Memory in Autism: Review and Synthesis

doi:10.1016/S0010-9452(08)70881-5

Cortex

Volume 39, Issues 4–5, 2003, Pages 1129-1138

https://doi.org/10.1016/S0010-9452(08)70881-5 Get rights and content

Abstract

Much research about memory in autism concerns the hypothesis that autism is similar to adult-onset amnesia. Initial support for the hypothesis came from post-mortem studies of individuals with autism showing abnormalities in the hippocampus and related brain structures, as well as behavioral studies finding contrasts between intact cued recall and impaired free recall and recognition in autism. The hypothesis was later brought into question by the finding of intact performance in individuals with autism on explicit memory tasks typically impaired in adult-onset amnesia. The present paper proposes a possible reconciliation of these contradictory findings, suggesting that there is selective damage to the limbic-prefrontal episodic memory system, sparing the limbic-only perceptual representation system, and the semantic memory system. This view is consistent with other evidence for early selective damage to other systems involving cooperation between the limbic system and the medial prefrontal cortex in autism.

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Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder that impacts a variety of cognitive and behavioral domains. While a genetic component of ASD has been well-established, none of the numerous syndromic genes identified in humans accounts for more than 1% of the clinical patients. Due to this large number of target genes, numerous mouse models of the disorder have been generated. However, the focus on distinct brain circuits, behavioral phenotypes and diverse experimental approaches has made it difficult to synthesize the overwhelming number of model animal studies into concrete throughlines that connect the data across levels of investigation. Here we chose to focus on one circuit, the hippocampus, and one hypothesis, a shift in excitatory/inhibitory balance, to examine, from the level of the tripartite synapse up to the level of in vivo circuit activity, the key commonalities across disparate models that can illustrate a path towards a better mechanistic understanding of ASD’s impact on hippocampal circuit function.
Neuroprotective effect of the standardised extract of Bacopa monnieri (BacoMind) in valproic acid model of autism spectrum disorder in rats
2022, Journal of Ethnopharmacology
Bacopa monnieri (BM) is commonly employed in the Indian traditional system of medicines, i.e. Ayurveda as a memory booster, antioxidant, anti-inflammatory, antipyretic, analgesic, sedative and anti-epileptic for decades.
To evaluate the neuroprotective effect of Bacopa monnieri (BM) in experimental model of autism spectrum disorder (ASD) in Wistar rats and explore its mechanism of action.
BacoMind, was evaluated for its neuroprotective effect in valproic acid (VPA) model of ASD. For in-vivo study, the pregnant female Wistar rats were divided in two groups; normal control (NC) and VPA group who received single dose of normal saline (0.9%) or 600 mg/kg dose of VPA respectively on gestation day (G.D) 12.5. After the birth, all pups were segregated according to the sex. All the male pups from the dams were divided into six groups: Group 1 (NC, treated with only 0.9% normal saline, group 2 (VPA, treated 600 mg/kg on G.D12.5 and normal saline from post natal day (PND) 23 to 43), group 3 (risperidone 2.5 mg/kg, PND 23 to 43) and groups 4, 5 and 6 (BM 20, 40, 80 mg/kg, PND 23 to 43). All experimental groups were subjected to batteries of behavior parameters (three chamber sociability test, Morris Water Maze, elevated plus maze, open field and rota rod test), biochemical parameters such as oxidative stress (GSH, SOD, Catalase, MDA), inflammatory cytokines (Il-1β, IL-6, IL-10, TNF-α), histopathological examination (cresyl violet staining) of hippocampus (HC) and prefrontal cortex (PFC) regions. Further, the mRNA as well as protein expression of AMPA receptor was evaluated using RT-PCR and western blot respectively to study the mechanism of neuroprotective effect of BM. The in-silico analysis followed evaluating the binding profile of different constituents of BacoMind with AMPA receptor.
The results of the in-vivo study indicated BM at 80 mg/kg ameliorated abnormal behavioral paradigms such as social deficits, repetitive behavior, learning and memory impairments, and motor coordination exhibited by the VPA model of ASD in rats. Furthermore, BM was found to have a significant anti-oxidant (increasing GSH, SOD, and catalase and decreasing MDA levels) and anti-inflammatory properties (decreasing IL-1β, 6, TNF- α). The histopathological score was also found to be significantly improved by BM in a dose dependent manner in both HC and PFC. In addition to this, the up-regulated mRNA as well as protein expression of AMPA receptor was significantly reduced by 80 mg/kg dose of BM in both HC and PFC. Further, the in-silico analysis of different constituents of BacoMind with AMPA receptor demonstrated that luteolin and apigenin showed good binding to both the competitive antagonist binding site, non-competitive antagonist binding site and allosteric modulator site while Bacosaponin C showed good binding to the non-competitive antagonist binding site.
The present study concluded that BM can be a potential candidate for ameliorating the ASD symptoms in rats and acts via modulating the up-regulated AMPA receptor expression.
Should context hold a special place in hippocampal memory?
2021, Psychology of Learning and Motivation - Advances in Research and Theory
Episodic memory research has often focused on the role of the hippocampus in binding items to contexts, highlighting a privileged, or special, role for context in relational memory representations. In the present review, we ask whether context is indeed special to relational memory and hippocampal processing, or whether the hippocampus is engaged in binding all types of relational information, not limited to just context. We survey the evidence demonstrating the necessity for hippocampal processing in item-context binding and context-guided behavior. Then, we discuss evidence that the hippocampus is critical for relational binding beyond item-context, including item-item relations, as well as high-resolution single item memory, and pattern separation. This view is crucial to understanding the role of the hippocampus, not just in episodic memory, but also in guiding in-the-moment processing beyond the constraints of a context-centric view of hippocampal function. We argue that, while the hippocampus is indeed critical for item-context binding, the hippocampus is not limited by context and that context is just one of the many relations the hippocampus can bind and use for the organization of relational information, all in service of flexible cognition. We conclude that while the hippocampus is special to context, context is not special to the hippocampus.
Enhancing cognition through pharmacological and environmental interventions: Examples from preclinical models of neurodevelopmental disorders
2020, Neuroscience and Biobehavioral Reviews
In this review we discuss the role of environmental and pharmacological treatments to enhance cognition with special regards to neurodevelopmental related disorders and aging. How the environment influences brain structure and function, and the interactions between rearing conditions and gene expression, are fundamental questions that are still poorly understood. We propose a model that can explain some of the discrepancies in findings for effects of environmental enrichment on outcome measures. Evidence of a direct causal correlation of nootropics and treatments that enhanced cognition also will be presented, and possible molecular mechanisms that include neurotrophin signaling and downstream pathways underlying these processes are discussed. Finally we review recent findings achieved with a wide set of behavioral and cognitive tasks that have translational validity to humans, and should be useful for future work on devising appropriate therapies. As will be discussed, the collective findings suggest that a combinational therapeutic approach of environmental enrichment and nootropics could be particularly successful for improving learning and memory in both developmental disorders and normal aging.
Compensatory Hippocampal Recruitment Supports Preserved Episodic Memory in Autism Spectrum Disorder
2020, Biological Psychiatry: Cognitive Neuroscience and Neuroimaging
The degree to which individuals with autism spectrum disorder (ASD) evidence impairments in episodic memory relative to their typically developing (TD) counterparts remains unclear. According to a prominent view, ASD is associated with deficits in encoding associations between items and recollecting precise context details. Here, we evaluated behavioral and neural evidence for this impaired relational binding hypothesis using a task involving relational encoding and recollection during functional magnetic resonance imaging.
Adolescents and young adults (n_ASD = 47, n_TD = 60) performed the Relational and Item-Specific Encoding task during functional magnetic resonance imaging, including item and associative recognition testing. We modeled functional recruitment within the medial temporal lobes (MTLs), and connectivity between MTL and the posterior medial (PM) network thought to underlie relational memory. The impaired relational binding model would predict a behavioral deficit driven by aberrant recruitment and connectivity of MTL and the PM network.
The ASD and TD groups showed indistinguishable item and associative recognition performance. During relational encoding, the ASD group demonstrated increased hippocampal recruitment, and decreased connectivity between MTL and PM regions relative to the TD group. Within ASD, hippocampal recruitment and MTL-PM connectivity were inversely correlated.
The lack of a behavioral deficit in ASD does not support the impaired relational binding hypothesis. Instead, the current data suggest that increased recruitment of the hippocampus compensates for decreased MTL-PM connectivity to support preserved episodic memory in ASD. These findings suggest a compensatory neurodevelopmental mechanism that may support preserved cognitive domains in ASD: local hyperrecruitment may offset connectivity aberrations in individuals with ASD relative to TD subjects.
Functional brain connectivity in a rodent seizure model of autistic-like behavior
2019, Epilepsy and Behavior
Citation Excerpt :
In addition, compared with the CTL groups, rats with ELS had decreases in sleep spindle density, indicating a decrease in thalamocortical information flow. Both the hippocampus and PFC are important in learning and memory and have been implicated in the pathophysiology of ASD [33–36]. While the hippocampus stores an explicit representation of space that is used as a “cognitive map” to guide goal-based behavior [37–41], the CA1-PFC pathway is crucial for goal-directed decision-making and providing abstract representations of goals and intentions [42–45].
There is increasing evidence that Autism Spectrum Disorder (ASD) is a disorder of functional connectivity with both human and rodent studies demonstrating alterations in connectivity. Here, we hypothesized that early-life seizures (ELS) in rats would interrupt normal brain connectivity and result in autistic-like behavior (ALB).
Following 50 seizures, adult rats were tested in the social interaction and social novelty tests and then underwent qualitative and quantitative intracranial electroencephalography (EEG) monitoring in the medial prefrontal cortex (PFC) and the hippocampal subfields, CA3 and CA1.
Rats with ELS showed deficits in social interaction and novelty, and compared with control, rats had marked increases in coherence within the hippocampus (CA3-CA1) and between the hippocampus and PFC during the awake and sleep states indicating hyperconnectivity. In addition, sleep spindle density was significantly reduced in rats with ELS. There were no differences in voltage correlations and power spectral densities between the ELS and control rats in any bandwidths.
Taken together, these findings indicate that ELS can result in ALB and alter functional connectivity as measured by coherence and sleep spindle density. These findings implicate altered connectivity as a robust neural signature for ALB following ELS.

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Special IssueMemory in Autism: Review and Synthesis

Abstract

Neuropsychologia

Consciousness and Cognition

Neuroscience and Biobehavioral Reviews

Cognition

Cortex

Neurologic Clinics

Episodic memory, amnesia, and the hippocampal-anterior thalamic axis

The Behavioral and brain sciences

Visual memory processes in high-functioning individuals with autism

Journal of Autism and Developmental Disorders

Diagnostic and Statistical Manual of Mental Disorders

An animal model for childhood autism

A clinicopathological study of autism?

Brain

Mindblindedness

Histoanatomic observations of the brain in early infantile autism

Neurology

Intact and impaired memory functions in autism

Child Development

Immediate free recall in early childhood autism: Another point of behavioural similarity with the amnesic syndrome

British Journal of Psychology

Memory for recent events in autistic children

Journal of Autism and Developmental Disorders

Memory impairments and communication in relatively able autistic children

Journal of Child Psychology and Psychiatry

Memory deficits in early infantile autism: Some similarities to the amnesic syndrome

British Journal of Psychology

Episodic memory and remembering in adults with Asperger syndrome

Journal of Autism and Developmental Disorders

Are deficits in the decoding of affective cues and in mentalizing abilities independent?

Journal of Autism and Developmental Disorders

Autism: New data suggest a new hypothesis

Neurology

The clinical syndrome of early-life bilateral hippocampal sclerosis

Annals of Neurology

Special Issue
Memory in Autism: Review and Synthesis