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PubMed2003

Sex differences in spatial and non-spatial Y-maze performance after chronic stress.

Chronic restraint is known to alter hippocampal CA3 dendritic morphology and spatial memory in male rats. The present study examined whether female rats, which exhibit different anatomical adaptations to chronic stress than those of males, would also show spatial memory impairments. Male and female Sprague-Dawley rats were restrained for 6 h/day for 21 days, a time frame previously demonstrated to cause hippocampal CA3 dendritic atrophy. The day after the last restraint session, rats were tested on a Y-maze, a habituation task that can be used to assess spatial memory. Chronic stress impaired Y-maze performance in both sexes without affecting levels of locomotion as measured by total arm entries in the first minute. However, Y-maze performance of stressed females improved in 2-5 min when chronically stressed males continued to show poor Y-maze performance. The enhanced Y-maze performance of chronically stressed females occurred when total arm entries were higher compared to the entries made by males. Therefore, correlations were performed between total arm entries and spatial memory in 1 and 2-5 min. In the first minute when control females demonstrated functional spatial memory, female controls with the lowest locomotor levels exhibited the best performance. The correlations for stressed females were not significant, and neither were the correlations for any group in 2-5 min. Overall, these results show important sex differences in response to chronic stress with females exhibiting an ability to recover quickly from deficits in Y-maze performance.

Animals↗
PubMed2001

A view model which accounts for the spatial fields of hippocampal primate spatial view cells and rat place cells.

Hippocampal spatial view cells found in primates respond to a region of visual space being looked at, relatively independently of where the monkey is located. Rat place cells have responses which depend on where the rat is located. We investigate the hypothesis that in both types of animal, hippocampal cells respond to a combination of visual cues in the correct spatial relation to each other. In rats, which have a wide visual field, such a combination might define a place. In primates, including humans, which have a much smaller visual field and a fovea which is directed towards a part of the environment, the same mechanism might lead to spatial view cells. A computational model in which the neurons become organized by learning to respond to a combination of a small number of visual cues spread within an angle of a 30 degrees receptive field resulted in cells with visual properties like those of primate spatial view cells. The same model, but operating with a receptive field of 270 degrees, produced cells with visual properties like those of rat place cells. Thus a common hippocampal mechanism operating with different visual receptive field sizes could account for some of the visual properties of both place cells in rodents and spatial view cells in primates.

Animals↗
PubMed2003

Preparatory states in crossmodal spatial attention: spatial specificity and possible control mechanisms.

We used event-related functional magnetic resonance imaging to study the neural correlates of endogenous spatial attention for vision and touch. We examined activity associated with attention-directing cues (central auditory pure tones), symbolically instructing subjects to attend to one hemifield or the other prior to upcoming stimuli, for a visual or tactile task. In different sessions, subjects discriminated either visual or tactile stimuli at the covertly attended side, during bilateral visuotactile stimulation. To distinguish cue-related preparatory activity from any modulation of stimulus processing, unpredictably on some trials only the auditory cue was presented. The use of attend-vision and attend-touch blocks revealed whether preparatory attentional effects were modality-specific or multimodal. Unimodal effects of spatial attention were found in somatosensory cortex for attention to touch, and in occipital areas for attention to vision, both contralateral to the attended side. Multimodal spatial effects (i.e. effects of attended side irrespective of task-relevant modality) were detected in contralateral intraparietal sulcus, traditionally considered a multimodal brain region; and also in the middle occipital gyrus, an area traditionally considered purely visual. Critically, all these activations were observed even on cue-only trials, when no visual or tactile stimuli were subsequently presented. Endogenous shifts of spatial attention result in changes of brain activity prior to the presentation of target stimulation (baseline shifts). Here, we show for the first time the separable multimodal and unimodal components of such preparatory activations. Additionally, irrespective of the attended side and modality, attention-directing auditory cues activated a network of superior frontal and parietal association areas that may play a role in voluntary control of spatial attention for both vision and touch.

Attention↗
PubMed1990

Spatial-filter selection in large-scale spatial-interval discrimination.

Spatial-interval discrimination thresholds were measured for a pair of bars in the presence of other parallel bars placed far enough from the targets as to be outside the range of neural and optical blurring. Thresholds were elevated when the targets were embedded in an array of four parallel bars (two between and two flanking the targets), but not when there were only two parallels, whether the parallels were between the target bars or flanking them. The threshold elevation was larger with a 100-msec than with a 500-msec exposure duration. Attenuating the high spatial frequencies magnified the threshold elevation. The data indicate that the process responsible for spatial-interval discrimination automatically selects which spatial filters to use; it does not have to scan through all ranges of spatial filters.

Contrast Sensitivity↗
PubMed1995

A labeled lines explanation of the perceived spatial frequency of moderate-, near-threshold- and zero-contrast spatial patterns.

We tested the predictions of a multiple-channels model about the appearance of spatial patterns. Specifically we tested how encoding the perceived spatial frequency of a near-threshold pattern compared with encoding of a zero-contrast or moderate-contrast pattern. For example, the model predicts that the mean perceived spatial frequency of a near-threshold pattern is a weighted average of the response to the stimulus and the noise. Six subjects used the method of adjustment procedure to match a peripherally viewed test stimulus (or a blank) with a foveally viewed grating. For near-threshold patterns we found a smooth perceived spatial-frequency function, with a smaller range of perceived spatial frequencies than obtained for 0.16 contrast patterns. These results are consistent with the predictions of the model: noise can affect the appearance of near-threshold and zero-contrast patterns.

Contrast Sensitivity↗
PubMed1996

Effect of spatial scale and background luminance on the intensive and spatial nonlinearities in texture segregation.

Perceived segregation between element-arrangement textures is affected both by spatial scale and background luminance. The effects on the spatial nonlinearity are consistent with the proposed structure for complex (second-order) channels. The effects on the intensive nonlinearity are not consistent with an early, local nonlinearity but are consistent with either (i) a relatively early, local, nonlinearity occurring before the spatial frequency channels but after a sensitivity-setting stage, or (ii) inhibitory interaction among channels modeled as a normalization network. Thus the texture intensive nonlinearity comes after sensitivity to spatial frequency and background luminance has been determined. For six of seven observers, the texture intensive nonlinearity was compressive by 10% contrast for both increments and decrements (at high background luminance, large spatial scale.

Adaptation, Ocular↗
PubMed1990

The role of the amygdala and the hippocampus in working memory for spatial and non-spatial information.

Male rats received either electrolytic or sham lesions bilaterally into the amygdala, hippocampus or amygdala plus hippocampus, or were assigned to an unoperated control group. After the postoperative recovery period all lesioned and control animals were tested for the ability to master a spatial delayed non-matching-to-sample (DNMS), a visual DNMS and a visuo-tactile DNMS. Retention of these paradigms was evaluated 24 h after the last respective training session. Bilateral lesions of the amygdala severely disrupted the acquisition and retention of a DNMS paradigm with visual and visuo-tactile cues as discriminative stimuli and had no effect on the acquisition and retention of a spatial DNMS. On the contrary, bilateral lesions of the hippocampus impaired the acquisition and retention of spatial DNMS, but the animals with these lesions showed an acquisition and retention of the visual and visuo-tactile DNMS paradigms significantly better than those of animals with amygdala lesions. Combined lesions of the amygdala and hippocampus severely disrupted the acquisition and retention of the 3 paradigms. The contribution of the amygdala and the hippocampus in the working memory for spatial and non-spatial information is discussed.

Amygdala↗
PubMed1985

The development of spatial and class relations in four young children with right-cerebral-hemisphere damage: evidence for an early spatial constructive deficit.

This study followed the development of four children with right-hemisphere injury on a series of manipulative classification tasks to determine whether and how early brain injury affects the development of spatial and class relations. The children were first tested at about 2 years of age. Their data were compared with previously collected data from 18- to 42-month-old normal children, and with data from four young children with left-hemisphere injury. The results showed the children with right-hemisphere injury do not generate a particular spatial relation (next to) in their spatial groupings with the same frequency as normal or left-hemisphere damaged children, although they do generate in and on relations with normal frequency. An apparent deficit in the development of class relations is shown to be secondary to the spatial deficit, in that it is evident only in tasks that require spatial grouping.

Brain↗
PubMed2002

Lateralization of spatial-memory processes: evidence on spatial span, maze learning, and memory for object locations.

Spatial memory is one of the most important cognitive functions in daily life, enabling us to locate objects in our environment or to learn a route or a path. In the present study, we elaborated on the hypothesis that human spatial memory consists of multiple sub-processes, relying on different brain structures. Therefore, 50 patients with an ischemic stroke and 40 healthy participants underwent tests measuring spatial span and maze learning. By means of a computer paradigm the following aspects of memory for object locations were assessed: (1) object location binding; (2) positional memory; (3) a combination of these two aspects. The results clearly showed a double dissociation: the group of patients with an infarct in the left hemisphere (LH) was impaired on object location binding, whereas the group with an infarct in the right hemisphere (RH) was impaired on positional memory. Lesions in the RH resulted also in impairments on maze learning. Moreover, patients with lesions in the posterior part of the parietal or the occipital lobe performed especially worse on spatial-memory tasks. These findings extend the theoretical framework of categorical versus coordinate spatial processing in the human brain and corroborate previous findings on selective aspects of memory for object locations.

Adult↗
PubMed1997

The spatial limit for motion detection in noise depends on element size, not on spatial frequency.

When a random spatial noise pattern is displaced for a short distance it seems to move coherently, but when the displacement exceeds a certain value, the direction of motion cannot be clearly perceived. We measured the displacement limit (Dmax) for a two-frame sequence and found that it depended on the size of the elements comprising the random pattern, even when low spatial frequencies were removed from the pattern by spatial band-pass filtering. Dmax depended strongly on contrast for the filtered patterns, but less so for the unaltered patterns. The data support a model for low level motion detection in which the maximum motion displacement that can be detected is determined by the mean separation of pattern elements, following a stage of low-pass spatial filtering, and in which the upper spatial displacement depends upon the pattern statistics, not upon the size of detectors in the visual system.

Filtration↗
PubMed1997

Spatial facilitation predicted with end-stopped spatial filters.

We examined the role of putative end-stopped spatial filters in determining spatial facilitation associated with a line target flanked by square inducers. Results obtained in normal and amblyopic observers were well predicted by end-stopping and other receptive field features of end-stopped spatial filters revealed in a modified Westheimer paradigm. The role of target-inducer collinearity, the effects of inducer polarity, and facilitation associated with non-orientational circular targets, were also studied. Our results suggest that spatial facilitation results from antagonism surrounding spatial filter centers, with end-stopping playing a prominent role.

Adult↗
PubMed2000

Spatial pooling in the second-order spatial structure of cortical complex cells.

We investigate what computational mechanisms give rise to the nonlinearity of complex cell responses in the primary visual cortex. Complex cells are characterized by their nonlinear spatial properties such as spatial phase invariance and nonlinear spatial additivity. We carried out network simulations to estimate the second-order Wiener-like kernels for several different models. Models with nonlinear spatial pooling of simple-cell-like linear subunits reproduce the second-order kernels in good agreement with physiologically estimated kernels, while models without the pooling mechanism fail to reproduce the kernel. The results support the cascade mechanism consisting of simple cells' local feature extraction followed by spatial pooling.

Humans↗
PubMed2002

Effect of visual-spatial ability on learning of spatially-complex surgical skills.

Visual-spatial ability is thought to be important in competency in specific surgical procedures. To test this hypothesis, 37 surgical residents completed six tests of visual-spatial ability, ranging from low-level to high-level visual processing. Using previously validated and objective instruments, we then assessed their ability to complete and learn a spatially-complex surgical procedure. Residents with higher visual-spatial scores in the form-board test and the mental-rotations test did significantly better in the procedure than did those with lower scores. After practice and feedback, residents with lower scores achieved a comparable level of competency. Our results suggest that visual-spatial ability is related to competency and quality of results in complex surgery, and could potentially be used in resident selection, career counselling, and training.

Animals↗
PubMed2003

Spatial and non-spatial learning in turtles: the role of medial cortex.

In mammals and birds, hippocampal processing is crucial for allocentric spatial learning. In these vertebrate groups, lesions to the hippocampal formation produce selective impairments in spatial tasks that require the encoding of relationships among environmental features, but not in tasks that require the approach to a single cue or simple non-spatial discriminations. In reptiles, a great deal of anatomical evidence indicates that the medial cortex (MC) could be homologous to the hippocampus of mammals and birds; however, few studies have examined the functional role of this structure in relation to learning and memory processes. The aim of this work was to study how the MC lesions affect spatial strategies. Results of Experiment 1 showed that the MC lesion impaired the performance in animals pre-operatively trained in a place task, and although these animals were able to learn the same task after surgery, probe test revealed that learning strategies used by MC lesioned turtles were different to that observed in sham animals. Experiment 2 showed that the MC lesion did not impair the retention of the pre-operatively learned task when a single intramaze visual cue identified the goal. These results suggest that the reptilian MC and hippocampus of mammals and birds function in quite similar ways, not only in relation to those spatial functions that are impaired, but also in relation to those learning processes that are not affected.

Animals↗
PubMed1992

A new one-trial test for neurobiological studies of memory in rats. III. Spatial vs. non-spatial working memory.

Rats were submitted to object and spatial recognition tests (both based on the same paradigm) and to the radial-arm maze. The results are as follows: (1) rats could discriminate between a new and a familiar object when the retention delay was 1 min, 15 min or 60 min but not 24 h. The relationship between the level of discrimination and intertrial delays is quadratic with a maximum for 15 min. (2) Exposure to distractive stimuli during the retention delay may impair object recognition. (3) Rats discriminated between a new and a familiar space. (4) There is no correlation between the three tests which argues for a multiple form of working memory, especially a spatial and a non-spatial one. (5) Medial septal lesion did not impair object and spatial recognition memory, but the level of discrimination in the spatial recognition test was significantly reduced compared to that of control.

Aging↗
PubMed1997

Ibotenic lesions of the nucleus accumbens promote reactivity to spatial novelty in nonreactive DBA mice: implications for neural mechanisms subserving spatial information encoding.

The role of the nucleus accumbens (NA) in forming spatial representations was investigated in C57BL/6 (C57) and DBA/2 (DBA) inbred mice. One week before testing, bilateral excitotoxic lesions were performed in the NA using ibotenic acid. Testing consisted of placing mice in an arena containing 5 objects at a fixed location and, after habituation to the object configuration, examining their reactivity to the displacement (spatial novelty) or the substitution (object novelty) of some of these objects. C57 mice reacted to spatial novelty and DBA mice did not. Both strains, however, reacted to object novelty. The lesion had no effect on C57 mice's performance, but in the DBA mice, it promoted a clear reaction to spatial novelty that was absent in control animals. Radial maze performance also was improved in DBA with NA lesions. Results suggest the NA as a possible site for modulating spatially mediated behaviors in poor-performing subjects.

Animals↗
PubMed1988

The relationship of undershooting (anticipation) error in space localization to spatial dimension and spatial category width.

In this study I explored whether the degree of anticipation/habituation (undershooting/overshooting) varies with the dimension to be localized, when the method of adjustment is used in space localization. In this study, undershooting occurred for both the vertical (Group 1) and the horizontal (Group 2) dimensions, but was significant only for verticality. The magnitude of undershooting observed for verticality was significantly greater than that for horizontality. A secondary issue regarding the possible relationship between spatial category width and undershooting/overshooting was examined. It was hypothesized that greater degree of spatial category width would be associated with greater undershooting. The opposite was found: Spatial category width was negatively related to undershooting. Finally, within each group, very high consistency of magnitude of spatial category width was observed (rs greater than .90), despite the fact that spatial category width showed shrinkage over the course of the study.

Cognition↗
PubMed1997

Interference in immediate spatial memory: shifts of spatial attention or central-executive involvement?

Interference in serial spatial memory was investigated in six experiments. Experiment 1 replicated Experiment 2 by Smyth and Scholey (1994) in showing that listening to tones that originated from different directions interfered with spatial memory. Experiment 2 showed, however, that the effect of mere listening was not observed when this was the only interference condition experienced by the subject. In Experiment 3, a binary pitch discrimination task performed on spatially separated tones impaired recall performance to the same extent as did left-right decisions. The same disrupting effect was also observed when the tones were presented from the same direction in the pitch discrimination task (Experiment 4) as well as in a binary loudness discrimination task (Experiment 5). Finally, repeating heard words did not interfere, whereas pitch discrimination performed on these same words disrupted recall (Experiment 6). It is argued that the disrupting effects reflect not a specifically spatial interference, but a central executive involvement in the rehearsal process in serial spatial memory.

Attention↗