Retention Of Spatial Information Research Articles

Equivalent performance in the water maze by rats with an inborn high or low learning capacity in a shuttle box paradigm

The learning capacity of rats with an inborn high performance (HP) and low performance (LP) in an avoidance shuttle box paradigm, was evaluated in the Morris water maze. Escape latencies evaluated in HP and LP rats indicate that acquisition and retention of spatial information were not different from control animals. When a free swim trial was carried out, all groups showed a significant preference towards the target quadrant. Our results suggest that the altered hippocampal physiology described in HP and LP rats does not influence the performance of a spatial task such as the Morris water maze.

Intention to Remember Spatial Location in Movement: Developmental considerations

Using two experiments, we investigated the influence of age and intention to remember on the retention of spatial information about movement. In the first experiment, 86 subjects-6-year-olds, 10-year-olds, and adults-were asked to recall four positions that were presented on the linear slide. Age groups were randomly divided into intentional (IT) and incidental (IC) learn- ing conditions. IT subjects were instructed to remember the positions, whereas IC groups were not. In the second experiment, 120 subjects-7-year- olds, 11-year-olds, and adults-jogged to five positions on a symmetrical 12- sided area with a perimeter of 48 m. Within each age group, subjects were randomly assigned into four conditions: IT and IC groups that were com- posed of two levels-difficult and easy memory'load. Subjects had to recall where five different exercises were presented. In both experiments, accuracy of performance increased and variability decreased as age increased. Al- though there was no significant IT versus IC effect for accuracy of recall in either experiment, intent to remember reduced the variability of recall. The accuracy of spatial location appeared to be automatically encoded into mem- ory. However, intent to learn was important in reducing the variability of spa- tial response, a characteristic considered quite important to motor skill acquisition.

Learning and memory after adrenalectomy-induced hippocampal dentate granule cell degeneration in the rat.

Adrenalectomy (ADX) of normal adult rats causes selective hippocampal dentate granule cell degeneration that is prevented by corticosterone. The ability to destroy this one hippocampal cell type noninvasively made it possible to address the role of the dentate granule cells in learning and memory. Four months after ADX, 31 of 45 rats failed to show obvious granule cell loss and displayed behavior in the Morris water maze that was similar to 16 sham-operated control rats and 16 ADX rats maintained on corticosterone throughout the study. Conversely, 14 of the 45 ADX rats experienced a loss of granule cells that varied from minimal to extensive. Although there were no obvious differences between groups in motoric and motivational characteristics or search strategies, ADX rats with moderate to extensive granule cell loss acquired place learning slightly slower than controls or ADX rats with minimal or no obvious cell loss. Furthermore, the ADX rats with moderate to extensive cell loss were temporarily impaired following alteration of either intramaze or extramaze cues compared to controls. In contrast, the rats with granule cell loss remembered an old place and learned a new place as quickly as controls. These results suggest that a normal complement of dentate granule cell may not be necessary for the acquisition or retention of spatial information in the Morris water maze.

Spatial and temporal factors in the role of prefrontal and parietal cortex in visuomotor integration.

The effects of reversible lesion--by cooling--of dorsolateral prefrontal and posterior parietal cortex were studied in rhesus monkeys performing a cognitive visuomotor integration task. Correct performance required the use of a learned set of cue-response contingencies, some spatial and some nonspatial; in some cases, the task required the short-term retention, through a delay, of the color of the cue or its implicit response direction. Prefrontal cooling impaired performance of the task regardless of its spatial demands, an effect that increased with delay. Parietal cooling, on the other hand, only impaired performance if the task demanded the processing and retention of spatial information (i.e., if spatial active memory was required). Parietal effects were not related to delay. Both prefrontal and, even more, parietal cooling increased response time in all task contingencies. Thus, the results dissociate the respective contributions of the prefrontal and the posterior parietal cortex to the temporal and spatial aspects of information processing in visuomotor performance. They indicate that posterior parietal areas participate in spatial processing and in active memory of spatial information, whereas prefrontal areas subserve a broader role of visuomotor processing and cross-temporal integration of both spatial and nonspatial information.

The effect of flumazenil on acquisition, retention, and retrieval of spatial information

The effect of flumazenil, a benzodiazepine-receptor antagonist, was evaluated in a spatial-reference memory procedure in a water maze. Flumazenil (1.0, 3.0, and 10.0 mg/kg, ip) did not modify acquisition of spatial information. Retention was similar between control and experimental rats 24 h after the training phase, as all groups showed bias to the target quadrant in a free swim trial. However, 10 days later, only flumazenil-injected rats (3.0 mg/kg) showed bias to the target quadrant. Flumazenil did not affect retrieval of spatial information in a group of well-trained rats. These results suggest that a benzodiazepine-receptor mediated endogenous mechanism is activated during learning of spatial tasks and that its blockade facilitates retention of spatial information.

Stimulus-specific mechanisms of visual short-term memory

The retention of spatial information in visual short-term memory was assessed by measuring spatial frequency discrimination thresholds with a two-interval forced-choice task varying the time interval between the two gratings to be compared. The memory of spatial frequency information was perfect across 10-sec interstimulus intervals. Presentation of a “memory masker” grating during the interstimulus interval may interfere with short-term memory. This interference depends on the relative spatial frequency of the test and masker gratings, with maximum interference at spatial frequency differences of 1–1.5 octaves and beyond. This range of interference with short-term memory is comparable to the bandwidth of sensory masking or adaptation. A change of the relative orientation of test and masker gratings does not produce interference with spatial frequency discrimination thresholds. These results suggest stimulus-specific interactions at higher-level representations of visual form.

The forgetting algorithm: How fragmentary knowledge of exemplars can abstract knowledge.

The position of Perruchet and Pacteau (1990, 1991) concerning what is retained about past exemplars when subjects implicitly learn an artificial grammar oscillates between two extremes (bigram information versus intact exemplars). On the other hand, THIYOS, the model proposed by Mathews, Druhan, and Roussel (1989), on the basis of classifier systems, is capable of finding optimal sets of features to retain through rule competition. It is argued that people implicitly generate abstract rules that cannot be explained in terms of retention of bigrams or larger chunks without retention of spatial information and that THIYOS integrates findings associated with prototype and exemplar models of induction

Further studies of pigeons’ spatial working memory in the open-field task

In Experiments 1 and 2, pigeons’ spatial working memory in an open-field setting was examined under conditions that differed in terms of working-memory load (number of sites visited prior to a retention test) at various delays between initial choices and the retention test. In Experiment 1, pigeons were tested under two conditions of memory load (three or five sites visited prior to the delay) and two delay intervals (15 and 60 min). Accuracy declined as a function of delay but was not affected significantly by memory load. In Experiment 2A, pigeons were tested under three conditions of memory load (two, four, or six sites visited prior to the delay). In separate phases, the delay was 2, 15, and 60 min. Accuracy was not affected by memory load in any of these phases. In Experiment 2B, three conditions of memory load (two, four, or six sites visited prior to the delay) were tested at two delays (2 and 60 min) within a test phase. Accuracy declined with increasing delay, but memory load again had no significant effects. These results are inconsistent with previous suggestions that pigeons’ retention of spatial information may decline as working-memory load is increased. In Experiment 3, cue-manipulation tests confirmed that pigeons’ choice behavior in the open-field task is controlled by memory for previously visitad room locations.

Testosterone fails to reverse spatial memory decline in aged rats and impairs retention in young and middle-aged animals

Recently, the vasopressin (AVP) innervation in the rat brain was shown to be restored in senescent rats following long-term testosterone administration. In order to investigate whether this restoration is accompanied by an improvement in learning and memory, both sham- and testosterone-treated young (4.5 months), middle-aged (20 months), and aged (31 months) male Brown-Norway rats were tested in a Morris water maze. All animals learned to localize a cued platform equally well, indicating that the ability to learn this task was not affected by sensory, motoric, or motivational changes with aging or testosterone treatment. There were no significant differences in retention following cue training. Subsequent training with a hidden platform in the opposite quadrant of the pool (place training) revealed impaired spatial learning in middle-aged and aged animals. Retention following place training was significantly impaired in the sham-treated aged rats as compared with sham-treated young rats. Testosterone treatment did not improve spatial learning nor retention of spatial information, but, on the contrary, impaired retention in young and middle-aged animals. The present results confirm earlier reports on an impairment of spatial learning and memory in senescent rats but fail to support a role of decreased plasma testosterone levels and central AVP innervation in this respect.

Spatial performance is severely impaired in rats with combined reduction of serotonergic and cholinergic transmission

A possible interaction between serotonergic and cholinergic neurotransmission was examined in relation to the performance of a spatial memory task. Blockade of cholinergic transmission with a high dose of atropine was sufficient to impair performance of a water maze task. A partial reduction of cholinergic transmission using a low dose of atropine had no effect on this performance. Reducing serotonin synthesis, using a specific inhibitor of tryptophane hydroxylase p-chlorophenylalanine (PCPA) also had no effect on performance of such a task. However, a combined treatment with a low dose of atropine and PCPA severely impaired the performance of rats in the water maze. The rats were impaired in both acquisition of the initial spatial task and in reacquisition of a new spatial position (= working memory). These findings suggest an interaction between cholinergic and serotonergic transmission in acquisition and retention of spatial information. Furthermore they propose that deficits in cognitive abilities, observed in aging or Alzheimer's disease, may result from the combined reduction in cholinergic and serotonergic transmission.

The alleviation of short-term retention decrements with reactivation

Retention of spatial information by rats was shown to decrease significantly over a 90-sec retention interval. However, this decrement was alleviated significantly when a reactivation or cueing treatment was presented during the 90-sec interval. Further, the rate of forgetting following reactivation was shown to be similar to that which occurs following original information input. The implications of these findings for information loss models of forgetting were discussed.