Hippocampal lesions cause forgetting in a spatial response task

Monkeys with lesions to the hippocampus and overlying cortex were impaired in making a spatially selective response on the basis of a spatial cue. Their impairment was even more severe on a task in which they were required to make spatial responses on the basis of cues which are not spatially distinct. A second experiment showed that once lesioned monkeys had been trained on a task with spatially distinct stimuli, they were initially able to perform accurately if the aspatial distinctiveness of the cue was reduced. However, their performance declined to chance over four to six trials. These results suggest that lesions to the hippocampus and overlying cortex may cause impairments in memory for the arrangement of visual scenes, including the spatial location of responses. Keywords: spiny neurons, direct pathway, indirect pathways, rat neostriatum     

Prospective memory and task interference in a continuous monitoring dynamic display task.

Theories and methods from the prospective memory literature were used to anticipate how individuals would maintain and retrieve intentions in a continuous monitoring dynamic display task. Participants accepted aircraft into sectors and detected aircraft conflicts during an air traffic control simulation. They were sometimes required to substitute new actions for routine actions when accepting aircraft traveling at certain speeds or altitudes, or with certain call signs. In Experiment 1, prospective memory error increased with intent to deviate from strong compared to weak routine, and this effect was larger for altitude intentions compared to speed intentions. In addition, errors increased when intentions were general compared to specific. Participants also missed more conflicts when deviating from strong compared to weak routine. In Experiment 2, errors increased for intentions nonfocal to ongoing tasks compared to focal, and this effect was larger for altitude intentions compared to call sign intentions. Participants were slower to accept aircraft when holding nonfocal compared to focal intentions, and slower to accept aircraft and detect conflicts when holding focal intentions compared to no intentions. These findings are consistent with theories that assume that individuals allocate limited-capacity attentional resources to prospective memory tasks. Increased error for altitude intentions, together with the effect of routine strength, suggest a vulnerability to error with increased strength of association between prospective memory cues and competing ongoing tasks. Ongoing tasks that focus attention on cues may sometimes impair, rather than benefit, intention retrieval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of forgetting in an implicit and explicit memory task.

Among possible criteria for distinguishing separate memory systems for implicit and explicit memory is that of substantial differences in either the form or rate of forgetting. Prior literature has claimed both differential forgetting and equivalent forgetting for implicit and explicit tasks. Existing experimental data for word-stem completion and explicit control tasks were reviewed and shown to be inconclusive. Our experiments measure forgetting in comparable implicit and explicit memory tasks of stem completion and stem cued recall. The form and the rate of forgetting are essentially the same for these implicit and explicit tasks. Levels of processing and task conditions differ only in the level of initial learning or availability. Thus, either the implicit and explicit task reflect traces in the same memory system or they reflect traces in different systems that have identical forgetting dynamics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retrieval-induced forgetting in a category recognition task.

Prior work on retrieval-induced forgetting showed that retrieving a subset of formerly studied items can impair item recognition of related, nonretrieved material. Here it was investigated whether retrieval practice can also impair the items' recognition as a member of a studied category. Subjects studied preexperimentally unrelated words that were categorized by their font colors, then practiced retrieving a subset of the words using a word stem completion task. Finally, an episodic category recognition test based on confidence ratings was applied. Receiver operating characteristic analysis of the data demonstrated a reliable impairment in subjects' recognition of the nonretrieved items' category relative to control items. The result indicates that retrieval-induced forgetting is not restricted to item recognition but generalizes to category recognition tasks. Inhibitory as well as noninhibitory explanations of the finding are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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.     

Estradiol enhances learning and memory in a spatial memory task and effects levels of monoaminergic neurotransmitters

Calretinin (CaR) is a calcium-binding protein that is distributed extensively in the central nervous system. It is localized in the cell bodies and neurites of specific neuronal populations and serves, therefore, as a reliable anatomical marker. Some components of the pretectocerebellar projection, which connects specific pretectal nuclei to caudal cerebellar folia, are concerned with the cerebellar control of visual reflexes. We investigated the distribution of pretectocerebellar-projecting neurons in relation to cells that show CaR immunoreactivity. Cells that project to the cerebellar cortex in the diencephalic primary visual nuclei and in other grisea, like the nucleus spiriformis medialis and the nucleus dorsofrontalis, colocalized with those that appeared to be immunolabeled intensely with anti-CaR antiserum. To explore the hypothesis of a common developmental origin of these pretectal cerebellopetal neurons, we also investigated the development of CaR-immunopositive cells in the chick pretectum and the arrival of their fibers in the cerebellum, from 10 days of incubation (stage 36) to posthatching stages. Finally, we analyzed the source of CaR+ climbing fibers and found a subpopulation of CaR+ cells in the inferior olivary nucleus. On the whole, these results suggest that there is a common developmental origin of pretectal cerebellopetal neurons, some of which share the property of CaR expression. The functional significance of this correlation needs to be investigated.     

Redistribution of spatial representation in the hippocampus of aged rats performing a spatial memory task.

Young and old rats performed on a maze according to a forced-choice and then a spatial memory procedure either in the same or a different environment. Aged rats were slower to learn the spatial memory task when tested in the same, but not in a different, room. One interpretation of this pattern of results is that although old rats learn new rules as quickly as young rats, they show less flexibility with old rules and familiar spatial information. Impaired choice accuracy during asymptote performance suggests poor processing of trial-unique information by old rats. Spatial correlates of hippocampal CA1 and hilar cells varied with task demand: CA1 cells of aged rats showed more spatially selective place fields, whereas hilar cells showed more diffuse location coding during spatial memory, and not forced-choice, tests. Such representational reorganization may reflect a compensatory response to age-related neurobiological changes in the hippocampus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Medial septal lesions in rats produce permanent deficits for strategy selection in a spatial memory task.

Rats with medial septal (MS) lesions have been shown to consistently use a stereotypic response strategy rather than a nonstereotypic spatial learning strategy when solving a radial maze task. The present study examined the long-term effects of MS lesions on spatial memory performance to determine whether MS lesions permanently impair rats from using a nonstereotypic strategy. Male rats, initially trained on a radial maze, were given either MS or sham surgeries and were subsequently retested on the maze. Consistent with previous studies, all Ss with MS lesions used a stereotypic strategy during the postoperative retest. However, when placed through a series of retraining phases that required the S to use a nonstereotypic strategy to solve the task, none of the MS Ss could solve the task. These results indicate that lesions of the MS produce permanent spatial memory deficits that cannot be restored through extensive behavioral training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working memory and the control of action: Evidence from task switching.

A series of 7 experiments used dual-task methodology to investigate the role of working memory in the operation of a simple action-control plan or program involving regular switching between addition and subtraction. Lists requiring switching were slower than blocked lists and showed 2 concurrent task effects. Demanding executive tasks impaired performance on both blocked and switched lists, whereas articulatory suppression impaired principally the switched condition. Implications for models of task switching and working memory and for the Vygotskian concept of verbal control of action are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Similarities and differences between working memory and long-term memory: Evidence from the levels-of-processing span task.

Two experiments compared the effects of depth of processing on working memory (WM) and long-term memory (LTM) using a levels-of-processing (LOP) span task, a newly developed WM span procedure that involves processing to-be-remembered words based on their visual, phonological, or semantic characteristics. Depth of processing had minimal effect on WM tests, yet subsequent memory for the same items on delayed tests showed the typical benefits of semantic processing. Although the difference in LOP effects demonstrates a dissociation between WM and LTM, we also found that the retrieval practice provided by recalling words on the WM task benefited long-term retention, especially for words initially recalled from supraspan lists. The latter result is consistent with the hypothesis that WM span tasks involve retrieval from secondary memory, but the LOP dissociation suggests the processes engaged by WM and LTM tests may differ. Therefore, similarities and differences between WM and LTM depend on the extent to which retrieval from secondary memory is involved and whether there is a match (or mismatch) between initial processing and subsequent retrieval, consistent with transfer-appropriate-processing theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence of location memory in 8-month-old infants in a nonsearch AB task.

Recent studies have shown that when an object is hidden in a location A and then in a location B, 8-month-old infants tend to search in A if forced to wait 3 s before retrieving the object, and to search randomly in A or B if forced to wait 6 s before retrieving the object (e.g., Diamond, 1985). A non-search method was devised to examine 8-month-olds' ability to remember the location of a hidden object. The infants saw an object standing on one of two placemats located on either side of the midline. Next, screens were pushed in front of the placemats, hiding the object from view. After 15 s, a hand reached behind one of the screens and reappeared holding the object. The infants looked reliably longer when the hand retrieved the object from behind the "wrong" as opposed to the "right" screen (where the object was actually hidden). This result suggests that the infants (a) remembered the object's location during the 15-s delay and (b) were surprised to see the object retrieved from behind the right (left) screen when they had last seen it on the left (right) placemat. These results indicate that 8-month-old infants' ability to remember the location of a hidden object is far better than their performance in the AB search task suggests. As such, the present results cast serious doubts on accounts that attribute infants' perseverative and/or random search errors to limited memory mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retrieval-induced forgetting in episodic memory.

Participants learned the locations of 12 stimuli that were uniquely colored but could be grouped by shape (4 circles, 4 triangles, 4 crosses). Following the study, a retrieval-practice phase required participants to recall the colors of a subset of the stimuli (i.e., 2 circles, 2 triangles) using shape and location as cues. In a final test, participants recalled the colors of all 12 stimuli. Compared with the control set of stimuli (i.e., 4 crosses), memory was facilitated for practiced items but impaired for related items, which were not practiced but shared the same shape group. Across experiments, retrieval-induced forgetting was observed for different perceptual groupings and for different cuing procedures. The effect, however, required retrieval of information during the interpolated phase. Providing extra presentations did not disrupt memory for related items. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Repetition blindness for locations: Evidence for automatic spatial coding in an RSVP task.

The authors report a new phenomenon called repetition blindness (RB) for locations: When 3 or 4 letters are presented rapidly and sequentially at random locations within a spatial array, experimental participants have difficulty reporting pairs of letters appearing in the same location within 250 ms of each other. This deficit occurs both during report of letter identities and during report of the locations in which the letters appear; it can also be found using a partial report task. During letter report, the deficit is found for 4-location arrays bit not for 8-location arrays. In contrast, letter RB is not found during location report even when the letters are always chosen from a set of 4. These results indicate that a small number of locations-but not letters-can be encoded automatically even when they are not explicitly reported. The authors argue that RB for locations results from a difficulty individuating 2 tokens at the same spatial location. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gorillas' (Gorilla gorilla gorilla) spatial memory in a foraging task.

The spatial memory of 2 gorillas (Gorilla gorilla gorilla) was explored in a simulated foraging task. Trials consisted of 2 parts separated by a delay. In the 1st part, half of the total number of food sites were baited with a highly preferred food, and the subject was allowed to search, find, and consume these items (search phase). During the delay the same locations were again baited. After the delay the animal was reintroduced to the test enclosure and allowed to search through the sites again (re-search phase). In Exp 1, an adult gorilla was very accurate in remembering locations that had previously contained food at delay intervals of 24 hrs or more. In Exp 2, a juvenile gorilla was also accurate in remembering locations that had previously contained food at delays up to 10 min. The adult gorilla appeared to use a counting strategy during the search phase to minimize the number of sites visited. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence for spatial working memory in honeybees (Apis mellifera).

Spatial working memory (the ability to represent multiple locations in a flexible, dynamic manner) has been studied in a range of vertebrate species. The results of 3 experiments indicate that this ability also exists in at least one invertebrate (honeybees; Apis mellifera). Individual honeybees collected sugar solution from a matrix of 6 locations. They avoided revisits to locations previously depleted of solution more accurately than expected by chance. The results rule out several nonmemorial explanations for this ability, and it is therefore best explained by a spatial working memory system that allows discrimination of previously visited locations from those not yet visited. These results substantially expand the range of species in which spatial working memory has been demonstrated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response-contingent variation in visual recall: Evidence of a dynamic memory trace.

Conducted an experiment to confirm hypotheses derived from D. C. Donderi (1973) and Donderi et al (1970) that visual memory is sensitive to information in learned stimulus-response contingencies and to the delay in recall testing. 66 Ss (aged 19–26 yrs) learned responses to 4 ellipses that varied orthogonally in area and orientation. Correct responses were contingent on either area or orientation of the ellipses. Ss recalled the ellipses by drawing them. Findings confirm that there was a systematic change in recall memory along a stimulus dimension when values along that dimension were associated with responses that were learned to the set of stimuli prior to recall. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

GluR-A-deficient mice display normal acquisition of a hippocampus-dependent spatial reference memory task but are impaired during spatial reversal.

Acquisition and reversal of a spatial discrimination were assessed in an appetitive, elevated plus-maze task in 4 groups of mice: knockout mice lacking the AMPA receptor subunit GluR-A (GluR1), wild-type controls, mice with cytotoxic hippocampal lesions, and controls that had undergone sham surgery. In agreement with previous studies using tasks such as the water maze, GluR-A-/- mice were unimpaired during acquisition of the spatial discrimination task, whereas performance in the hippocampal group remained at chance levels. In contrast to their performance during acquisition, the GluR-A-/- mice displayed a mild deficit during reversal of the spatial discrimination and were profoundly impaired during discrete trial, rewarded-alternation testing on the elevated T maze. The latter result suggests a short-term. flexible spatial working memory impairment in GluR-A-/- mice, which might also underlie their mild deficit during spatial reversal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characteristics of basolateral amygdala neuronal firing on a spatial memory task involving differential reward.

Previous research has shown that spatial, movement, and reward information is integrated within the ventral striatum (VS). The present study examined the possible contribution of the basolateral nuclei of the amygdala (BLA) to this interaction by examining behavioral correlates of BLA neurons while rats performed multiple memory trials on an 8-arm radial maze. Alternate arms consistently held 1 of 2 different amounts of reward. Recorded cells were correlated with motion, auditory input, space, and reward acquisition. Reward-related units were found that anticipated reward encounter, that responded during reward consumption, and that differentiated between high and low reward magnitude. This is consistent with the hypothesis that BLA neurons may provide the VS with reward-related information that could then be integrated with spatial information to ultimately affect goal-directed behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)