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At least 271 records · Page 15Linked to original sources
PubMed2005

Physical limits to spatial resolution of optical recording: clarifying the spatial structure of cortical hypercolumns.

Neurons in macaque primary visual cortex are spatially arranged by their global topographic position and in at least three overlapping local modular systems: ocular dominance columns, orientation pinwheels, and cytochrome oxidase (CO) blobs. Individual neurons in the blobs are not tuned to orientation, and populations of neurons in the pinwheel center regions show weak orientation tuning, suggesting a close relation between pinwheel centers and CO blobs. However, this hypothesis has been challenged by a series of optical recording experiments. In this report, we show that the statistical error associated with photon scatter and absorption in brain tissue combined with the blurring introduced by the optics of the imaging system has typically been in the range of 250 microm. These physical limitations cause a systematic error in the location of pinwheel centers because of the vectorial nature of these patterns, such that the apparent location of a pinwheel center measured by optical recording is never (on average) in the correct in vivo location. The systematic positional offset is approximately 116 microm, which is large enough to account for the claimed misalignment of CO blobs and pinwheel centers. Thus, optical recording, as it has been used to date, has insufficient spatial resolution to accurately locate pinwheel centers. The earlier hypothesis that CO blobs and pinwheel centers are coterminous remains the only hypothesis currently supported by reliable observation.

Animals↗
PubMed1996

Dorsal striatal lesions in rats. 2: Effects on spatial and non-spatial learning.

Rats with small electrolytic lesions of the dorsal striatum were evaluated in acquisition of spatial learning, sensorimotor learning, and a straight runway food approach response and its extinction. No differences were detected between rats with dorsal striatal lesions and sham-operated controls during acquisition of hidden and visible trials in the Morris water maze. Neither was an intergroup difference observed during acquisition of the rotorod test of motor coordination. Lesioned rats were not impaired in running for a food reward, but their running latencies on day 2 of extinction were lower than those of controls, an indication of perseveration. These results indicate that perseverative responding may occur in dorsal striatal lesioned rats in the absence of spatial or sensorimotor defects.

Analysis of Variance↗
PubMed2003

Recovery of spatial memory and persistence of spatial orientation deficits after traumatic brain injury during childhood.

The present study set out to examine the recovery of spatial learning and cognitive mapping skills after severe TBI in childhood. A prospective investigation was carried out with repeated measures. Children with TBI (n = 18) and healthy matched controls (n = 18) were investigated while the children with TBI stayed in a rehabilitation facility (t0) and 4 years later (t1). Children were assessed with the Kiel Locomotor Maze, where they had to remember defined locations in an experimental chamber with completely controlled intra- and extra-maze cues until the learning criterion was reached. During probe trials, cognitive mapping strategies were assessed. Results showed (i) that spatial learning is functionally restituted 4 years post-trauma and (ii) that cognitive mapping skills are still impaired 4 years post-trauma. It was concluded that cognitive performance of children who survived a severe TBI may he overestimated, having far reaching consequences for the children.

Analysis of Variance↗
PubMed2006

Parameter-based assessment of spatial and non-spatial attentional deficits in Huntington's disease.

A major challenge for neuropsychological research on Huntington's disease is the identification of biomarkers for the disease at the level of cognitive functions. Given that cortical-striatal-thalamic circuits are particularly vulnerable, possible markers loading functionally on these brain regions should be particularly significant. We investigated whether parametric values derived from a 'theory of visual attention' (TVA) can serve that purpose. They are derived as mathematically independent, quantitative measures of attentional components, and the tasks require only non-speeded vocal responses. As such, the methodology seems well suited for testing patients with motor problems and general cognitive decline. Accumulating neuroanatomical evidence suggests that striatal atrophy in Huntington's disease is asymmetrical with a more pronounced left-sided degeneration. We applied a partial-report paradigm to analyse whether this results in a pathological (leftward) bias of the spatial distribution of attention. In partial report, red target letters are presented either alone or accompanied by either a second target or a green distractor letter presented in the same or in the opposite hemi-field. Since basal ganglia lesions have also been shown to cause spatially non-lateralized impairments, that is, reduced perceptual processing speed and visual working memory (WM) storage capacity within both hemi-fields, we tested possible reductions in these parameters with a whole-report paradigm. Here, columns of five red or green letters are briefly presented and the subject has to report as many as possible. Eighteen patients and 18 matched control subjects performed a partial- and a whole-report task with briefly presented letter displays. In partial report, Huntington's disease patients demonstrated a pathological bias, indicating increased attentional weighting to the left hemi-field. The extent of lateralization was strongly related to age at onset and to the number of cytosine-adenine-guanine (CAG) triplet repeats on gene IT15. In contrast, the extent of lateralization was not related to disease progression as reflected by the duration of the disease since onset of the first symptoms. In whole report, the non-lateralized attentional parameters processing speed and visual WM storage capacity were reduced bilaterally in both hemi-fields. The extent of the reduction was related to the disease duration since onset, whereas no significant correlation with CAG repeats or age at onset was found. Laterality of attentional weighting may, therefore, represent a possible trait marker reflecting the intensity of the pathogenic mechanisms, while the reduction of visual processing speed and storage capacity may be state markers for the stage of disease progression.

Adult↗
PubMedDate not supplied

Prefrontal cortex and working memory for spatial response, spatial location, and visual object information in the rat.

In the first experiment, rats were trained on a working memory task for a spatial response (right-left turn) information using a delayed matching-to-sample procedure. Following lesions of the medial prefrontal cortex (MPF), which includes anterior cingulate and medial precentral cortex, there was a profound working memory deficit even at the shortest delay. In the second experiment, rats were trained on a working memory task for spatial location information using a delayed matching-to-sample procedure. Following lesions of the MPF, there was only a mild working memory deficit, whereas following dorsal hippocampal lesions there was a profound working memory deficit even at the shortest delay. In the third experiment, rats were trained on a working memory task for visual object information using a delayed nonmatching-to-sample procedure. Following lesions of the MPF, there were no working memory deficits, whereas following lesions of the prelimbic and infralimbic cortex there was a profound working memory deficit even at the shortest delay. The results suggest that different neural subregions of the prefrontal cortex mediate working memory for specific attribute information.

Animals↗
PubMed1978

Spatial errors made by infants: inadequate spatial cues or evidence of egocentrism?

Nine month old infants search correctly for an object which they have seen hidden in one position, but cease to do so after they have been moved to the opposite side of the display, searching instead at a position which is apparently defined egocentrically from their experience before movement. This error can be explained on the one hand in terms of response dependence or egocentrism, or on the other hand as due to a lack of adequate spatial cues to allocentric position. In order to distinguish between these hypotheses, 64 nine month old infants were presented with a hidden object problem in which the two alternative positions had covers of different colours. The results show that infants could search correctly for an object in one location although they saw the problem from different sides. This result combines with those of other conditions to indicate that cover colour provides an adequate spatial cue, allowing the infant to specify position allocentrically, provided the correct cover maintains a stable position.

Child Development↗
PubMed2001

Bioacoustic spatial perception by humans: a controlled laboratory measurement of spatial resolution without distal cues.

The angular spatial resolution of a wide-angle air sonar using a continuous transmission frequency-modulated radiation, with the output coupled binaurally to the auditory system of a user, was measured under restrained controlled conditions. This was done to determine the effect of adding a narrow central field of view of 9 deg to a wide-angle sonar. The target objects were three equidistant vertical rods initially spaced apart by 10 deg. This was varied down to a spacing of 4 deg. Ten nonvisual subjects achieved an angular resolution of 6 deg. Four of these ten subjects continued learning to achieve an unexpected spatial resolution of 4 deg within the 9 deg central field. A mean error of approximately 1 deg in direction accuracy was achieved. It is inferred that the unique variations in the octave band ultrasonic echoes within the narrow field, and the invariance of the on-axis echo as one's head is turned, enables this angular resolution and accuracy to be achieved within the wide binaural field of view of 50 deg. This ability to resolve specula objects within a narrow angular resolution element of 9 deg is linked to the bat's ability to seemingly resolve object glints within a distal resolution element of less than 2 wavelengths.

Acoustic Stimulation↗
PubMed2003

Spatial characterization of laser-induced plasmas by deconvolution of spatially resolved spectra.

The spatial characterization of laser-induced plasmas, including their temperature, electron density, and relative atom density, has been carried out by emission spectroscopy. The plasmas were generated with iron samples in air and argon at atmospheric pressure. An imaging spectrometer equipped with an intensified CCD detector procured spectra with spatial resolution. The plasma characterization was made at three temporal gates (2-3, 5-6, and 9-11 micros) to permit the plasma's evolution to be studied. A deconvolution procedure was developed to transform the measured intensity, integrated along the line of sight, into the radial distribution of emissivity. Temperature and electron density distributions were obtained under the assumption of local thermodynamic equilibrium and Stark broadening of the emission lines. The relative atom density distributions in the plasma of the Fe atoms arising from the sample and of the Ar atoms arising from the ambient gas were determined and evidenced an important interaction between the plasma and the surrounding atmosphere.

Journal Article↗
PubMed2004

Phase calibration of spatially nonuniform spatial light modulators.

A new 512 x 512 pixel phase-only spatial light modulator (SLM) has been found to deviate from being flat by several wavelengths. Also, the retardation of the SLM relative to voltage varies across the device by as much as 0.25 wavelength. The birefringence of each pixel as a function of address voltage is measured from the intensity of the SLM between crossed polarizers. To these responses are added a reference spatial phase measured by phase shifting interferometry for a single address voltage. Fits to the measured data facilitate the compensation of the SLM to a root-mean-square wave-front error of 0.06 wavelength. The application of these corrections to flatten the full aperture of the SLM sharpens the focal plane spot and reduces the distortion of computer-designed diffraction patterns.

Journal Article↗
PubMed2000

Population dynamics of Pseudomonas sp. along a spatial gradient of phosphate: an experimental approach for spatial ecology.

Many theoretical models have been proposed to study the effect of space on population dynamics and interactions, but most of them are difficult to translate into experimental setups due to their abstract nature. Here we defend the gradostat as a valuable experimental tool for testing such theories. The gradostat is a culture system with bi-directional flow that forms nutrient gradients at steady state. In this study, we use a 3-vessel gradostat with a phosphate gradient to study the effect of spatial heterogeneity on the spatial distribution of Pseudomonas sp., an heterotrophic aquatic bacterium. The observed distributions partially agree with theoretical predictions, obtained from a mathematical model.

Ecology↗
PubMed1989

Contrast and spatial variables in texture segregation: testing a simple spatial-frequency channels model.

Observers were shown patterns composed of two textures in which each texture contained two types of elements. The elements were arranged in a striped pattern in the top and bottom regions and in a checked pattern in the center region. Observers rated the degree to which the three regions were seen as distinct. When the elements were squares or lines, perceived segregation resulting from differences in element size could be canceled by differences in element contrast. Minimal perceived segregation occurred when the products of the area and the contrast (areal contrasts) of the elements were equal. This dependence of perceived segregation on the areal contrasts of the elements is consistent with a simple model based on the hypothesis that the perceived segregation of the regions is a function of their differential stimulation of spatial-frequency channels. Two aspects of the data were not consistent with quantitative predictions of the model. First, as the size difference between the large and small elements increased, the ratings at the point of minimum perceived segregation increased. Second, some effects of changing the fundamental frequency of the textures were not predicted by the model. These discrepancies may be explained by a more complex model in which a rectification or similar nonlinearity occurs between two stages of orientation- and spatial-frequency-selective linear filters.

Adult↗
PubMedDate not supplied

[A comparison of the spatial connections of superslow phasic electrical processes recorded from the surface of the head in healthy subjects to the spatial connections of a simultaneously recorded EEG].

The EEG and infraslow phasic electrical processes in the band of 0.05-0.5 Hz (ISPP) were simultaneously recorded in 16 derivations (10-20 System without Fz, Cz, and Pz) in 35 women volunteers in the state of quiet wakefulness with closed eyes. Artifacts and non-stationary segments with a sharp amplitude increase were eliminated from the records in preprocessing editing. Spatial correlations were evaluated using maxima of crosscorrelation functions and coherence functions averaged over the whole spectrum. Correlations for both kind of processes appeared to be rather similar, in particular, they were both characterized by the low values if interhemispheric covariations in the temporal areas. The ISSP correlations were significantly lower for the least distance between derivations and had lower spatial gradient than the EEG correlations. There were also some topical differences between the processes. The obtained evidence support the idea of the ISPP as direct manifestations of cortical electrical activity, however, rather specific in relation with the routine EEG correlations.

Adolescent↗
PubMed2000

Conditionally immortal neuroepithelial stem cell grafts restore spatial learning in rats with lesions at the source of cholinergic forebrain projections cholinergic forebrain projections Conditionally immortal neuroepithelial stem cell grafts restore spatial leaming in rats with lesions at the source of cholinergic forebrain projections.

Purpose: Loss of cholinergic projections from the basal forebrain (BF) to the cortex and from the medial septal area (MSA) to tbe hippocampus is a reliable correlate of cognitive deficits in aging and Alzheimer's disease (AD). We assessed the capacity of grafts of the conditionally immortal MHP36 clonal stem cell line to improve spatial learning in rats showing profound deficits after lesions to these projections. Methods: Rats were lesioned by infusions of S-AMPA unilaterally into BF or bilaterally into both BF and MSA. MHP36 cells were implanted ipsilaterally in cortex or basal forebrain two weeks after unilateral BF lesions, and in cortex and hippocampus bilaterally six months after bilateral BF-MSA lesions. Intact and lesion-only controls received vehicle. Six weeks later rats were assessed in spatial learning and memory tasks in the water maze, and then perfused for identification of grafted cells by beta-galactosidase immunohistocheniistry. Results: Lesioned rats with MHP36 grafts, whether implanted two weeks or six months after lesioning, learned to find a submerged platform in the water maze as rapidly as intact controls, and showed a strong preference for the platform quadrant on probe trials, whereas lesioned controls were impaired in all measures. Grafted cells of both neuronal and glial morphologies, migrated away from cortical implantation sites in BF Lesioned rats to the striatum, thalamus and basal forebrain lesion area. Cells implanted in basal forebrain showed a similar distribution. In rats with bilateral BF-MSA lesions, grafts implanted in the hippocampus migrated widely through all layers but cortical grafts largely escaped up the needle tract into the meninges. Conclusions: Although MHP36 grafts were functionally effective in both lesion models, the site and age of lesions and site of implantation influenced the pattern of engraftment. This flexibility encourages the development of conditionally immortal human stem cell lines with similar capacities for functional repair of variable neuronal degeneration in AD or aging.

Journal Article↗
PubMed2002

The coding of spatial location by single units in the lateral superior olive of the cat. I. Spatial receptive fields in azimuth.

The lateral superior olive (LSO) is one of the most peripheral auditory nuclei receiving inputs from both ears, and LSO neurons are sensitive to interaural level differences (ILDs), one of the primary acoustical cues for sound location. We used the virtual space (VS) technique to present over earphones broadband stimuli containing natural combinations of localization cues as a function of azimuth while recording extracellular responses from single LSO cells. The responses of LSO cells exhibited spatial receptive fields (SRFs) in azimuth consonant with their sensitivity to ILDs of stimuli presented dichotically: high discharge rates for ipsilateral azimuths where stimulus amplitude to the excitatory ear exceeded that to the inhibitory ear, rapidly declining rates near the midline, and low rates for contralateral azimuths where the amplitude to the inhibitory ear exceeded that to the excitatory ear. Relative to binaural stimulation, presentations of the VS stimuli to the ipsilateral ear alone yielded increased rates, particularly in the contralateral field, confirming that the binaural SRFs were shaped by contralateral inhibition. Our finding that LSO neurons respond to azimuth consistent with their ILD sensitivity supports the long-held hypothesis that LSO neurons compute a correlate of the ILD present in free-field stimuli. Only weak correlations between the properties of pure-tone ILD functions and the SRFs were found, indicating that ILD sensitivity measured at only one sound level is not sufficient to predict sensitivity to azimuth. Sensitivity to spatial location was also retained over a wide range of stimulus levels under binaural, but not monaural, conditions.

Acoustic Stimulation↗
PubMed2002

The coding of spatial location by single units in the lateral superior olive of the cat. II. The determinants of spatial receptive fields in azimuth.

The lateral superior olive (LSO) is one of the most peripheral nuclei in the auditory pathway to receive inputs from both ears, and its cells are sensitive to interaural level disparities (ILDs) when stimulated by sounds presented over earphones. It has, accordingly, long been hypothesized that the functional role of the LSO is to encode a correlate of ILDs, one of the acoustical cues to the spatial location of sound. In the companion paper, we used the virtual space (VS) technique to present over earphones stimuli containing all the acoustical cues to the location of broadband stimuli and measured the spatial receptive fields (SRFs) in azimuth of single LSO cells. The shapes of the SRFs were generally consistent with the ILD sensitivity of the cells (Tollin and Yin, 2002), but because the only variable under our control was azimuth, and not ILD directly, the precise cues responsible for the SRFs could not be unambiguously determined. Here, we test more directly the hypothesis that ILDs are the primary determinants of the SRFs in azimuth of LSO cells by digitally manipulating the head-related transfer functions used to create the VS stimuli by independently varying (or holding constant) in azimuth each of the primary localization cues in isolation while holding constant (or varying) the others. Our results support the classical view of the LSO that the form of the SRFs of the cells in azimuth is determined primarily by the ILDs in a small band of frequencies around the characteristic frequencies of the cells.

Acoustic Stimulation↗
PubMed1975

[A way to spatial irradiation planning. II. Vectorial demonstration of spatial dose distribution within a single-ray beam and 1st consequences for the practice].

Spatial irradiation planning among other things demands spatial consideration of the dose distribution within the single useful ray beam. From this point of view, the vectorial dose quantities introduced in part I of this paper are reviewed, their correlations are examined as well as their dependences on different influencing quantities e.g. on the rotational position of the wedge filter with the central ray as an axis of rotation. The vectorial description of dose distribution used in this paper, additionally offers information on the total effect upon the inclination of isodose surfaces or curves respectively, caused either simultaneously by different influences (simultaneous effect) or in temporal succession by separate influences (succession effect). The correlations observed can be verified diagrammatically or dosimetrically using simple practical examples. Thus, it is possible for instance to obtain a continuous defined variation of the isodose inclination by varying the weights of the partial doses with successive irradiation with or without a wedge filter.

Humans↗
PubMed1988

Unilateral spatial neglect: biases in contralateral search and fine spatial attention.

Contralateral search and fine spatial attentional asymmetries, two aspects of hemispatial neglect, were examined in a total of 91 right brain damaged (RBD) and 40 non-aphasic left brain damaged (LBD) stroke rehabilitation inpatients. Fine spatial attentional asymmetries within a hemispace were found in both RBD and LBD patients on the LAVA figure-match test. This finding is in contrast to Gainotti's hypothesis that such problems in extracting contralateral visual information are uniquely characteristic of RBD patients. Furthermore, the study suggests that the gross search and fine attentional aspects of neglect are dissociable and may reflect different underlying mechanisms of hemispatial neglect.

Journal Article↗
PubMed1983

[Relation between the spatial and spatial-frequency characteristics of receptive fields of the cat visual cortex].

Spatial (the size and the eccentricity) and spatial-frequency (optimal frequency and the bandwidth) characteristics of receptive fields of the cat visual cortex were studied. The linear and quasilinear receptive fields of equal size were shown, in accordance with predictions of the piecewise Fourier analysis, to constitute a module in every field of which the complexity index (ratio of the field size vs. the number of its optimal frequency periods) equaled the optimal frequency multiplied by a coefficient constant for a given module. Five modules were found with field sizes 2.6 degrees; 3.8 degrees; 5.2 degrees; 6.2 degrees and 7.0 degrees moving toward the visual field periphery as the modules increased in size. According to the predictions, the bandwidth decreases in the reversed proportion to the field size in a fixed complexity index. The data obtained corroborate the hypothesis implying that the receptive fields perform a piece wise quasi--Fourier expansion of an image.

Animals↗