls.

UNLABELLED: Global spatial normalization transforms a brain image so that its principal global spatial features (position, orientation and dimensions) match those of a standard or atlas brain, supporting consistent analysis and referencing of brain locations. The convex hull (CH), derived from the brain's surface, was selected as the basis for automating and standardizing global spatial normalization. The accuracy and precision of CH global spatial normalization of PET and MR brain images were evaluated in normal human subjects. METHODS: Software was developed to extract CHs of brain surfaces from tomographic brain images. Pelizzari's hat-to-head least-square-error surface-fitting method was modified to fit individual CHs (hats) to a template CH (head) and calculate a nine-parameter coordinate transformation to perform spatial normalization. A template CH was refined using MR images from 12 subjects to optimize global spatial feature conformance to the 1988 Talairach Atlas brain. The template was tested in 12 additional subjects. Three major performance characteristics were evaluated: (a) quality of spatial normalization with anatomical MR images, (b) optimal threshold for PET and (c) quality of spatial normalization for functional PET images. RESULTS: As a surface model of the human brain, the CH was shown to be highly consistent across subjects and imaging modalities. In MR images (n = 24), mean errors for anterior and posterior commissures generally were <1 mm, with SDs < 1.5 mm. Mean brain-dimension errors generally were <1.3 mm, and bounding limits were within 1-2 mm of the Talairach Atlas values. The optimal threshold for defining brain boundaries in both 18F-fluorodeoxyglucose (n = 8) and 15O-water (n = 12) PET images was 40% of the brain maximum value. The accuracy of global spatial normalization of PET images was shown to be similar to that of MR images. CONCLUSION: The global features of CH-spatially normalized brain images (position, orientation and size) were consistently transformed to match the Talairach Atlas in both MR and PET images. The CH method supports intermodality and intersubject global spatial normalization of tomographic brain images.

Adult↗
PubMed2005

Spatial genetic structure of two HIV-I-resistant polymorphisms (CCR2-64 I and SDF1-3'A) alleles in population of Shandong Province, China.

OBJECTIVE: To explore the spatial genetic structure of two HIV-I-resistant polymorphisms (CCR2-64 I and SDF1-3'A) alleles in the population of Shandong Province, China. METHODS: Using the techniques of spatial stratified sampling and spatial statistics, the spatial genetic structure of the locus (CCR2-64 I and SDF1-3'A), which was shown to be important co-receptor for HIV infection, was quantified from the populations of 36 sampled counties of Shandong Province, and a total of 3147 and 3172 samples were taken for testing CCR2-64I and SDF1-3'A respectively from individuals without known history of HIV-I infection and AIDS symptoms. RESULTS: There were significantly spatial genetic structures of the two alleles at different spatial distance classes on the scale of populations, but on the scale of individuals, no spatial structure was found in either the whole area of Shandong Province or the area of each sampled county. Although the change of frequencies of the two alleles with geographic locations in Shandong Province both showed gradual increase trends, their changing directions were inverse. The frequency of CCR2-64I allele gradually increased from the southwest to the northeast, while the frequency of SDF1-3'A allele gradually increased from the northeast to the southwest. However the RH to AIDS of combined types of their different genotypes did not represent obvious geographic diversity on the whole area of the Province. CONCLUSION: The frequency of allele usually has some spatial genetic structures or spatial autocorrelation with different spatial distance classes, but the genotypes of individuals have random distribution in the same geographic area. Evaluating spatial distribution of the genetic susceptibility of HIV (AIDS) to CCR2-64I and SDF1-3'A alleles, should focus on the frequencies of combined genotypes of CCR2 and SDF1 based on the two-locus genotypes of each individual rather than the frequencies of CCR2-64I and SDF1-3'A alleles.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Spatial firing properties of hippocampal theta cells.

Previous studies have shown that complex-spike cells, the most common cell type recorded in the hippocampus of freely moving rats, have the property of spatial firing--that is, a cell will fire rapidly only when the animal is in a particular part of its environment (O'Keefe and Dostrovsky, 1971). In the current study, we analyze the spatial firing of theta cells, the second major class of cells in the hippocampus, which are thought to correspond to nonpyramidal neurons (Fox and Ranck, 1975, 1981). Our purposes were to extend findings from earlier spatial analyses (McNaughton et al., 1983; Christian and Deadwyler, 1986), and to determine whether the spatial firing is cell specific and independent of behavior. Theta cells were recorded from rats in a cylindrical enclosure using techniques previously used for the analysis of spatial firing in complex-spike cells (Muller et al., 1987). The spatial firing patterns of individual neurons appeared as a complex surface with several regions of high and low firing. The ratio of firing from high- to low-rate regions averaged 2.5. These spatial firing patterns were smooth and reproducible, but less so than for complex-spike cells. When a cue card on the wall was moved, theta cell firing patterns remained in register with the cue. Two analyses were performed to determine whether spatial firing patterns were secondary to spatial distributions of behavior. When only locomotor data segments were selected, spatial variations were more clear-cut. In an attempt to test whether theta cells had cell-specific patterns of firing, pairs of theta cells were recorded simultaneously. On all occasions, the firing distribution for each of the cells in a pair was clearly distinctive. These findings support the conclusions that theta cell activity contains a spatial signal that is cell specific and not secondary to other firing correlates.

Action Potentials↗