Intraseptal administration of bicuculline produces working memory impairments in the rat.

Male Sprague-Dawley rats, trained to perform a delayed-non-match-to-sample eight-arm radial maze task, were implanted with a single cannula aimed at the medial septal nucleus. A within-subjects design was utilized to examine the effects of intraseptal administration of bicuculline (0.5 micrograms) on performance of this task with 1- and 4-h delay intervals imposed between choices four and five. Administration of bicuculline immediately following the first four choices produced an impairment in maze performance at both a 1- and a 4-h delay interval. This treatment also produced an increase in latency per choice. Bicuculline-induced impairments were not observed when administered 2 h following the predelay session (2 h prior to testing). These data support previous observations that pharmacological manipulation of GABAergic activity within the septum modifies working memory processes.     

Damage to the retrosplenial cortex produces specific impairments in spatial working memory

Mounting evidence indicates that the retrosplenial cortex (RSP) has a critical role in spatial navigation. The goal of the present study was to characterize the specific nature of spatial memory deficits that are observed following damage to RSP. Rats with RSP lesions or sham lesions were first trained in a working memory task using an 8-arm radial arm maze. Rats were allowed 5 min to visit each arm and retrieve food pellets and a 5-s delay was imposed between arm choices. Consistent with previous research, rats with RSP damage committed more errors than controls. In particular, RSP-lesioned rats committed more errors of omission (failing to visit an arm of the maze), but there were no lesion effects on errors of commission (revisiting an arm). Neither group of rats exhibited a turn bias (i.e., always turning a certain direction when choosing an arm). At the end of the training phase of the experiment, both groups had reached asymptote and committed very few errors. In the subsequent test phase, a longer delay (30-s) was imposed during some sessions. Both control and RSP-lesioned rats continued to make few errors during sessions with the standard 5-s delay, but RSP-lesioned rats were impaired at the 30-s delay and committed more errors of commission, consistent with an increase in taxing spatial working memory.     

Working memory impairments in schizophrenia: a meta-analysis

Working memory (WM) deficit is a cardinal cognitive symptom of schizophrenia, but the differences among the tasks and measures used to assess WM make it difficult to compare across studies. The authors conducted a meta-analytic review to address 3 major questions: (a) Do patients with schizophrenia show WM deficits across diverse methodology; (b) Is WM deficit supramodal; and (c) Does the WM deficit worsen with longer delays? The results indicate that significant WM deficit was present in schizophrenia patients in all modalities examined. Increasing delay beyond 1 s did not influence the performance difference between schizophrenia patients and healthy control participants in WM. These results suggest that WM deficit in schizophrenia is modality independent and that encoding and/or early part of maintenance may be problematic.     

Understanding the role of mind wandering in stress-related working memory impairments

Mind wandering has been identified as a possible cause for stress-related working memory (WM) task impairments following laboratory stressors. The current study attempted to induce mind wandering regarding negative, positive, or neutral events using an expressive writing task and examined the impact on WM task performance. We examined the role of mind wandering in understanding the impact of life stress on WM. Additionally, we explored the role of thought suppression on the relationship between mind wandering and WM. One hundred and fifty participants completed WM measures before (Time 1) and after (Time 2) the writing manipulation. The writing manipulation did not alter mind wandering or WM task performance. Time 1 WM predicted mind wandering during the Time 2 WM task, which subsequently predicted poorer Time 2 WM task performance. The impact of daily life stress on WM was mediated by mind wandering. Trait levels of thought suppression moderated the impact of mind wandering on WM. Specifically, higher levels of suppression resulted in stronger negative impact of mind wandering on WM task performance. Findings are discussed in terms of the impact of mind wandering on WM task performance.     

Attachment and emotional memory: investigating the source and extent of avoidant memory impairments

Attachment avoidance has been associated with impairments in memory for material with emotional, attachment-related themes (e.g., loss). In the present study the author investigated the source and extent of these memory deficits by examining working memory capacity for attachment-related and nonattachment-related material. Avoidance was associated with deficits in working memory for positive and negative attachment-related stimuli. However, avoidance was unrelated to working memory capacity for nonattachment-related stimuli, both emotional and nonemotional. These findings are consistent with the proposal that avoidant individuals defensively limit the processing of potentially distressing information. Attachment anxiety was unrelated to working memory capacity across word type. Implications of the findings for defensive strategies and emotional memory are discussed.     

Repeated diazepam administration reversed working memory impairments and glucocorticoid alterations in the prefrontal cortex after short but not long alcohol-withdrawal periods

The study was designed to assess whether repeated administration of diazepam (Valium®, Roche)—a benzodiazepine exerting an agonist action on GABA_A receptors—may alleviate both the short (1 week, 1W) and long-term (6 weeks, 6W) deleterious effects of alcohol withdrawal occurring after chronic alcohol consumption (6 months; 12% v/v) in C57/BL6 male mice. More pointedly, we first evidenced that 1W and 6W alcohol-withdrawn mice exhibited working memory deficits in a sequential alternation task, associated with sustained exaggerated corticosterone rise and decreased pCREB levels in the prefrontal cortex (PFC). In a subsequent experiment, diazepam was administered i.p. for 9 consecutive days (1 injection/day) during the alcohol withdrawal period at decreasing doses ranging from 1.0 mg/kg to 0.25 mg/kg. Diazepam was not detected in the blood of withdrawn mice at the time of memory testing, occurring 24 hours after the last diazepam injection. Repeated diazepam administration significantly improved alternation rates and normalized levels of glucocorticoids and pCREB activity in the PFC in 1W but not in 6W withdrawn mice. Thus, repeated diazepam administration during the alcohol-withdrawal period only transitorily canceled out the working memory impairments and glucocorticoid alterations in the PFC of alcohol-withdrawn animals.     

Cannabis-associated impairments in the fading affect bias and autobiographical memory specificity

We investigated potential relationships between cannabis use and 2 phenomena associated with autobiographical remembering: the fading affect bias (FAB) and memory specificity. The FAB is an emotional affect regulation mechanism that is observed when the intensity of affect associated with experiencing negative memories fades faster than the intensity of affect associated with experiencing positive memories. Memory specificity refers to the level of detail with which events are recalled. No studies have examined the relationships between cannabis use, the FAB, and memory specificity simultaneously. Chronic cannabis users (N = 47) and non-users (N = 52) recalled and described positive and negative autobiographical events and rated the affective intensity for the events at the time of occurrence and at time of test. Participants retrieved additional memories using a sentence-completion recall task, which were coded for specificity. Cannabis users showed reduced fading affect for unpleasant events and reduced memory specificity compared to non-users.     

Reinstating study context produces unconscious influences of memory

Having read a word does more to benefit its later perceptual identification when many, rather than few, of the words in the test list have been previously read. Some have suggested that this proportion overlap effect is produced by an intentional use of recognition memory or recall in the perceptual identification task. Contrary to this account, we found that words that are easily recognized (words generated from an anagram at study) do not gain more from increasing overlap than do words that are poorly recognized (words read at study). These findings are problematic for claims that word perception relies on a module, such as a logogen system, that is separate from the rest of memory.     

Dose- and delay-dependent working/episodic memory impairments following intraventricular administration of ethylcholine aziridinium ion (AF64A).

The present study examined the effects of intraventricular administration of the cholinergic neurotoxin ethylcholine aziridinium ion (AF64A) on performance of a radial arm maze task. Male Sprague-Dawley rats were trained to perform a delayed-nonmatch to sample radial arm maze task in which a 1-h delay was imposed between the fourth and fifth arm selections. Following acquisition, animals were injected bilaterally with AF64A (1.5 or 0.75 nmol/side) or artificial cerebrospinal fluid into the lateral cerebral ventricles and allowed 7 days to recover before behavioral testing resumed. Significant dose- and delay-dependent impairments in the radial maze performance were observed in AF64A-treated rats as evidenced by fewer correct choices following the delay and by more errors to complete the task. Long-term testing in this task revealed significant recovery of memory performance. These findings indicate dose-dependent impairments in memory following intraventricular administration of AF64A and spontaneous behavioral recovery following such insult.     

Prospective memory in the rat

The content of prospective memory is comprised of representations of an action to perform in the future. When people form prospective memories, they temporarily put the memory representation in an inactive state while engaging in other activities, and then activate the representation in the future. Ultimately, successful activation of the memory representation yields an action at an appropriate, but temporally distant, time. A hallmark of prospective memory is that activation of the memory representation has a deleterious effect on current ongoing activity. Recent evidence suggests that scrub jays and non-human primates, but not other species, are capable of future planning. We hypothesized that prospective memory produces a selective deficit in performance at the time when rats access a memory representation but not when the memory representation is inactive. Rats were trained in a temporal bisection task (90 min/day). Immediately after the bisection task, half of the rats received an 8-g meal (meal group) and the other rats received no additional food (no-meal group). Sensitivity to time in the bisection task was reduced as the 90-min interval elapsed for the meal group but not for the no-meal group. This time-based prospective-memory effect was not based on response competition, an attentional limit, anticipatory contrast, or fatigue. Our results suggest that rats form prospective memories, which produces a negative side effect on ongoing activity.     

A vasopressin metabolite produces qualitatively different effects on memory retrieval depending on the accessibility of the memory

A vasopressin metabolite, AVP4-9, was injected 1 h prior to retention tests at 1, 6, 11, and 16 days after learning to test the hypothesis that the peptide exerts qualitatively different effects on memory retrieval depending on the accessibility of the memory. The findings provided strong support for this hypothesis: At a retention interval associated with excellent recall in control animals, pretest administration of AVP4-9 (3.0 micrograms/kg) significantly impaired memory, while this same treatment significantly improved recall at an interval associated with poor retention in controls. At retention tests associated with intermediate recall in controls, retrieval was not significantly affected by the peptide treatment. This pattern of results indicates that the peptide treatment is interacting with endogenous changes that correspond to the accessibility of the memory.     

Detection of feigned memory impairments using a Chinese word task

In this study the detection of feigned memory impairments was investigated using a forced-choice task with Chinese words as stimuli. Task difficulty on accuracy and response time and the faking strategies employed were examined for 85 participants, 42 men and 43 women, who were administered the experimental task. Following a simulation design, all participants performed under control and faking conditions. Their accuracy of performance and response times were measured. Analysis indicated significant differences on both outcome measures for the two conditions. Further, a significant difference in accuracy, but not in response time, among levels of task difficulty was observed. For classification accuracy, using the cut-off score criterion seemed more effective than using the below-chance criterion or response time. Implications for relying on chance criterion to identify deception are discussed.     

Investigating semantic memory impairments: The contribution of semantic priming

Abstract

The semantic priming task is a valuable tool in the investigation of semantic memory impairments in patients with acquired disorders of language. This is because priming performance reflects automatic or implicit access to semantic information, unlike most other tests of semantic knowledge, which rely on explicit, voluntary access. Priming results are important for two main reasons: First, normal priming results may be observed in patients who perform poorly on other semantic memory tests, enabling us to distinguish between loss of, or damage to, information in semantic memory, and voluntary access to that information. Second, we can investigate the detailed pattern of loss and preservation of different types of semantic information, by charting the priming effects for different kinds of words, and different kinds of semantic relations between primes and targets.

We discuss the use of the priming task in this context, and address some of the theoretical and methodological criticisms that have been raised in connection with use of the priming task to address these issues. We then describe two recent studies in which we have employed semantic priming tasks, along with other more traditional methods, to investigate specific questions about the semantic memory deficits of three patients.     

Working memory impairments in children with specific arithmetic learning difficulties.

Working memory impairments in children with difficulties in arithmetic have previously been investigated using questionable selection techniques and control groups, leading to problems concluding where deficits may occur. The present study attempted to overcome these criticisms by assessing 9-year-old children with difficulties specific to arithmetic, as indicated by normal reading, and comparing them with both age-matched and ability-matched controls. A battery of 10 tasks was used to assess different aspects of working memory, including subtypes of executive function. Relative to age-matched controls, children with poor arithmetic had normal phonological working memory but were impaired on spatial working memory and some aspects of executive processing. Compared to ability-matched controls, they were impaired only on one task designed to assess executive processes for holding and manipulating information in long-term memory. These deficits in executive and spatial aspects of working memory seem likely to be important factors in poor arithmetical attainment.     

Working memory deficits in poor comprehenders reflect underlying language impairments.

Three experiments assessed memory skills in good and poor comprehenders, matched for decoding skill. Experiments 1 and 2 investigated phonological and semantic contributions to short-term memory by comparing serial recall for words varying in length, lexicality, and concreteness. Poor comprehenders showed normal sensitivity to phonological manipulations (length and lexicality) but, consistent with their semantic weaknesses, their recall of abstract words was poor. Experiment 3 investigated verbal and spatial working memory. While poor comprehenders achieved normal spatial spans, their verbal spans were impaired. These results are discussed within a theoretical framework in which the memory difficulties associated with poor reading comprehension are specific to the verbal domain and are a concomitant of language impairment, rather than a cause of reading comprehension failure.     

Assessment of short-term verbal memory impairments in adolescents and adults with ADHD

The purpose of this study was to determine whether a brief measure of verbal memory can assess short-term verbal memory impairments relative to verbal abilities in adolescents and adults with Attention-Deficit/Hyperactivity Disorder (ADHD) and to ascertain whether significant differences between short-term verbal memory and verbal abilities are more common among persons with ADHD than in the general population. One hundred seventy-six adolescents and adults diagnosed with ADHD (DSM-IV criteria) were assessed with a measure of short-term verbal memory. The short-term verbal memory score of each subject was compared with the verbal abilities on two measures. Percentages of ADHD subjects with "significant discrepancy" between verbal IQ and short-term verbal memory were compared with the standardization sample for the verbal memory measure. A majority of adolescents and adults diagnosed with ADHD demonstrated significant discrepancy between performance on the short-term verbal memory measure and verbal IQ. The percentage of ADHD subjects with a significant discrepancy between these two measures greatly exceeded the percentage of persons in the general population showing such a discrepancy. This brief measure of short-term verbal memory may be a useful measure to include in a comprehensive assessment for ADHD symptoms in adolescents and adults. Replication in other groups of ADHD patients is needed to test the generalizability of the findings.     

Short-term flavour memory in the rat

In a series of experiments, rats were exposed twice to a flavour at times T1 and T2, and the second of these exposures was followed by toxicosis. The level of the subsequent aversion was viewed as an index of whether the flavour had been recognised as familiar at T2, with a familiar flavour accruing less aversiveness than an unfamiliar one. A flavour was recognised as familiar at time T2 after a long flavour-exposure at time T1 (Experiment Ia) when moderate (3·5 h) and long (27·5 h) T1-T2 intervals were employed but was so recognised after a brief exposure at T1 (Experiment Ib) only when a moderate T1-T2 interval was employed. The memorial processes underlying flavour recognition after a brief flavour exposure were assumed, therefore, to be transient. The remaining experiments employed a brief flavour exposure at T1 and moderate T1-T2 intervals in various attempts to disrupt flavour recognition. Recognition at T2, however, was not disrupted when one (Experiment II), or three (Experiment IV) distractor flavours were interpolated between the target flavour's presentations at T1 and T2. This failure was not due to the distractor having proactively interfered with the associability of the target flavour with illness at T2 (Experiment III). Further, recognition was not disrupted when the position of the target flavour's presentation at T1 was varied across a list of distractor flavours (Experiment V), nor when the similarity of the distractor and the target flavour was varied (Experiment VI). The results indicate that the processes subserving recognition after a brief presentation of that flavour, although transient, are resistant to interference and were discussed in terms of current theories of short-term memory in animals.     

Category length produces an inverted-U discriminability function in episodic recognition memory

Four experiments used signal detection analyses to assess recognition memory for lists of words consisting of differing numbers of exemplars from different semantic categories. The results showed that recognition memory performance, measured by d _a , (a) increased as category length (CL, the number of study-list items selected from the same semantic category) increased from 1 to 8 but then decreased as CL further increased from 8 to 14, (b) was greater when 2 studied items from the same category occurred back to back, rather than being separated by 5–11 items from other categories, and (c) was greater for the first studied 2 exemplars than for the last studied 2 exemplars from blocked categories with CLs of 8 or 14. For all CLs, all z-coordinate receiver operating characteristic (z-ROC) functions were linear with slopes significantly less than 1.0, and none had a significant quadratic component. These results pose a challenge for three major classes of recognition memory models: item-noise, context-noise, and dual-process models.     

Oxotremorine attenuates retrograde amnesia induced by post-training administration of the GABAergic agonists muscimol and baclofen.

These experiments examined the involvement of cholinergic influences in the effects of GABAergic drugs on 24-h retention of an inhibitory avoidance response by mice. A first set of experiments confirmed previous findings indicating that post-training injections (ip) of the GABAergic agonists muscimol (1.0 and 2.0 mg/kg) and baclofen (10.0 and 20.0 mg/kg) impaired retention, as well as previous findings indicating that injections of the cholinergic agonist oxotremorine (5.0 and 10.0 micrograms/kg) enhanced retention. The findings of a second set of experiments indicated that the memory-impairing effects of muscimol and baclofen were attenuated by concurrent injections of a low, and otherwise ineffective, dose of oxotremorine (2.5 micrograms/kg). These findings are interpreted as suggesting that GABAergic drugs affect memory storage through influences on cholinergic systems.