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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↗

PubMed2004

Eye patching biases spatial attention after thalamic hemorrhage in a patient without spatial neglect: a case report.

Monocular patching has been advocated as a treatment for spatial neglect. Eye patching, however, is also reported to increase spatial bias. Thus, patching brain injury patients for ocular conditions may also impair their attention. To learn if an eye patch may induce asymmetric attention in a patient without spatial neglect, we tested a woman with diplopia after a left thalamic-intraventricular hemorrhage. She had no spatial neglect on bedside attention tasks. Using a laser pointer, she bisected a blank space at near (279 mm) and far (914 mm) distances under 3 conditions: unpatched and wearing a right or left eye patch. Unpatched, she showed no bias. She erred further leftward with right patching at both distances. Right eye patching appeared to induce neglect of right space when the patient performed this task. With left patching, leftward error tended to increase in near space only. Clinicians prescribing eye patches to patients with brain injury even for purely ocular indications, should evaluate them for spatial neglect once the patch is in place.

Adult↗

PubMed2005

Neural correlates of temporal-order judgments versus those of spatial-location: deactivation of hippocampus may facilitate spatial performance.

The retrieval of temporal-order versus spatial-location information was investigated using fMRI. The primary finding in the hippocampus proper, seen in region of interest analyses, was an increase in BOLD signal intensity for temporal retrieval, and a decrease in signal intensity for spatial retrieval, relative to baseline. The negative BOLD signal change with spatial memory processing, while unexpected, is consistent with the recent fMRI literature indicating decreased BOLD can be associated with neuronal activation, and it is argued that the deactivation observed here may facilitate spatial performance. Spatial-location judgments also yielded a stronger (positive) response in the right midfrontal gyrus, while temporal-order judgments (autobiographic condition only) showed greater activity in the left superior temporal gyrus, suggesting greater working memory demands and greater semantization for each judgment type, respectively. Finally, all conditions activated the left midfrontal gyrus, although autobiographic memories showed additional activity in the medial frontal gyrus.

Adult↗

PubMed2006

Evidence for a double dissociation between spatial-simultaneous and spatial-sequential working memory in visuospatial (nonverbal) learning disabled children.

The paper describes the performance of three children with specific visuospatial working memory (VSWM) impairments (Study 1) and three children with visuospatial (nonverbal) learning disabilities (Study 2) assessed with a battery of working memory (WM) tests and with a number of school achievement tasks. Overall, performance on WM tests provides evidence of a double dissociation between spatial-simultaneous processes, underpinning the memorization item positioning in a spatial configuration, and spatial-sequential processes, which allow memorization of the presentation order. In both groups of children of the two studies, a selective impairment either on spatial-sequential or on spatial-simultaneous working memory tasks was observed. These data support the existence of -simultaneous and -sequential modality-dependent processes in visuospatial working memory and confirm the importance of distinguishing between different subtypes of visuospatial (nonverbal) learning-disabled children.

Child↗

PubMed2004

Medial prefrontal cortex is involved in spatial temporal order memory but not spatial recognition memory in tests relying on spontaneous exploration in rats.

The present study describes two novel tasks relying on spontaneous patterns of exploration in a radial-arm maze that can be used to assess spatial recognition memory and spatial temporal order memory (i.e. memory for the order in which places have been visited) in the rat. In the recognition memory task, rats were permitted to freely explore two arms in the maze on a first trial and one 'familiar' arm and one novelly located arm on a second trial 105 min later. In the temporal order memory task, rats were permitted to explore two arms in the maze on a first trial, two novel arms on a second trial 60 min later, and one 'older familiar' arm and one 'more recent familiar' arm on a third trial 45 min later. Using these tasks, we found that rats direct greater exploration at a novel than a familiar arm location, thus showing long-term spatial recognition memory, and at an older familiar arm than a more recent familiar arm, thus showing long-term spatial temporal order memory. Lidocaine inactivation of the mPFC prior to the final trial in each task disrupted performance on the temporal order but not the recognition memory task, thereby demonstrating a role for the mPFC in the retrieval and/or use of temporal order information but not in spatial memory per se. These findings highlight the specific involvement of the rat mPFC in temporal order memory and have important implications for a broader understanding of mPFC function.

Analysis of Variance↗

PubMed2004

Attentional modulation of the human somatosensory evoked potential in a trial-by-trial spatial cueing and sustained spatial attention task measured with high density 128 channels EEG.

We investigated the modulation of the somatosensory evoked potential (SEP) elicited by mechanical stimuli in a spatial sustained attention and a spatial trial-by-trial cueing design by means of high density electrode array EEG recordings. Subjects were instructed to detect rare tactile target stimuli at the to-be-attended hand while ignoring stimuli at the other hand. Analysis of the SEP revealed a highly complex pattern of results. The P50 component was significantly increased for attended stimuli in the sustained attention as opposed to the trial-by-trial cueing condition. However, no difference in amplitude was found for attended as opposed to unattended stimuli. High density electrode array recordings revealed a centero-frontal N140 component (N140c), which preceded the parietal N140 (N140p) by about 20 ms. The N140c exhibited an attention effect in particular in the trial-by-trial spatial cueing condition. The N140p was significantly enlarged with attention across both experimental conditions, but a closer inspection demonstrated that this was mainly due to the great attention effect in the trial-by-trial spatial cueing condition. The late positive component (190-380 ms after stimulus onset) exhibited a significant attention effect in both experimental conditions. The present experiment provides evidence that the attentional modulation of the SEP is different when tactile as opposed to electrical stimuli were used and when only somatosensory stimuli are presented with no further sensory stimulation in other modalities. Furthermore, transient as opposed to sustained spatial attention affected various components of the SEP in a different way.

Adult↗

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↗