Recognition Memory Task Research Articles

Orienting and memory to unexpected and/or unfamiliar visual events in children and adults

For children, new experiences occur very often, and learning to differentiate between old and new events is a fundamental process necessary for appropriate reactions to stimuli. Thus the present study is concerned with maturation of brain responses to repeated novel events. We examined the effect of repetition of familiar (meaningful) and unfamiliar (meaningless) symbols on the event-related-potentials (ERPs) recorded during novelty oddball and recognition memory tasks from children, adolescents and young adults. During the novelty oddball task, repetition of the familiar symbols elicited a reduction in the novelty P3 in the ERPs of all age groups, while repetition of the unfamiliar symbols elicited a reduction in novelty P3 amplitude only in children. As expected, recognition memory performance improved with age and was better for familiar than unfamiliar symbols. For all age groups, ERPs to correctly recognized familiar old symbols elicited a larger positivity than ERPs to correctly identified new symbols, indicating a reliable memory effect. However, ERPs to unfamiliar old and new symbols did not differ in adults and adolescents but did differ in children. The data suggest that children process familiar visual symbols in a similar fashion to that of adults, and that children process unfamiliar symbols differently from adults.

Unique contribution of semantic representations to immediate memory: an individual-differences approach

ABSTRACTStudies have reported dissociations between the contributions of semantic and phonological representations to immediate remembering, found through experimental manipulations as well as specific clinical cases. Also, some studies based on the analysis of individual differences reported that a semantic cued recall task has a variance unshared with the immediate memory tasks which tap the contribution of phonological representations. However, another study suggested that cued recall performance could reflect a wider ability to cluster information by category. Furthermore, no studies of individual differences have investigated the unique semantic contribution in the visual domain. Therefore, the present study used specific immediate recognition memory tasks that have been used to investigate the semantic contribution in the verbal and visual domains. The results demonstrate the unshared variance that reflects the semantic contribution in both the verbal and the visual domain, and some commonality in these variances across the domains.

Differential Outcomes Training Ameliorates Visual Memory Impairments in Patients With Alzheimer's Disease: A Pilot Study.

It is well known that Alzheimer’s disease (AD), the most common form of dementia, is associated with deficits in cognitive processes including visual memory impairments. One technique that might be used to ameliorate these impairments is the differential outcomes procedure (DOP) that involves associating each to-be-remembered stimulus with a specific outcome.Objective: Previous research has demonstrated that the DOP can be used to reduce or eliminate the learning and memory deficits associated with animal models of amnesia and dementia. Furthermore, this procedure has been shown to improve delayed facial recognition in healthy older adults as well as in patients diagnosed with AD. The main aim of the present study is twofold: to extend these findings to other types of visual stimulus and to investigate the effect of the DOP in memory retention in AD patients.Method: Ten patients diagnosed with AD and 10 healthy controls participated in this study. The experiment included two phases. In the first one, they had to perform a delayed matching-to-sample task. In the second phase, participants performed a recognition memory task, designed to assess long-term retention, 1 h and 1 week after the training.Results: Participants showed a better memory-based performance as well as a higher long-term retention of the information when trained under the differential outcomes condition, relative to the non-differential outcomes condition.Conclusions: The DOP seems to be an effective, easy-to-implement, technique to enhance visual memory in AD patients.

M48 - DECONSTRUCTING THE NEUREXIN1 DELETION PHENOTYPE: A NEUROPSYCHOLOGICAL, NEUROCOGNITIVE AND NEUROIMAGING PERSPECTIVE

Background The Neurexin1 (NRXN1; 2p16.3) gene has been identified as a rare but significant genetic risk factor for neurodevelopmental disorders including Autism Spectrum Disorder (ASD) schizophrenia, Intellectual Disability (ID) and bipolar disorder. NRXN1 encodes Neurexins, neuronal adhesion molecules on axon terminals, which bind postsynaptic Neuroligins (encoded by NLGN). The primary function of NRXN1 is to stabilise synapse formation and facilitate neuronal transmission. Common clinical features are associated with NRXN1 deletions but these have not been deconstructed using in-depth neuropsychological, neurocognitive and neuroimaging techniques. This project aims to deep phenotype individuals and characterise the clinicopathological features of NRXN1 deletions. Methods 21 participants with NRXN1 deletions and 21 age and gender matched controls were recruited. Semi-structured neuropsychological assessments (CAPA, PAS-ADD) were performed and questionnaires to probe for existing and/or sub-threshold psychiatric disorders or symptoms were collated. The Wechsler Abbreviated Scale of Intelligence-second edition (WASI-II) and a comprehensive cognition battery (CANTAB; http://www.cambridgecognition.com/) was administered to all participants to assess neurocognitive functioning. High Angular Resolution Diffusion Imaging (HARDI) data (61 directions, b-value=1500 s/mm2) were acquired (n=17 per group) to evaluate neuroanatomical differences. Preprocessing was completed using ExploreDTI software (http://www.ExploreDTI.com). Data quality checks were performed and subject motion and eddy current induced geometric distortions were corrected for in one interpolation step to minimise blurring effects. Fractional anisotropy (FA) values were extracted and voxelwise statistical analysis of the FA data was carried out using Tract-Based Spatial Statistics (TBSS) in FSL ( https://fsl.fmrib.ox.ac.uk/fsl ). Results The groups did not differ in age (t(40)=-0.015, p=0.988) but there was a significant difference in IQ (t(40)=-6.3, p=0.00) thus IQ was included as a covariate in all statistical analyses. Neuropsychological assessments indicated that 6 individuals have met criteria for ASD, 3 for mild ID, 2 for ADHD, 1 for a psychotic disorder and 1 for a conduct disorder. Neurocognitive assessments indicate a trend towards executive dysfunction and aberrant social cognition in individuals with NRXN1 deletions characterised by greater number of errors on spatial working memory, spatial organisation and emotion recognition tasks, p Discussion Interesting clinical characteristics of NRXN1 deletions are emerging. This study indicates that NRXN1 deletions may contribute to neurocognitive deficits related to executive functioning and social cognition, two domains that are consistently described as aberrant in neurodevelopmental disorders. Furthermore, individuals with NRXN1 deletions demonstrate a pattern of disrupted structural connectivity, which has also been described in neurodevelopmental disorders such as ASD and schizophrenia. Further clinical and neurobiological phenotyping in addition to mapping of the NRXN1 genotype may elucidate the underlying neurobiological processes contributing to neurodevelopmental disorders.

Lexical knowledge boosts statistically-driven speech segmentation.

The hypothesis that known words can serve as anchors for discovering new words in connected speech has computational and empirical support. However, evidence for how the bootstrapping effect of known words interacts with other mechanisms of lexical acquisition, such as statistical learning, is incomplete. In 3 experiments, we investigated the consequences of introducing a known word in an artificial language with no segmentation cues other than cross-syllable transitional probabilities. We started with an artificial language containing 4 trisyllabic novel words and observed standard above-chance performance in a subsequent recognition memory task. We then replaced 1 of the 4 novel words with a real word (tomorrow) and noted improved segmentation of the other 3 novel words. This improvement was maintained when the real word was a different length to the novel words (philosophy), ruling out an explanation based on metrical expectation. The improvement was also maintained when the word was added to the 4 original novel words rather than replacing 1 of them. Together, these results show that known words in an otherwise meaningless stream serve as anchors for discovering new words. In interpreting the results, we contrast a mechanism where the lexical boost is merely the consequence of attending to the edges of known words, with a mechanism where known words enhance sensitivity to transitional probabilities more generally.

Divided Attention Selectively Impairs Value-Directed Encoding

In the present study, we examined the effect of value-directed encoding on recognition memory and how various divided attention tasks at encoding alter value-directed remembering. In the first experiment, participants encoded words that were assigned either high or low point values in multiple study-test phases. The points corresponded to the value the participants could earn by successfully recognizing the words in an upcoming recognition memory task. Importantly, participants were instructed that their goal was to maximize their score in this memory task. The second experiment was modified such that while studying the words participants simultaneously completed a divided attention task (either articulatory suppression or random number generation). The third experiment used a non-verbal tone detection divided attention task (easy or difficult versions). Subjective states of recollection (i.e., “Remember”) and familiarity (i.e., “Know”) were assessed at retrieval in all experiments. In Experiment 1, high value words were recognized more effectively than low value words, and this difference was primarily driven by increases in “Remember” responses with no difference in “Know” responses. In Experiment 2, the pattern of subjective judgment results from the articulatory suppression condition replicated Experiment 1. However, in the random number generation condition, the effect of value on recognition memory was lost. This same pattern of results was found in Experiment 3 which implemented a different variant of the divided attention task. Overall, these data suggest that executive processes are used when encoding valuable information and that value-directed improvements to memory are not merely the result of differential rehearsal.

Cortical thickness, neurocognitive, and body composition effects of fasting during Ramadan.

Background:We aimed to study the anatomical, physiological, and cognitive function of healthy individuals practicing fasting during the month of Ramadan. Measurements were taken 1 week before and 2 weeks after Ramadan fasting.Materials and Methods:Twelve healthy male individuals (mean age ± standard error of the mean: 34.3 ± 2.9 years; body mass index: 26.26 ± 1.4 kg/m2) were assessed for various parameters before and after Ramadan fasting. All the tests were performed in the morning. Body composition characteristics were assessed by bioelectrical impedance analysis using a commercially available body composition analyzer. For neurocognitive analysis, participants underwent the stop signal task (SST), pattern recognition memory task (PRM), and spatial working memory strategy (SWM) from the Cambridge Neuropsychological Test Automated Battery. T1-weighted, 1 mm-thick magnetic resonance images were also acquired.Results:Anthropometric analysis showed a significant decrease in body weight, fat-free mass (FFM), trunk FFM, and trunk predicted muscle mass, while the other body composition parameters did not exhibit any changes. The stop signal reaction time (SSRT) latency (ms) (P > 0.05) and PRM did not show any significant difference before and after fasting. SWM task (P < 0.05) improved significantly after fasting. Cortical thickness data of the whole brain were not significantly different after fasting at any brain location. There was a significant correlation between the left amygdala and the SWM strategy (r2 = 0.518) and between fat and brain segmentation volume (r2 = 0.375).Conclusion:Our pilot data suggest that Ramadan fasting leads to weight loss and FFM reductions and improve cognitive function.

Experimental Effects of Acute Exercise on Source Memory Recognition

Previous work suggests that acute exercise may enhance episodic memory function. However, no study has evaluated whether acute exercise can enhance source memory recognition, which was the purpose of this study. A two-arm, parallel-group randomized controlled intervention was employed. The experimental group walked briskly for 15 minutes with a 5-minute seated recovery task (Sudoku), while the control group engaged in a time-matched (20-min) seated task (Sudoku). Subsequently, participants completed a source episodic memory task. The experimental group recalled more words than the control group (M = 6.35, SD = 2.99 and M = 5.30, SD = 2.83, respectively; P=0.26, d=0.36). However, there were no differences in performance on the source memory recognition task (discrimination index, -0.20 vs. 1.50, t=0.64, P=0.52, d=0.20). Our results provide some evidence of non-statistically small magnitude of an exercise-induced enhancement effect on episodic memory, but our findings did not suggest a beneficial source memory effect from acute exercise.

Flumazenil but not bicuculline counteract the impairing effects of anesthetic ketamine on recognition memory in rats. Evidence for a functional interaction between the GABAA-benzodiazepine receptor and ketamine?

Experimental evidence indicates that anesthetic doses of the non-competitive NMDA receptor antagonist ketamine impair memory abilities in rodents. The mechanism by which anesthetic ketamine produces its adverse behavioural effects is not yet clarified. In this context, it has been proposed that the effects of anesthetic ketamine on memory might be attributed to its agonistic properties on the GABA type A receptor. The present study was designed to address this issue. Thus, we investigated the ability of the benzodiazepine receptor antagonist flumazenil (1, 3, 6 mg/kg, i.p.) and the GABAA receptor antagonist bicuculline (0.5, 1.5, 3 mg/kg, i.p.) to counteract recognition memory deficits produced by anesthetic ketamine (100 mg/kg, i.p.) in rats. For this purpose, the novel object recognition task, a behavioural paradigm assessing recognition memory abilities in rodents was used. Compounds were coadministered 24 h before testing or retention. Pre (24 h before testing) or post-training (24 h before retention) administration of flumazenil (6 mg/kg, i.p.) counteracted anesthetic ketamine-induced performance deficits in the novel object recognition memory task. Conversely, bicuculline failed to attenuate the recognition memory deficits caused by anesthetic ketamine. Our findings propose a functional interaction between anesthetic ketamine and the GABAA receptor allosteric modulator flumazenil on recognition memory.

Distinct roles of eye movements during memory encoding and retrieval

A long line of research has shown that vision and memory are closely linked, such that particular eye movement behaviour aids memory performance. In two experiments, we ask whether the positive influence of eye movements on memory is primarily a result of overt visual exploration during the encoding or the recognition phase. Experiment 1 allowed participants to free-view images of scenes, followed by a new-old recognition memory task. Exploratory analyses found that eye movements during study were predictive of subsequent memory performance. Importantly, intrinsic image memorability does not explain this finding. Eye movements during test were only predictive of memory within the first 600 ms of the trial. To examine whether this relationship between eye movements and memory is causal, Experiment 2 manipulated participants’ ability to make eye movements during either study or test in a new-old recognition task. Participants were either encouraged to freely explore the scene in both the study and test phases, or had to refrain from making eye movements in either the test phase, the study phase, or both. We found that hit rate was significantly higher when participants moved their eyes during the study phase, regardless of what they did in the test phase. False alarm rate, on the other hand, was affected only by eye movements during the test phase: it decreased when participants were encouraged to explore the scene. Taken together, these results reveal a dissociation of the role of eye movements during the encoding and recognition of scenes. Eye movements during study are instrumental in forming memories, and eye movements during recognition support the judgment of memory veracity.

How does aging influence object-location and name-location binding during a visual short-term memory task?

Objective: Age-related impairments in human visual short-term memory (VSTM) may reflect a reduced ability to retain bound object representations, viz., object form, name, spatial, and temporal location (so called ‘memory sources’). Our objective is to examine how healthy aging affects VSTM in a battery of memory recognition tasks in which sequentially presented objects, locations, and names (as auditory stimuli) were learned, with one component cued at test.Methods: Thirty-six young healthy adults (18–30 years) and 36 normally aging older adults (>60 years with no underlying health and vision issues) completed five VSTM tasks: 1. Object recognition for two or four objects; 2. Spatial location recognition for two or four objects; 3. Bound object-location recognition for two or four objects; 4. Object recognition with location priming for two or four objects; 5. Bound name (auditory)-location (cross-modal) recognition for four objects.Results: Significantly lower performance for older adults was found in spatial location recognition [task 2, p = 0.03], bound object-location recognition [task 3, p = 0.001], object recognition with location priming [task 4, p = 0.02], and bound name-location recognition [task 5, p = 0.001, independent samples t-test] tasks. A significant age group-task interaction was found (p = 0.02).Conclusion: Performance for all tests except test 1 was impaired in older adults. Lower performance for older adults was most significant in VSTM tasks requiring object-location (visual only) or name-location (auditory and visual) binding. The findings are compatible with the ‘memory source’ model, demonstrating that age-related binding performance is influenced by spatial coding and location priming deficits.

Resting state functional connectivity and neural correlates of face-name encoding in patients with ischemic vascular lesions with and without the involvement of the left inferior frontal gyrus

Face-name association is a relevant ability for social interactions and involves the ventral and dorsolateral prefrontal cortices, particularly in the left hemisphere, bilateral hippocampal, fusiform gyrus and occipital regions. Previous studies demonstrated the primary role of the hippocampus for this ability in healthy subjects. However, no study has examined the participation of the left inferior frontal area, specially the left inferior frontal gyrus (LIFG) in patients with ischemic vascular lesions. In the present study we addressed this issue and investigated the neural correlates and resting state functional connectivity of face-name memory encoding in ischemic patients with LIFG or without lesions in the left IFG (nLIFG) and healthy controls (HC) using fMRI. The main results showed that the nLIFG group demonstrated efficient compensation related to encoding and performance on face-name learning and recognition memory task, in addition to similar brain areas activated during task performance compared to healthy controls. Some of these areas were more activated in nLIFG group, indicating a compensation mechanism. In contrast, the LIFG group showed worse behavior performance, and no signs of an efficient compensation mechanism. Functional connectivity analysis suggested that the left IFG region seems to be important for maintaining the connectivity of the right fusiform gyrus or, perhaps, lesion in this area is associated to maladaptive reorganization. Our findings highlight the relevant role of the left IFG in face-name learning and encoding, possibly as a primary region in addition to the bilateral hippocampal formation and fusiform gyrus.

Event-related potential correlates of recognition memory in asymptomatic individuals with CADASIL

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common form of hereditary stroke disorder and is caused by mutations of the NOTCH3 gene. Cognitive decline in CADASIL is characterized by early impairments of attention, memory, and executive functions. Studying asymptomatic individuals with CADASIL offers a unique genetic model to understand preclinical vascular cognitive impairment and dementia. This study aimed at examine whether early preclinical physiological changes could be observed in asymptomatic individuals with CADASIL, who will go on to develop vascular cognitive impairment and dementia later in life. Twenty-nine individuals (mean age: 54.1 years old) were included in the study; five CADASIL NOTCH3 mutation carriers and twenty-five age-matched non-carriers. Participants underwent a comprehensive clinical evaluation and neuropsychological testing. Event-related potentials (ERPs) were recorded during a picture recognition memory task. Analyses focused on the early frontal effect and parietal effect ERP components associated with familiarity and recollection memory. There were no differences between groups in behavioral performance during recognition memory discrimination or cognitive performance. Compared to non-carriers, CADASIL carriers had decreased amplitudes in both ERP components for hits and correct rejections. Among mutation carriers, lower amplitude at 500–600 ms in the left parietal region of interest for correct rejections was correlated with worse performance on measures of semantic fluency and inhibitory control. We conclude that cognitively unimpaired CADASIL carriers showed abnormalities in the neural correlates of recognition memory, years before clinical onset. Early disruptions of fronto-subcortical networks may explain preclinical changes in brain function during recognition memory. This work also demonstrates the potential usefulness of ERP brain correlates as preclinical markers of vascular dementia.

Making sense of sequential lineups: An experimental and theoretical analysis of position effects

Abstract As part of a criminal investigation, the police often administer a recognition memory task known as a photo lineup. A typical 6-person photo lineup consists of one suspect (who may or may not be guilty) and five physically similar foils (all known to be innocent). The photos can be shown simultaneously (i.e., all at once) or sequentially (i.e., one at a time). Approximately 30% of U.S. police departments have moved to using the sequential lineup procedure over the last 30 years, yet its theoretical underpinnings remain poorly understood. A simple signal detection model makes several unexpected predictions about how the sequential lineup procedure should affect the ability of eyewitnesses to discriminate innocent from guilty suspects. For example, empirical discriminability (area under the receiver operating characteristic) should decrease as the position of the suspect in the lineup increases. In addition, under some conditions, a fair sequential lineup should not yield higher discriminability than a single-person (non-lineup) recognition test known as a showup. The results of two experiments reported here confirmed these predictions. Counterintuitively, even though empirical discriminability decreased as the suspect’s sequential position increased, a signal detection model fit to the data indicated that theoretical discriminability exhibited a small effect in the opposite direction (increasing with the sequential position of the suspect). The latter result is consistent with diagnostic feature-detection theory of eyewitness identification.

Memory bias and its association with memory function in women with posttraumatic stress disorder

BackgroundMemory abnormalities are among a central feature of posttraumatic stress disorder (PTSD). It is suggested that individuals with PTSD exhibit memory bias; while evidence shows poor memory function in these individuals. We aimed to examine memory bias in PTSD patients relative to controls and to explore an association between memory bias and memory function. MethodsForty-six women with DSM-IV PTSD, most of whom developed the disorder after interpersonal violence, and 68 non-trauma-exposed healthy control women were studied. Memory bias was assessed by a recognition memory task using negative, neutral, and positive words. Memory function was assessed by a standardized neuropsychological test battery. Depression and anxiety symptoms were assessed by self-report measures. ResultsCompared to controls, patients showed significantly greater negative bias scores (i.e., correctly recognized rates for negative words minus those for neutral words) and poorer memory function. Negative bias scores were significantly correlated with worse memory function in patients. When patients were divided into those with lower vs. normal memory function, the former patients had significantly greater negative bias than the latter patients and controls. Memory bias scores in patients were not significantly correlated with depression or anxiety symptoms, nor were they significantly different between patients with comorbid major depressive disorder and those without. LimitationsThe cross-sectional design and absence of the trauma-exposed non-PTSD group limited our findings. ConclusionsPTSD patients have greater negative memory bias, which can be associated with poorer memory function. Our findings may provide an insight into the nature of memory abnormalities in PTSD.

Assessment of neuropsychological performance in Mexico City youth using the Cambridge Neuropsychological Test Automated Battery (CANTAB)

ABSTRACTBackground: The Cambridge Neuropsychological Test Automated Battery (CANTAB) is a computerized tool used to measure cognitive function in diverse populations and is sensitive for assessing developmental changes in children. Although CANTAB has been used in several countries, its applicability in a Mexican child population is unknown. This study examined developmental trends on CANTAB in a large sample of urban Mexico City youth and tested the hypothesis that their performance would be similar to a large US normative sample.Method: As part of a birth cohort, Early Life Exposures in Mexico to Environmental Toxicants, 826 children, ages 5–15 years, completed CANTAB. Subtests measured planning (Stockings of Cambridge; SOC), short-term memory (Delayed Matching to Sample; DMS), sustained attention (Rapid Visual Information Processing; RVP), ability to match visual stimuli (Match to Sample Visual Search; MTS), flexibility (Intra-extra Dimensional Set Shift; IED), and response inhibition (Stop Signal Task; SST). Determinants of performance on the CANTAB, including age, maternal/child IQ, and sex, were analyzed using Spearman correlation and Welch t tests. Equivalence testing compared performance with existing norms.Results: Performance improved with age on all measures. Child IQ was mildly associated with measures of memory and attention but not executive functioning, consistent with US norms. Maternal IQ was not associated with any outcomes, and males performed better on IED. Mexican norms were comparable to US norms on almost all outcomes, with the exception of a short-term visual recognition memory task (DMS).Conclusions: This study provides the largest normative data for CANTAB performance in a community sample of Mexican youth. Findings demonstrate the expected maturational effects of executive function, specifically in cognitive shifting and inhibition. Levels of executive function performance demonstrated by a Mexican sample were consistent with normative values reported in US youth. These findings, as well as expected associations with child IQ, indicate high applicability of CANTAB for Mexican youth in neurobehavioral studies.

A Dissociation of the Acute Effects of Bupropion on Positive Emotional Processing and Reward Processing in Healthy Volunteers.

Background: Previous research indicates that antidepressants can restore the balance between negative and positive emotional processing early in treatment, indicating a role of this effect in later mood improvement. However, less is known about the effect of antidepressants on reward processing despite the potential relevance to the treatment of anhedonia. In this study, we investigated the effects of an acute dose of the atypical antidepressant (dual dopamine and noradrenaline reuptake inhibitor) bupropion on behavioral measures of emotional and reward processing in healthy volunteers.Methods: Forty healthy participants were randomly allocated to double-blind intervention with either an acute dose of bupropion or placebo prior to performing the Emotional Test Battery (ETB) and a probabilistic instrumental learning task.Results: Acute bupropion significantly increased the recognition of ambiguous faces as happy, decreased response bias toward sad faces and reduced attentional vigilance for fearful faces compared to placebo. Bupropion also reduced negative bias compared to placebo in the emotional recognition memory task (EMEM). There was no evidence that bupropion enhanced reward processing or learning. Instead, bupropion was associated with reduced likelihood to choose high-probability wins and increased score on a subjective measure of anhedonia.Conclusions: Whilst acute bupropion decreases negative and increases positive emotional processing, it has an adverse effect on reward processing. There seems to be a dissociation of the acute effects of bupropion on positive emotional processing and reward processing, which may have clinical implications for anhedonia early in treatment.

Chronic Treatment with Combined Chemotherapeutic Agents Affects Hippocampal Micromorphometry and Function in Mice, Independently of Neuroinflammation.

Chemotherapeutic agents induce long-term side effects, including cognitive impairment and mood disorders, particularly in breast cancer survivors who have undergone chemotherapy. However, the precise mechanisms underpinning chemotherapy-induced hippocampal dysfunction remain unknown. In this study, we investigated the detrimental effects of chronic treatment with a combination of adriamycin and cyclophosphamide (AC) on the neuronal architecture and functions of the hippocampi of female C57BL/6 mice. After chronic AC administration, mice showed memory impairment (measured using a novel object recognition memory task) and depression-like behavior (measured using the tail suspension test and forced swim test). According to Golgi staining, chronic AC treatment significantly reduced the total dendritic length, ramification, and complexity as well as spine density and maturation in hippocampal neurons in a sub-region-specific manner. Additionally, the AC combination significantly reduced adult neurogenesis, the extent of the vascular network, and the levels of hippocampal angiogenesis-related factors. However, chronic AC treatment did not increase the levels of inflammation-related signals (microglial or astrocytic distribution, or the levels of pro-inflammatory cytokines or M1/M2 macrophage markers). Thus, chronic AC treatment changed the neuronal architecture of the adult hippocampus, possibly by reducing neurogenesis and the extent of the vasculature, independently of neuroinflammation. Such detrimental changes in micromorphometric parameters may explain the hippocampal dysfunction observed after cancer chemotherapy.

Progesterone receptor expression in cajal-retzius cells of the developing rat dentate gyrus: Potential role in hippocampus-dependent memory.

The development of medial temporal lobe circuits is critical for subsequent learning and memory functions later in life. The present study reports the expression of progesterone receptor (PR), a powerful transcription factor of the nuclear steroid receptor superfamily, in Cajal-Retzius cells of the molecular layer of the dentate gyrus of rats. PR was transiently expressed from the day of birth through postnatal day 21, but was absent thereafter. Although PR immunoreactive (PR-ir) cells did not clearly express typical markers of mature neurons, they possessed an ultrastructural morphology consistent with neurons. PRir cells did not express markers for GABAergic neurons, neuronal precursor cells, nor radial glia. However, virtually all PR cells co-expressed the calcium binding protein, calretinin, and the glycoprotein, reelin, both reliable markers for Cajal-Retzius neurons, a transient population of developmentally critical pioneer neurons that guide synaptogenesis of perforant path afferents and histogenesis of the dentate gyrus. Indeed, inhibition of PR activity during the first two weeks of life impaired adult performance on both the novel object recognition and object placement memory tasks, two behavioral tasks hypothesized to describe facets of episodic-like memory in rodents. These findings suggest that PR plays an unexplored and important role in the development of hippocampal circuitry and adult memory function.

Delay-Dependent Impairments in Memory and Motor Functions After Acute Methadone Overdose in Rats.

Methadone is used as a substitution drug for the treatment of opioid dependence and chronic pain. Despite its widespread use and availability, there is a serious concern with respect to the relative safety of methadone. The purpose of this study was to characterize how acute methadone overdose affects the cognitive and motor performance of naïve healthy rats. The methadone overdose was induced by administering an acute toxic dose of methadone (15 mg/kg; ip; the equivalent dose of 80% of LD50) to adolescent rats. Resuscitation using a ventilator pump along with a single dose of naloxone (2 mg/kg; ip) was administered following the occurrence of apnea. The animals which were successfully resuscitated divided randomly into three apnea groups that evaluated either on day 1, 5, or 10 post-resuscitation (M/N-Day 1, M/N-Day 5, and M/N-Day 10 groups) in the Y-maze and novel object memory recognition tasks as well as pole and rotarod tests. The data revealed that a single toxic dose of methadone had an adverse effect on spontaneous behavior. In addition, Recognition memory impairment was observed in the M/N-Day 1, 5, and 10 groups after methadone-induced apnea. Further, descending time in the M/N-Day 5 group increased significantly in comparison with its respective Saline control group. The overall results indicate that acute methadone-overdose-induced apnea produced delay-dependent cognitive and motor impairment. We suggest that methadone poisoning should be considered as a possible cause of delayed neurological disorders, which might be transient, in some types of memory or motor performance in naïve healthy rats.