Classic and recent advances in understanding amnesia

Familiarity deficits in aMCI under conditions that minimize the influence of recollection

OBJECTIVE

Familiarity, the sense of knowing without recalling specific details, plays a critical role in memory processing and is mediated by the perirhinal cortex (PRC), a brain region that is critical for differentiating objects with high feature overlap, and is affected first by amnestic mild cognitive impairment (aMCI). Investigating familiarity in aMCI is crucial for insights into early diagnostic markers of cognitive impairment.

METHOD

We conducted two studies probing familiarity in aMCI. The first study employed a response deadline procedure (RDP) where participants were presented with pictures of objects and then completed an item recognition test under two deadlines: a long deadline of 5000 ms, indexing recollection, and a short deadline of 1200ms, indexing familiarity. The second study utilized a frequency judgment (FJ) task in which participants saw pictures of highly similar objects a variable number of times, and then were asked how many times each object was presented. Their frequency judgments were correlated with the actual presentation frequencies as a measure of familiarity.

RESULTS

In the RDP, individuals with aMCI had significantly lower recognition accuracy than healthy counterparts, in the long and short deadline, indicating impaired recollection and familiarity. In the FJ task, individuals with aMCI had significantly lower frequency judgment correlations, indicating impaired familiarity.

DISCUSSION

These results highlight the importance of minimizing the role of recollection when aiming to understand familiarity deficits and underscore the potential of familiarity as an early diagnostic marker of cognitive decline.

Memory States From Almost Nothing: Representing and Computing in a Nonassociative Algebra

This letter presents a nonassociative algebraic framework for the representation and computation of information items in high-dimensional space. This framework is consistent with the principles of spatial computing and with the empirical findings in cognitive science about memory. Computations are performed through a process of multiplication-like binding and nonassociative interference-like bundling. Models that rely on associative bundling typically lose order information, which necessitates the use of auxiliary order structures, such as position markers, to represent sequential information that is important for cognitive tasks. In contrast, the nonassociative bundling proposed allows the construction of sparse representations of arbitrarily long sequences that maintain their temporal structure across arbitrary lengths. In this operation, noise is a constituent element of the representation of order information rather than a means of obscuring it. The nonassociative nature of the proposed framework results in the representation of a single sequence by two distinct states. The L-state, generated through left-associative bundling, continuously updates and emphasizes a recency effect, while the R-state, formed through right-associative bundling, encodes finite sequences or chunks, capturing a primacy effect. The construction of these states may be associated with activity in the prefrontal cortex in relation to short-term memory and hippocampal encoding in long-term memory, respectively. The accuracy of retrieval is contingent on a decision-making process that is based on the mutual information between the memory states and the cue. The model is able to replicate the serial position curve, which reflects the empirical recency and primacy effects observed in cognitive experiments.

Sobrerol Improves Memory Impairment in the Scopolamine-Induced Amnesia Mouse Model

Memory impairment is a defining characteristic of Alzheimer's disease (AD), with amnesia often appearing as its earliest symptom. Given the multifactorial nature of AD pathogenesis, this study investigates the multi-target therapeutic potential of sobrerol (coded as NRM-331) in a scopolamine-induced amnesia mouse model, focusing specifically on its effects in ameliorating memory deficits and enhancing neuronal plasticity. Sixty male C57BL/6NCrljOri mice were divided into six groups (10 mice/group): vehicle control (CTL, saline), scopolamine (SPA, 10 mg/kg/day), Aricept (APT, 2 mg/kg/day), and three treatment groups receiving NRM-331 at doses of 40, 80, and 100 mg/kg/day. Several behavioral tests were conducted, including the Y-maze test, passive avoidance test, and Morris water maze test. Additionally, biochemical assays were performed in serum (to measure Aß 1-40 and Aß 1-42) and in the brain (to assess ACh and AChE levels), along with histopathological examination of the brain using Nissl staining and p-tau IHC. No significant change was observed in the Y-maze test or the acquisition trial of the passive avoidance test. However, improvements were noted in the retention trial of the passive avoidance test and the Morris water maze test (including escape latency, swim distance, and number of platform crossed) for the NRM-331 groups compared to the SPA group. Serum levels of Aß 1-40 and Aß 1-42 decreased in the NRM-331 groups compared to the SPA group. In the brain, levels of ACh significantly increased, while AChE levels significantly decreased compared to the SPA group. The number of neuronal cells improved in the CA1, CA3, and DG regions of the hippocampus, as indicated by Nissl staining. A significant reduction in p-tau accumulation was also observed in the NRM-331 groups. In conclusion, NRM-331 demonstrated an anti-amnesic effect by enhancing hippocampal cholinergic signaling, alongside exhibiting anti-tau and anti-Aβ synthesis properties. These therapeutic effects suggest that NRM-331 significantly mitigates memory impairment induced by SPA through a neuroprotective mechanism.

Amnestic syndrome in the course of seronegative limbic encephalitis complicated by drug-resistant epilepsy: a case report

We present the case of a 35-year-old female patient admitted to the hospital with symptoms of rapidly increasing disturbances of consciousness and fever for 48 hours. A lumbar puncture, bacteriological and virological examinations, and initial imaging studies did not show abnormalities. Brain magnetic resonance imaging (MRI), repeated several times, showed hyperintense confluent lesions in both temporal lobes and atrophy of both hippocampi. General examination, cerebrospinal fluid culture, the panel of antineuronal antibodies, and tumor markers remained negative on subsequent repeats. Despite several laboratory and imaging studies, the etiology of the disease could not be established, infections were excluded, and no autoantibodies were found. A diagnosis of probable limbic encephalitis, amnestic syndrome resulting from organic brain damage, and drug-resistant epilepsy was made. The patient, with limbic encephalitis complicated by drug-resistant status epilepticus, was treated with cycles of immunoglobulin and subsequent plasmapheresis. She was then transferred to the Department of Psychiatry for diagnosis and treatment of intermittent psychotic disorders. During hospitalization, the patient was observed to have multiple epileptic seizures with temporal and frontal morphology, amnestic syndrome with confabulations, and periodic psychotic disorders with the occurrence of visual hallucinations. Antiepileptic treatment was escalated by including cenobamate in increasing doses. To control the mental disorders, duloxetine, tiapride, and cognitive function exercises were introduced. There was a slight improvement in memory, a cessation of confabulations, and an emergence of the patient's criticism of the symptoms presented. The psychotic symptoms subsided, and the number of epileptic seizures decreased. The described case portrays a unique co-occurrence of disease symptoms that are difficult to treat. It shows the therapeutic difficulties that can occur in patients with suspected autoimmune encephalitis. Furthermore, it shows the need for multispecialty care of a patient with psychotic symptoms in the course of epilepsy accompanied by amnestic syndrome.

Metabolomics study to reveal cognitive improvement with treatment of Scrophularia buergeriana

Population aging around the world is rapidly progressing; as a result, cognitive decline developing into dementia is becoming a social problem. There is no drug that can cure dementia, and though drugs that alleviate the symptoms of dementia have been developed, they also have side effects. Therefore, we conducted a study on improving cognitive function using natural products that have secured safety. We confirmed the effect of an extract of Scrophularia buergeriana on scopolamine-induced cognitive impairment through mouse behavioral experiments, and we observed metabolic changes in the cortex and hippocampus via brain tissue dissection after the behavioral experiment. Mitigating effects of S. buergeriana on cognitive impairment caused by scopolamine were observed in passive avoidance and Morris water maze tests. A metabolic analysis revealed biomarkers related to the alleviating effect of cognitive impairment. Niacinamide, tyrosine, uridine, and valine in the cortex and GABA, choline, creatine, formate, fumarate, hypoxanthine, leucine, myo-inositol, pyroglutamate, and taurine in the hippocampus were identified as biomarker candidates for recovering cognitive impairment. In addition to behavioral experiments, this metabolomics study using specific regions of the brain may be helpful in understanding the effects of cognitive improvement.

Complex visual discrimination is impaired after right, but not left, anterior temporal lobectomy

The prevailing view in human cognitive neuroscience associates the medial temporal lobes (MTLs) with declarative memory. Compelling experimental evidence has, however, demonstrated that these regions are specialized according to the representations processed, irrespective of the cognitive domain assessed. This account was supported by the study of patients with bilateral medial temporal amnesia, who exhibit impairments in perceptual tasks involving complex visual stimuli. Yet, little is known regarding the impact of unilateral MTL damage on complex visual abilities. To address this issue, we administered a visual matching task to 20 patients who underwent left (N = 12) or right (N = 8) anterior temporal lobectomy for drug-resistant epilepsy and to 38 healthy controls. Presentation viewpoint was manipulated to increase feature ambiguity, as this is critical to reveal impairments in perceptual tasks. Similar to control participants, patients with left-sided damage succeeded in all task conditions. In contrast, patients with right-sided damage had decreased accuracy compared with that of the other two groups, as well as increased response time. Notably, the accuracy of those with right-sided damage did not exceed chance level when feature ambiguity was high (i.e., when stimuli were presented from different viewpoints) for the most complex classes of stimuli (i.e., scenes and buildings, compared with single objects). The pattern reported in bilateral patients in previous studies was therefore reproduced in patients with right, but not left, resection. These results suggest that the complex visual-representation functions supported by the MTL are right-lateralized, and raise the question as to how the representational account of these regions applies to representations supported by left MTL regions.

Genistein suppresses microglial activation and inhibits apoptosis in different brain regions of hypoxia-exposed mice model of amnesia

Genistein (GE) or 4',5,7-trihydroxyflavone, a plant derived isoflavone, is a biologically active compound having several beneficial properties. Studies showed that GE possesses anti-neoplastic, anti-tumor, anti-helminthic, anti-oxidant, and anti-inflammatory activities. Herein, we investigated the neuroprotective effects of GE in a mouse model of hypoxia-induced amnesia. Mice were exposed to hypoxic conditions (10% O2) in a designated hypoxia chamber and co-treated with GE (10, 20, or 30 mg/kg) for 4 weeks. Following this, behavioral tests were performed to evaluate memory performance. We assessed microglial activation in the hippocampus, amygdala, and pre-frontal cortex (PFC) regions by evaluating the Iba-1 and GFAP transcript levels, and MIP-1β, Cox-2, and IL6 protein levels. Apoptosis was assessed by evaluating Bax, BAD, and Bcl-2 mRNA levels, and caspase-3 activity. To uncover the underlying molecular mechanism, we evaluated the levels of Nrf2, HO-1, and NQO1 in different brain regions of mice from all groups. Results showed that hypoxia-exposed mice have reduced performance in the behavioral tests and GE treatment enhanced the memory performance in hypoxia-exposed mice. Moreover, hypoxia-exposed mice showed increased expression of microglial activation markers and enhanced apoptosis in the hippocampus, amygdala, and PFC. GE treatment suppressed microglial activation and prevented apoptosis in the brain of hypoxia-exposed mice. Furthermore, hypoxia-exposure reduced the expression of Nrf2, NQO1, and HO-1 while GE treatment ameliorated this decrease in different regions of hypoxia-exposed mice brain. In conclusion, GE prevents cognitive dysfunction by suppressing microglial activation and inhibiting apoptosis in the hypoxia-exposed mice brain.

Intact high-resolution working memory binding in a patient with developmental amnesia and selective hippocampal damage

Debate continues regarding the possible role of the hippocampus across short-term and working memory tasks. The current study examined the possibility of a hippocampal contribution to precise, high-resolution cognition and conjunctive memory. We administered visual working memory tasks featuring a continuous response component to a well-established developmental amnesic patient with relatively selective bilateral hippocampal damage (Jon) and healthy controls. The patient was able to produce highly accurate response judgments regarding conjunctions of color and orientation or color and location, using simultaneous or sequential presentation of stimuli, with no evidence of any impairment in working memory binding, categorical accuracy, or continuous precision. These findings indicate that hippocampal damage does not necessarily lead to deficits in high-resolution cognitive performance, even when the damage is severe and bilateral.

Misconceptions About Traumatic Brain Injuries in Five Sub-Saharan African Countries

Background Traumatic Brain Injury (TBI) remains a significant problem in certain regions of the world but receives little attention despite its enormous burden. This discrepancy could consequently lead to various misconceptions among the general public. This study evaluated misconceptions about TBI in five African countries. Methods Data for this cross-sectional study were collected using the Common Misconception about Traumatic Brain Injury (CM-TBI) questionnaire, which was electronically disseminated from January 16 to February 6, 2021. Associations between the percentage of correct answers and independent variables (i.e., sociodemographic characteristics and experience with TBI) were evaluated with the ANOVA test. Additionally, answers to the question items were compared against independent variables using the Chi-Square test. A P-value <0.05 was considered statistically significant. Results A total of 817 adults, 50.2% female (n=410), aged 24.3 ± 4.3 years, and majoritarily urban dwellers (94.6%, n=773) responded to the survey. They had received tertiary education (79.2%, n=647) and were from Nigeria (77.7%, n=635). Respondents had few misconceptions (mean correct answers=71.7%, 95% CI=71.0-72.4%) and the amnesia domain had the highest level of misconception (39.3%, 95% CI=37.7-40.8%). Surveyees whose friends had TBI were more knowledgeable about TBI (mean score difference=4.1%, 95% CI=1.2-6.9, P=0.01). Additionally, surveyees whose family members had experienced TBI had a better understanding of brain damage (mean score difference=5.7%, 95% CI=2.1-9.2%, P=0.002) and recovery (mean score difference=4.3%, 95% CI=0.40-8.2%, P=0.03). Conclusion This study identified some misconceptions about TBI among young adult Africans. This at-risk population should benefit from targeted education strategies to prevent TBI and reduce TBI patients' stigmatization in Africa.

Analysing Curcuma caesia fractions and essential oil for neuroprotective potential against anxiety, depression, and amnesia

Scientific pieces of evidence support the pharmacological activity of Curcuma caesia for its antidepressant, analgesic, anticonvulsant and antioxidant effect. Here, we evaluate the bioactivity of essential oil and the various polarity-based solvent partitioned fractions obtained from Curcuma caesia for anti-amnesia, anxiolytic and antidepressant activities using Elevated plus maze and Morris water maze models. The cold maceration technique using methanol was adopted for extraction from dried powdered rhizomes and essential oil was extracted by hydrodistillation method. Partitioning of the methanolic extract based on solvent polarity by hexane, ethyl acetate, and methanol was continued, followed by column chromatography of the ethyl acetate fraction. Suspensions were prepared for fractions (dissolved in distilled water) and essential oil (dissolved in tween 20) at 200 mg/kg and 400 mg/kg after acute toxicity study and were orally administered to Wistar albino female rats after the orientation of hypoxia by sodium nitrite (50 mg/kg) and amnesia by scopolamine (1 mg/kg). Behavioural observations, biochemical and histopathological examinations were carried out for all the treated groups. Diazepam (12 mg/kg) and galantamine (3 mg/kg) were used as standard drugs for this study against hypoxia and amnesia. Data acquired from behavioural, biochemical (acetylcholinesterase, myeloperoxidase, superoxide dismutase, reduced glutathione, catalase) and histopathological studies have illustrated that fraction II acquires highly significant memory-enhancing, anxiolytic and antidepressant effects. Rest fractions (I and III) and essential oil showed moderate efficacy. In prospects, identification of active molecules from the most active fraction (fraction II) and further studies on a molecular basis would substantiate its specific mechanism of neuroprotective action.

Genistein Prevents Hypoxia-Induced Cognitive Dysfunctions by Ameliorating Oxidative Stress and Inflammation in the Hippocampus

Genistein (GE), a plant-derived isoflavone, is a polyphenolic non-steroidal compound. Studies showed that GE possesses anti-cancer, anti-inflammatory, anti-microbial, anti-oxidant, and anti-apoptotic activities. However, the neuroprotective role of GE in amnesia has not been studied. This study aimed to evaluate the anti-amnesic potential of GE in a mice model of hypoxia-induced amnesia and to understand the underlying mechanism. Mice were exposed to hypoxia (10% O2) and administered vehicle or GE (10, 20, 30 mg/kg) orally for 28 days. Thereafter, Morris water maze (MWM), novel object recognition (NOR), and passive avoidance task (PAT) were performed to evaluate cognitive behavior. Next, we performed biochemical tests and gene expression analysis to uncover the mechanism underlying GE mode of action. Our results showed that GE-treatment ameliorated hypoxia-induced cognitive dysfunctions in mice. Further, GE-treatment suppressed the oxidative stress in the hippocampus of amnesic mice as evidenced by reduced lipid peroxidation, reduced nitrite and ROS levels, and increased levels of reduced glutathione (GSH) and increased total antioxidant capacity. GE treatment reduced the expression of pro-inflammatory cytokines TNFα, IL1β, IL6, and MCP-1 and increased the expression of anti-inflammatory cytokine IL10 in the hippocampus of amnesic mice. Finally, GE treatment enhanced the expression of neuroprotective genes including BDNF, CREB, CBP, and IGF1 in the hippocampus of amnesic mice. Altogether, our results showed that GE treatment prevents hypoxia-induced cognitive dysfunction in mice by reducing oxidative stress and suppressing neuroinflammation while increasing the expression of neuroprotective genes in the hippocampus.

Evaluation of neuroprotective and anti-amnesic effects of Elaeagnus umbellata Thunb. On scopolamine-induced memory impairment in mice

BACKGROUND

Elaeagnus umbellata is abundantly found in Himalayan regions of Pakistan which is traditionally used to treat various health disorders. However, the experimental evidence supporting the anti-amnesic effect is limited. Therefore the study was aimed to evaluate the prospective beneficial effect of E. umbellata on learning and memory in mice.

OBJECTIVES

To assess neuroprotective and anti-amnesic effects of E. umbellata fruit extracts and isolated compounds on the central nervous system.

METHODS

Major phytochemical groups present in methanolic extract of E. umbellata were qualitatively determined. The total phenolic and flavonoid contents were also determined in extract/fractions of E. umbellata. On the basis of in vitro promising anticholinesterases (AChE & BChE) and antioxidant activities observed for CHF. Ext and isolated compound-I (Chlorogenic acid = CGA), they were further evaluated for learning and memory in normal and scopolamine-induced cognitive impairment in mice using memory behavioral tests such as the Y maze and Novel object recognition using standard procedures. The test sample were further assessed for in vivo anticholinesterases (AChE & BChE) and DPPH free radical scavenging activities in mice brain sample and finally validated by molecular docking study using GOLD software.

RESULTS

The extract/fractions and isolated compounds were tested for their anticholinesterase and antioxidant potentials. The CHF. Ext and CGA showed maximum % inhibition of tested cholinesterases and free radicals. The CHF. Ext and CGA reversed the effects of scopolamine in mice. The CHF. Ext and CGA significantly increased the alternate arm returns and % spontaneous alteration performance while escape latency times (second) significantly decreased in Y maze test. The CHF. Ext and CGA significantly increased the time spent with novel object and also increased the discrimination index in the Novel object recognition test. Furthermore, molecular docking was used to validate the mechanism of cholinesterases inhibition of isolated compounds.

CONCLUSION

The data obtained from behavioral and biochemical studies (AChE/BChE and DPPH/ABTS inhibition) have shown that E. umbellata possessed significant memory enhancing potency. These results suggest that E. umbellata extract possess potential antiamnesic effects and amongst the isolated compounds, compound I could be more effective anti-amnesic therapeutics. However, further studies are needed to identify the exact mechanism of action.

A review of hippocampal activation in post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is often characterized by deficits in memory encoding and retrieval and aberrant fear and extinction learning. The hippocampus plays a critical role in memory and contextual processing and has been implicated in intrinsic functional connectivity networks involved in self-referential thought and memory-related processes. This review focuses on hippocampal activation findings during memory and fear and extinction learning tasks, as well as resting state hippocampal connectivity in individuals with PTSD. A preponderance of functional neuroimaging studies to date, using memory, fear learning, and extinction tasks, report decreased or "controls comparable" hippocampal activation in individuals with PTSD, which is usually associated with poorer performance on the task imaged. Existing evidence thus raises the possibility that greater hippocampal recruitment in PTSD participants may be required for similar performance levels. Studies of resting state functional connectivity in PTSD predominantly report reduced within-network connectivity in the default mode network (DMN), as well as greater coupling between the DMN and salience network (SN) via the hippocampus. Together, these findings suggest that deficient hippocampal activation in PTSD may be associated with poorer performance during memory, extinction recall, and fear renewal tasks. Furthermore, studies of resting state connectivity implicate the hippocampus in decreased within-network DMN connectivity and greater coupling with SN regions characteristic of PTSD.