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Human hippocampus and viewpoint dependence in spatial memory.

Virtual reality was used to sequentially present objects within a town square and to test recognition of object locations from the same viewpoint as presentation, or from a shifted viewpoint. A developmental amnesic case with focal bilateral hippocampal pathology showed a massive additional impairment when tested from the shifted viewpoint compared with a mild, list length-dependent, impairment when tested from the same viewpoint. While the same-view condition could be solved by visual pattern matching, the shifted-view condition requires a viewpoint independent representation or an equivalent mechanism for translating or rotating viewpoints in memory. The latter mechanism was indicated by control subjects' response latencies in the shifted-view condition, although the amnesic case is not impaired in tests of mental rotation of single objects. These results show that the human hippocampus supports viewpoint independence in spatial memory, and suggest that it does so by providing a mechanism for viewpoint manipulation in memory. In addition, they suggest an extremely sensitive test for human hippocampal damage, and hint at the nature of the hippocampal role in episodic recollection.

Adult↗

The role of attention in a spatial memory task in Alzheimer disease patients.

Memory and attention are interrelated cognitive processes that most likely influence the functioning of each other, yet they are often difficult to distinguish in psychological experiments. Young, aged adults, and patients with Alzheimer disease (AD) were tested on a delay response task measuring spatial memory that also placed high demands on attentional resources. Aged adults performed as well as young, suggesting that neither attentional nor memory abilities were exceeded in either group. However, AD subjects were severely impaired on this task. Two further experiments with AD patients examined the relative contribution of attentional and memory deficits in the performance of this population. Both memory and attentional impairments were found; however, errors due to memory factors were more closely related to severity of disease as measured on the Folstein Mini-Mental State Examination than were errors of attentional origin. These studies demonstrate the necessity of accounting for attentional components in studies examining memory, especially in patients with AD.

Adult↗

Spatial memory of body linear displacement: what is being stored?

The ability to evaluate traveled distance is common to most animal species. Head trajectory in space is measured on the basis of the converging signals of the visual, vestibular, and somatosensory systems, together with efferent copies of motor commands. Recent evidence from human studies has shown that head trajectory in space can be stored in spatial memory. A fundamental question, however, remains unanswered: How is movement stored? In this study, humans who were asked to reproduce passive linear whole-body displacement distances while blindfolded were also able to reproduce velocity profiles. This finding suggests that a spatiotemporal dynamic pattern of motion is stored and can be retrieved with the use of vestibular and somesthetic cues.

Acceleration↗

Excitotoxic lesions centered on perirhinal cortex produce delay-dependent deficits in a test of spatial memory.

Rats with bilateral electrolytic or ibotenic acid lesions that were centred in perirhinal cortex displayed a significant delay-dependent deficit on a delayed nonmatch to position task in the T maze. Although the removal of prominent extramaze visual cues did not affect the performance of these rats, rotating the maze between the sample and test phases did, indicating that rats were using a spatial strategy. Interestingly, a further group of rats with hippocampal and perirhinal damage displayed deficits that may reflect a dysfunction in the use of inertial cues. These results suggest that both electrolytic and excitotoxic lesions of perirhinal cortex produce spatial memory impairments but that these impairments are qualitatively different than those exhibited following hippocampal damage.

Analysis of Variance↗

Spatial memory in the desert kangaroo rat (Dipodomys deserti).

Desert kangaroo rats (Dipodomys deserti) forage for seed distributed in patches in the desert environment and may remember patch locations. In Experiment 1, 7 desert kangaroo rats that had discovered the location of a plastic token in 1 box accurately dug for a token hidden in the same location in a 2nd identical box. Results of Experiment 2 indicated that the rats primarily remembered the spatial location of the token within the box in relation to extramaze objects and the walls of the experimental box. Female rats also remembered the chip's location in relation to objects inside the box, but males did not. Experiment 3 demonstrated that the rats' ability to locate the buried token did not depend on detection of the odor of the token. In the discussion I propose that spatial memory in kangaroo rats may have evolved as a result of an overall change in the ontogeny of the species rather than as a specialized adaptation for foraging efficiency.

Animals↗

Effects of vasopressin on histamine H(1) receptor antagonist-induced spatial memory deficits in rats.

The effects of [Arg(8)] vasopressin on histamine H(1) receptor antagonist-induced memory deficits were investigated using the eight-arm radial maze performance test in rats. Pyrilamine and diphenhydramine as well as scopolamine induced memory deficits characterized by increases in the number of total errors, reference memory errors and working memory errors. [Arg(8)] vasopressin improved not only scopolamine--but also pyrilamine--and diphenhydramine-induced memory deficits, although a high dose of [Arg(8)] vasopressin was needed to antagonize pyrilamine-induced memory deficits. The effects of pyrilamine on the brain [Arg(8)] vasopressin content were studied, and the hippocampus [Arg(8)] vasopressin content was shown to be decreased after pyrilamine injection. From these observations, it seems likely that [Arg(8)] vasopressin participates in not only the cholinergic system but also the histaminergic system in spatial memory.

Animals↗

Spontaneous recovery of deficits in spatial memory and cholinergic potentiation of NMDA in CA1 neurons during chronic lithium treatment.

The therapeutic action of lithium in affective disorders is still unclear. One effect of lithium is to deplete membrane inositol and consequently to exhaust the phosphoinositide (PI) pathway. Under chronic lithium treatment, rats showed persistent performance deficits in an active avoidance task and in a visually cued maze. The same treatment, however, resulted in only a transient deficit in the performance of rats in a spatial memory task. Lithium treatment caused a similarly transient deficit in the ability of acetylcholine to potentiate responses to N-methyl-D-aspartate (NMDA) in neurons of the hippocampal slice. The authors propose that the development of compensatory mechanisms may account for the lack of severe memory impairments during lithium treatment. It is suggested that the effects of lithium on the PI pathway are not sufficient to explain the behavioral consequences of chronic lithium treatment.

Acetylcholine↗

Ca2+-independent phospholipase A2 inhibitor impairs spatial memory of mice.

Pharmacological blockade of Ca2+-independent phospholipase A2 (PLA2) is reported to disintegrate hippocampal synaptic plasticity, which is thought to be the cellular mechanism underlying learning and memory. Therefore, we investigated the effect of the Ca2+-independent PLA2 inhibitor bromoenol lactone (BEL) on spontaneous alteration behaviors of mice. When 3 nmol BEL was intracerebroventricularly injected 30 min prior to the test, the mice showed a poor alternation ratio, compared with control animals. The data suggest that Ca2+-independent PLA2 activity is required for spatial memory.

Animals↗

Pre- and postnatal choline supplementation produces long-term facilitation of spatial memory.

Although research has demonstrated that short-term improvement in memory function of adult rats can occur when the availability of precursors for the neurotransmitter acetylcholine is increased, little is known about whether memory function of adult rats can be permanently altered by precursor supplementation during early development. In the present study, male albino rats were exposed to choline chloride supplementation both prenatally (through the diet of pregnant rats) and postnatally (subcutaneous injections). At 60 days of age rats were tested on a 12- and 18-arm radial maze task. Results indicated that compared to control littermates, perinatal choline-treated rats showed more accurate performance on both working and reference memory components of the task. This performance difference was apparent on the first block of sessions and continued throughout training. Further analysis revealed that the difference between choline and control rats is not due to use of differential response or cue-use strategies. Instead, it appears that choline induced performance differences are due to long-term enhancement of spatial memory capacity and precision.

Animals↗

Finding your way in the dark: the retrosplenial cortex contributes to spatial memory and navigation without visual cues.

Path integration is presumed to rely on self-motion cues to identify locations in space and is subject to cumulative error. The authors tested the hypothesis that rats use memory to reduce such errors and that the retrosplenial cortex contributes to this process. Rats were trained for 1 week to hoard food in an arena after beginning a trial from a fixed starting location; probe trials were then conducted in which they began a trial from a novel place in light or darkness. After control injections, rats searched around the training location, showing normal spatial memory. Inactivation of the retrosplenial cortex disrupted this search preference. To assess accuracy during navigation, rats were then trained to perform multiple trials daily, with a fixed or a different starting location in light or darkness. Retrosplenial cortex inactivation impaired accuracy in darkness. The retrosplenial cortex may provide mnemonic information, which decreases errors when navigating in the dark.

Animals↗

Amygdala kindling increased fear-response, but did not impair spatial memory in rats.

The behavioral effects of amygdala kindling, a model of experimental epilepsy in rats, are reported. The animals were stimulated twice a day until stage 5 (generalized clonic) seizures were obtained three times. Two weeks later the performance of the amygdala-kindled and sham-operated rats was tested in the open-field test, on the elevated plus maze, elevated bridges, and in the Morris water maze. The results show that amygdala kindling decreased exploratory and other motor activity in the open-field test, had anxiogenic effects on the elevated plus-maze, decreased boldness on the elevated bridges, but had a negligible affect in the spatial memory task. These results suggest that amygdala kindling affects the normal fear reaction of rats, a response that is known to be mediated through the amygdaloid pathways.

Amygdala↗

Oxytocin improves long-lasting spatial memory during motherhood through MAP kinase cascade.

Oxytocin is an essential hormone for mammalian labor and lactation. Here, we show a new function of oxytocin in causing plastic changes in hippocampal synapses during motherhood. In oxytocin-perfused hippocampal slices, one-train tetanus stimulation induced long-lasting, long-term potentiation (L-LTP) and phosphorylation of cyclic AMP-responsive element binding protein (CREB), and MAP kinase inhibitors blocked these inductions. An increase in CREB phosphorylation and L-LTP induced by one-train tetanus were observed in the multiparous mouse hippocampus without oxytocin application. Furthermore, intracerebroventricular injection of oxytocin in virgin mice improved long-term spatial learning in vivo, whereas an injection of oxytocin antagonist in multiparous mice significantly inhibited the improved spatial memory, L-LTP and CREB phosphorylation. These findings indicate that oxytocin is critically involved in improving hippocampus-dependent learning and memory during motherhood in mice.

Animals↗

Impairment of hippocampal CA1 heterosynaptic transformation and spatial memory by beta-amyloid(25-35).

In Alzheimer's disease, the cholinergic damage (reduced neurotransmission) and cognitive impairment occur long before beta-amyloid (Abeta) plaque formation. It has not been established whether the link between soluble Abeta and cholinergic functions contributes to synaptic dysfunction that underlies the cognitive impairment. Here, we report that Abeta(25-35), an active form of Abeta, inhibited long-term synaptic modification that depends on the associative activation of cholinergic and GABAergic inputs when bilaterally injected intracerebroventricularly (icv; 200 microg/site). The Abeta microinjections did not affect single-pulse-evoked glutamatergic and GABAergic synaptic transmission onto the hippocampal CA1 pyramidal cells, while cholinergic intracellular theta; was dramatically reduced by the Abeta(25-35) injection. Spatial memory of the water maze task was also impaired by the bilateral icv Abeta(25-35) injections, while bilateral microinjections of the same dose of Abeta(35-25) was ineffective in affecting the long-term synaptic modification evoked by associative activation of cholinergic and GABAergic inputs, the cholinergic intracellular theta;, or producing memory impairments. Thus restoring the synaptic plasticity involved in this associative activation of cholinergic and GABAergic inputs may offer an important therapeutic target in the treatment of early Abeta-induced memory decline.

Amyloid beta-Peptides↗

Selective immunolesions of CH4 cholinergic neurons do not disrupt spatial memory in rats.

Adult male Long-Evans rats were subjected to bilateral lesions of the cholinergic neurons in the nucleus basalis magnocellularis (NBM) by injection of 0.2 or 0.4 microg 192-IgG-saporin in 0.4 microl phosphate-buffered saline. Control rats received an equivalent amount of phosphate-buffered saline. Starting 2 weeks after surgery, all rats were tested for locomotor activity in their home cage, beam-walking performance, T-maze alternation rates (working memory), reference and working memory performance in a water-maze task, and memory capabilities in the eight-arm radial maze task using uninterrupted and interrupted (delay of 2 min, 2 h and 6 h after four arms had been visited) testing procedures. Histochemical analysis showed a significant decrease of acetylcholinesterase (AChE)-positive reaction products (30-66%) in various cortical regions at the 0.2-microg dose. At the dose of 0.4 microg, there was an additional, although weak, damage to the hippocampus (17-30%) and the cingulate cortex (34%). The behavioral results showed only minor impairments in spatial memory tasks, and only during initial phases of the tests (reference memory in the water maze, working memory in the radial maze). The behavioral effects of the dramatic cholinergic lesions do not support the idea of a substantial implication of cholinergic projections from the NBM to the cortex in the memory processes assessed in this study, but they remain congruent with an involvement of these projections in attentional functions.

Acetylcholinesterase↗

The effect of steroid sulfatase inhibition on learning and spatial memory.

Steroid sulfatase inhibitors can enhance the concentration of the neurosteroid DHEAS in rat brain. Previous studies have demonstrated that the steroid sulfatase inhibitor (p-O-sulfamoyl)-N-tetradecanoyl tyramine (DU-14) could reverse scopolamine induced amnesia in rats in a passive avoidance memory paradigm. The intent of this study was to determine whether chronic pretreatment with DU-14 could reverse scopolamine amnesia and/or enhance spacial memory in the place, probe and cued versions of the Morris water maze (MWM). Rats were divided into four groups and administered IP for 15 days either DU-14 (30.0 mg/Kg) or corn oil (1.0 ml/Kg) vehicle. On training days animals were administered either scopolamine (1.0 mg/Kg) or saline (1.0 ml/Kg). The groups administered DU-14 displayed a significant enhancement in learning and spacial memory in the place version of the MWM, when compared to respective vehicle-scopolamine and vehicle-saline groups. In the probe version, the DU-14-saline group remained in the target quadrant of the maze significantly longer than any of the other groups indicating enhanced retention. In the cued version of the MWM, treatment with DU-14 did not significantly change escape latency suggesting that the steroid sulfatase inhibitor did not alter motivation or locomotion. These results suggest that the chronic administration of steroid sulfatase inhibitors enhance learning and spatial memory in rats.

Amnesia↗

Retroactive interference effects of surprising reward omission on serial spatial memory.

Reward omission was used to produce retroactive interference in a serial delayed-alternation task. Rats were given forced choices in 3 T mazes presented in succession followed by free choices in which the alternate arm in each maze was rewarded. Nonreward during the delay between forced- and free-choice runs produced a decrement in performance (i.e., retroactive interference) in comparison to reward during the delay. Interference in retention of the first maze in a list occurred when the second maze contained surprising reward or omission (i.e., an outcome contrary to previous training in that maze) in comparison to expected reward or omission. In addition to producing retroactive interference, omission sometimes increased alternation in the maze in which it occurred. These results support a differential rehearsal hypothesis of spatial memory.

Animals↗

Integrin requirement for hippocampal synaptic plasticity and spatial memory.

The establishment of memory requires coordinated signaling between presynaptic and postsynaptic terminals in the CNS. The integrins make up a large family of cell adhesion receptors that are known to mediate bidirectional signaling between cells or between cells and their external environment. We show here that many different integrins, including alpha3 and alpha5, are expressed broadly in the adult mouse brain and are associated with synapses. Mice with genetically reduced expression of alpha3 integrin fail to maintain long-term potentiation (LTP) generated in hippocampal CA1 neurons. Mice with reduced expression of the alpha3 and alpha5 integrins exhibit a defect in paired-pulse facilitation. Mice with reduced expression of alpha3, alpha5, and alpha8 are defective in hippocampal LTP and spatial memory in the water maze but have normal fear conditioning. These results demonstrate that several different integrins are involved in physiological plasticity and provide the first evidence of their requirement for behavioral plasticity in vertebrates.

Animals↗

The effect of hypothermia on the rat's spatial memory in the water tank task.

The effect of hypothermia on the retention of the water tank navigation task has been examined in 21 male hooded rats. After a 3-min swimming test on Day 1 the animals were trained on Days 2 and 3 (2 X 12 trials) to find a small submerged platform 1 cm below the surface of a large pool (120 cm in diameter) of opaque water. On Day 4, the rats were divided into three groups (n = 7) which were cooled to colonic temperatures of 22-24 degrees C (H1), 25-27 degrees C (H2), and 28-31 degrees C (H3), respectively, and given 12 retrieval trials in the water tank. Average escape latencies increased from 6 s in normothermic rats on Day 3 to 33, 19, and 12 s on Day 4 in the H1, H2, and H3 groups, respectively. Under the same testing conditions the performance of groups H1, H2, and H3 improved on Day 5 to 20, 8 and 6 s, respectively. It is concluded that spatial memory retrieval is resistant to mild hypothermia (30 degrees C), but that it is severely impaired at body temperatures below 25 degrees C. Reacquisition of the task is slowed down but not fully prevented in deep hypothermia.

Animals↗