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At least 1,603 records · Page 89Linked to original sources
PubMed1988

The effects of time and distance on accuracy of target-directed locomotion: does an accurate short-term memory for spatial location exist?

The present study was an attempt to replicate the findings of an influential set of experiments by Thomson (1980, 1983) in which he demonstrated a highly accurate but transitory short-term memory for target location during locomotion. No evidence of Thomson's rapidly decaying 8 s short-term memory was found in either of the two experiments presented here. The distance to the target, not the elapsed time, was found to be the major variable affecting the accuracy of walks made without the benefit of visual feedback; as target distance increased so did locomotor error. Increasing the elapsed time to more than 8 s between viewing the target and reaching the vicinity of the target had no effect on the accuracy of walks made with eyes closed. When the elapsed time was greater than 30 s, however, performance began to deteriorate. These results suggest, in sharp contrast to Thomson's experiments, that short-term memory for target location decays rather slowly during locomotion. In this regard, short-term memory in locomotor tasks appears to be little different from the kinds of short-term memory associated with other motor acts.

Journal Article↗
PubMed2004

Pre- and post-training infusion of prazosin into the bed nucleus of the stria terminalis impaired acquisition and retention in a Morris water maze task.

The bed nucleus of the stria terminalis (BNST) is interconnected with the amygdala that is implicated in memory modulation. In view of the innervation of this structure by the hippocampus and brain stem noradrenergic nuclei, this study examined the role of BNST noradrenergic activity in acquisition, formation and expression of spatial memory. Male Wistar rats with indwelling cannulae in the BNST were trained on a spatial navigation task in the Morris water maze. Groups of rats received intra-BNST infusion of vehicle, norepinephrine, prazosin or both drugs shortly before or after each daily training session, or shortly before retention tests. Results showed that pre- or posttraining infusion of 1.0 microg prazosin impaired acquisition and retention, but the treatment had no effect on a cued response task. Posttraining infusion of 1.0 microg norepinephrine enhanced acquisition and retention, and this enhancing effect was blocked by simultaneous infusion of 0.3 microg prazosin. Pretest intra-BNST of prazosin or norepinephrine at a dose of 1.0 microg did not impair expression of the spatial navigation memory. These findings suggest that the BNST noradrengergic function is involved in modulating acquisition and formation of spatial memory that engage the hippocampus.

Adrenergic alpha-Agonists↗
PubMed2000

Identifying cortical inputs to the rat hippocampus that subserve allocentric spatial processes: a simple problem with a complex answer.

A consideration of the cortical projections to the hippocampus provides a number of candidate regions that might provide distal sensory information needed for allocentric processing. Prominent among the input regions are the entorhinal cortex, the perirhinal cortex, the postrhinal cortex, and the retrosplenial cortex. A review of these sites reveals the surprising fact that in spite of their anatomical connections, removal of the perirhinal and postrhinal cortices has little or no effect on spatial tasks and hence does not functionally disconnect the hippocampus. Extensive retrosplenial lesions have only mild effects, and even lesions of the entorhinal cortex only partially mimic the effects of hippocampal lesions upon tests of spatial memory. In contrast, studies using c-fos imaging support the involvement of the entorhinal, postrhinal, and retrosplenial cortices, but not the perirhinal cortex. It is argued that there exist multiple aspects of spatial memory, and this is reflected in the multiple routes by which cortical information can reach the hippocampus. One consequence is that lesions in a single site often have surprisingly mild effects on standard spatial tests.

Afferent Pathways↗
PubMed2003

Human hippocampal and parahippocampal activity during visual associative recognition memory for spatial and nonspatial stimulus configurations.

Evidence from animal studies points to the importance of the parahippocampal region (PHR) [including entorhinal, perirhinal, and parahippocampal (PHC) cortices] for recognition of visual stimuli. Recent findings in animals suggest that PHR may also be involved in visual associative recognition memory for configurations of stimuli. Thus far, however, such involvement has not been demonstrated in humans. In fact, it has been argued that associative recognition in humans is critically dependent on the hippocampal formation (HF). To better understand the division of function between HF and PHR during recognition memory in humans, we measured the activity of both areas in healthy young adults during an associative recognition memory task using functional magnetic resonance imaging. To more precisely characterize the nature of the associations that might be coded by the HF and PHR during recognition, subjects were required to learn and were later tested for associations based on either the spatial arrangements of two stimuli or the identity of two stimuli (a face and a tool). An area in the PHC was found to be more active for recognized old configurations than new configurations in both the spatial and identity conditions. The HF, on the other hand, was more active for recognition of new configurations than old configurations and also more active in the spatial than the identity condition. These data highlight the involvement of PHR in the long-term coding of associative relationships between stimuli and help to clarify the nature of its functional distinction from the HF.

Adult↗
PubMed2002

Win-shift and win-stay learning in the short-beaked echidna (Tachyglossus aculeatus).

Numerous previous investigators have explained species differences in spatial memory performance in terms of differences in foraging ecology. In three experiments we attempted to extend these findings by examining the extent to which the spatial memory performance of echidnas (or "spiny anteaters") can be understood in terms of the spatio-temporal distribution of their prey (ants and termites). This is a species and a foraging situation that have not been examined in this way before. Echidnas were better able to learn to avoid a previously rewarding location (to "win-shift") than to learn to return to a previously rewarding location (to "win-stay"), at short retention intervals, but were unable to learn either of these strategies at retention intervals of 90 min. The short retention interval results support the ecological hypothesis, but the long retention interval results do not.

Animals↗
PubMed2004

Testing the importance of the retrosplenial guidance system: effects of different sized retrosplenial cortex lesions on heading direction and spatial working memory.

The present study: (1) tested the importance of the retrosplenial cortex for learning a specific heading direction and distance and, (2) determined if lesion size could explain apparent inconsistencies in the results of different research groups. Dark agouti rats received either 'complete' cytotoxic retrosplenial cortex lesions or 'standard' lesions, the latter sparing the caudal retrosplenial cortex. Animals were first tested on two versions of a "landmark" task in a water maze. In condition 1 animals could use both heading direction and allocentric position, while in condition 2 only heading direction was effective. In condition 1, animals with complete retrosplenial lesions were impaired by the end of training, their profile of performance being consistent with a failure to use allocentric position information. When the water maze task changed (condition 2) so that allocentric cues became redundant, the animals with complete retrosplenial lesions were able to head in the appropriate direction although they showed longer swim paths. Subsequent testing in the radial-arm maze provided more evidence that retrosplenial lesions can disrupt the use of distal (allocentric) room cues. The impairments seen with retrosplenial lesions were often mild but throughout the study performance of rats with 'complete' lesions was more disrupted than those with 'standard' lesions, who often did not differ from the controls. These findings show that lesion size is a critical factor and may explain why some studies have failed to find comparable deficits after retrosplenial cortex lesions.

Animals↗
PubMed2002

Differential contribution of NMDA receptors in hippocampal subregions to spatial working memory.

N-methyl-D-aspartate (NMDA) receptor-dependent synaptic plasticity in the mammalian hippocampus is essential for learning and memory. Although computational models and anatomical studies have emphasized functional differences among hippocampal subregions, subregional specificity of NMDA receptor function is largely unknown. Here we present evidence that NMDA receptors in CA3 are required in a situation in which spatial representation needs to be reorganized, whereas the NMDA receptors in CA1 and/or the dentate gyrus are more involved in acquiring memory that needs to be retrieved after a delay period exceeding a short-term range. Our data, with data from CA1-specific knockout mice, suggest the possibility of heterogeneous mnemonic function of NMDA receptors in different subregions of the hippocampus.

Animals↗
PubMed2005

Cholinergic parameters and the retrieval of learned and re-learned spatial information: a study using a model of Wernicke-Korsakoff Syndrome.

This is a factorial (2 x 2 x 2) spatial memory and cholinergic parameters study in which the factors are chronic ethanol, thiamine deficiency and naivety in Morris water maze task. Both learning and retention of the spatial version of the water maze were assessed. To assess retrograde retention of spatial information, half of the rats were pre-trained on the maze before the treatment manipulations of pyrithiamine (PT)-induced thiamine deficiency and post-tested after treatment (pre-trained group). The other half of the animals was only trained after treatment to assess anterograde amnesia (post-trained group). Thiamine deficiency, associated to chronic ethanol treatment, had a significant deleterious effect on spatial memory performance of post-trained animals. The biochemical data revealed that chronic ethanol treatment reduced acetylcholinesterase (AChE) activity in the hippocampus while leaving the neocortex unchanged, whereas thiamine deficiency reduced both cortical and hippocampal AChE activity. Regarding basal and stimulated cortical acetylcholine (ACh) release, both chronic ethanol and thiamine deficiency treatments had significant main effects. Significant correlations were found between both cortical and hippocampal AChE activity and behaviour parameters for pre-trained but not for post-trained animals. Also for ACh release, the correlation found was significant only for pre-trained animals. These biochemical parameters were decreased by thiamine deficiency and chronic ethanol treatment, both in pre-trained and post-trained animals. But the correlation with the behavioural parameters was observed only for pre-trained animals, that is, those that were retrained and assessed for retrograde retention.

Acetylcholine↗
PubMed1987

Chlordiazepoxide, an anxiolytic benzodiazepine, impairs place navigation in rats.

There are separate proposals that the hippocampus is involved in 'spatial memory' and in the control of 'anxiety'. Despite a larger number of common effects of anxiolytic drugs and hippocampal lesions, no effect of anxiolytic drugs has yet been reported in those spatial tasks which are particularly sensitive to the effects of hippocampal lesions. The present study addresses this issue. Separate groups of rats were treated, i.p., with 5 mg/kg chlordiazepoxide (an anxiolytic benzodiazepine), 1 mg/kg scopolamine (a muscarinic antagonist which has previously been shown to impair spatial learning) and a saline placebo. They were then trained to find a platform which was hidden in a constant location just under the surface of opaque water in a swimming pool. Separate groups of rats were trained with 4 trials per day and with 1 trial per day. Number of trials per day did not significantly influence the effects of the drugs. Chlordiazepoxide and scopolamine produced similar degrees of impairment in spatial learning to each other--but less impairment than has previously been reported with hippocampal lesions. The effectiveness of the anxiolytic drug chlordiazepoxide in the swimming pool, a specifically spatial task, suggests that the opposing concepts of 'spatial memory' and 'anxiety' which have been used previously to describe hippocampal function may represent different aspects of a unitary concept.

Animals↗
PubMedDate not supplied

Evidence for quantitative domain dominance for verbal and spatial working memory in frontal and parietal cortex.

Neuroimaging studies in humans have shown that different working memory (WM) tasks recruit a common bilateral fronto-parietal cortical network. Animal studies as well as neuroimaging studies in humans have suggested that this network, in particular the prefrontal cortex, is preferentially recruited when material from different domains (e.g. spatial information or verbal/object information) has to be memorized. Early imaging studies have suggested qualitative dissociations in the prefrontal cortex for spatial and object/verbal WM, either in a left-right or a ventral-dorsal dimension. However, results from different studies are inconsistent. Moreover, recent fMRI studies have failed to find evidence for domain dependent dissociations of WM-related activity in prefrontal cortex. Here we present evidence from two independent fMRI studies using physically identical stimuli in a verbal and spatial WM task showing that domain dominance for WM does indeed exist, although only in the form of quantitative differences in activation and not in the form of a dissociation with different prefrontal regions showing mutually exclusive activation in different domains. Our results support a mixed dimension model of domain dominance for WM within the prefrontal cortex, with left ventral prefrontal cortex (PFC) supporting preferentially verbal WM and right dorsal PFC supporting preferentially spatial WM. The concept of domain dominance is discussed in the light of recent theories of prefrontal cortex function.

Adult↗
PubMed2000

Bis(7)-tacrine, a novel acetylcholinesterase inhibitor, reverses AF64A-induced deficits in navigational memory in rats.

The novel dimer bis(7)-tacrine (1,7-N-Heptylene-bis-9,9'-amino-1,2,3, 4-tetrahydroacridine), which exhibits higher potency, selectivity and oral activity on acetylcholinesterase inhibition in vivo than tacrine, was evaluated for its ability to reverse AF64A-induced spatial memory impairment in rats using the Morris water maze. The intracerebroventricular injection of AF64A (3 nmol/side) resulted in a substantial increase in the escape latency to find the platform (F(1,7)=30.2, P<0.01). The observed impairment of spatial memory was paralleled by a 47% decrease in choline acetyltransferase activity in the hippocampus. Oral administration of bis(7)-tacrine (0.22-0.89 micromol/kg) dose-dependently reversed the AF64A-induced latency delay to the level of the saline control group (F(4,28)=7.45, P<0. 05). The present study provides additional evidence of bis(7)-tacrine as an ideal candidate for the palliative treatment of Alzheimer's disease.

Animals↗
PubMed2002

Memory loss in old rats is associated with brain mitochondrial decay and RNA/DNA oxidation: partial reversal by feeding acetyl-L-carnitine and/or R-alpha -lipoic acid.

Accumulation of oxidative damage to mitochondria, protein, and nucleic acid in the brain may lead to neuronal and cognitive dysfunction. The effects on cognitive function, brain mitochondrial structure, and biomarkers of oxidative damage were studied after feeding old rats two mitochondrial metabolites, acetyl-l-carnitine (ALCAR) [0.5% or 0.2% (wt/vol) in drinking water], and/or R-alpha-lipoic acid (LA) [0.2% or 0.1% (wt/wt) in diet]. Spatial memory was assessed by using the Morris water maze; temporal memory was tested by using the peak procedure (a time-discrimination procedure). Dietary supplementation with ALCAR and/or LA improved memory, the combination being the most effective for two different tests of spatial memory (P < 0.05; P < 0.01) and for temporal memory (P < 0.05). Immunohistochemical analysis showed that oxidative damage to nucleic acids (8-hydroxyguanosine and 8-hydroxy-2'-deoxyguanosine) increased with age in the hippocampus, a region important for memory. Oxidative damage to nucleic acids occurred predominantly in RNA. Dietary administration of ALCAR and/or LA significantly reduced the extent of oxidized RNA, the combination being the most effective. Electron microscopic studies in the hippocampus showed that ALCAR and/or LA reversed age-associated mitochondrial structural decay. These results suggest that feeding ALCAR and LA to old rats improves performance on memory tasks by lowering oxidative damage and improving mitochondrial function.

Acetylcarnitine↗
PubMed1994

Modeling neural mechanisms of vertebrate habituation: locus specificity and pattern discrimination.

A critical problem in neurobiology is to explain how the central nervous system coordinates pattern discrimination and locus specificity in learning. This problem is investigated in anuran amphibians who demonstrate both locus specificity and pattern discrimination in visual habituation. A neural mechanism is proposed whereby neural circuitry for pattern discrimination is shared by a spatial memory system. Such learning processes are argued to occur in the medial pallium (MP), the anuran's homolog of mammalian hippocampus. Necessary mapping from the shared network to spatial memory is set up by a mechanism that forms topographical connections, with desired orientation determined by activity gradient in presynaptic and postsynaptic layers. The model of MP is tested on both locus and stimulus specific habituation, which involve short-term as well as long-term synaptic plasticity. Successful modeling yields a set of predictions concerning MP organization and learning properties.

Animals↗
PubMed1997

Multistability of cognitive maps in the hippocampus of old rats.

Hippocampal neurons provide a population code for location. In young rats, environments are reliably 'mapped' by groups of neurons that have firing locations ('place fields') that can be stable for several months. Old animals exhibit deficits in spatial memory, raising the question of whether the quality or stability of their hippocampal 'cognitive maps' is altered. By recording from large groups of neurons, we observed the hippocampal spatial code to be multistable. In young rats, the place field maps were reliable both within and between episodes in a familiar environment. In old rats, place field maps were accurate and stable during an episode, but frequently exhibited complete rearrangements between episodes. In a spatial memory task, both young and old rats exhibited bimodal performance, consistent with map multistability early in training. However, the performance of young rats became almost unimodal with further training, whereas that of old rats remained markedly bimodal. The multistability of the hippocampal map provides an insight into the dynamics of neural coding in high-level cortical structures and their changes during ageing, and may provide an explanation for the frequent failure of place recognition in elderly humans.

Aging↗
PubMed2001

Prenatal morphine exposure differentially alters learning and memory in male and female rats.

The present study tested the hypothesis that exposure to morphine on prenatal days 11-18 impairs performance on tasks requiring learning and memory in adult male and female rats. In Experiment 1, a symmetrical maze was used to measure learning. In Experiment 2, an eight-arm radial maze was used to assess working spatial memory. The results of Experiment 1 demonstrated that prenatal morphine exposure reduces the time needed to complete the trials, but does not affect the accuracy of performance in male rats. In contrast, prenatal drug treatment had no effects on either the time or the accuracy of performance in female rats. In Experiment 2, both male and female morphine-exposed rats needed more time to complete regular trials (no delay) than controls; however, morphine exposure in male rats did not affect performance on tasks requiring memory, measured with delay trials, but hindered it in ovariohysterectomized (OVX) female rats. In OVX females, replacement injections of both estrogen and progesterone restored the impairment of performance on delay trials produced by prenatal morphine exposure. Thus, the present study demonstrates that prenatal morphine exposure differentially alters performance of adult male and female rats on tasks requiring learning and spatial memory.

Animals↗
PubMed2002

Orientation specificity and spatial updating of memories for layouts.

This article examines the degree to which knowledge about the body's orientation affects transformations in spatial memory and whether memories are accessed with a preferred orientation. Participants learned large paths from a single viewpoint and were later asked to make judgments of relative directions from imagined positions on the path. Experiments 1 and 2 contribute to the emerging consensus that memories for large layouts are orientation specific, suggesting that prior findings to the contrary may not have fully accounted for latencies. Experiments 2 and 3 show that knowledge of one's orientation can create a preferred direction in spatial memory that is different from the learned orientation. Results further suggest that spatial updating may not be as automatic as previously thought.

Adult↗
PubMed1995

A preliminary evaluation of the cognitive and motor effects of pediatric HIV infection in Zairian children.

Fourteen asymptomatic HIV-infected Zairian children under 2 years of age displayed social and motor developmental deficits on the Denver Developmental Screening Test when compared with 20 HIV-negative cohorts born to HIV-infected mothers and 16 control children. In a second study, 11 infected children over 2 years of age had sequential motor and visual-spatial memory deficits on the Kaufman Assessment Battery for Children and motor development deficits on the Early Childhood Screening Profiles. HIV infection affects central nervous system structures mediating motor and spatial memory development, even in seemingly asymptomatic children. Furthermore, maternal HIV infection compromises the labor-intensive provision of care in the African milieu and undermines global cognitive development in even uninfected children.

AIDS Dementia Complex↗