Imaging evidence for disturbances in multiple learning and memory systems in persons with autism spectrum disorders

Abstract

ASD Autism spectrum disorders MNS Mirror neuron system STS Superior temporal sulcus AIM The aim of this article is to review neuroimaging studies of autism spectrum disorders (ASD) that examine declarative, socio-emotional, and procedural learning and memory systems.METHOD We conducted a search of PubMed from 1996 to 2010 using the terms 'autism,' 'learning,' 'memory,' and 'neuroimaging.' We limited our review to studies correlating learning and memory function with neuroimaging features of the brain. RESULTSThe early literature supports the following preliminary hypotheses: (1) abnormalities of hippocampal subregions may contribute to autistic deficits in episodic and relational memory; (2) disturbances to an amygdala-based network (which may include the fusiform gyrus, superior temporal cortex, and mirror neuron system) may contribute to autistic deficits in socio-emotional learning and memory; and (3) abnormalities of the striatum may contribute to developmental dyspraxia in individuals with ASD.INTERPRETATION Characterizing the disturbances to learning and memory systems in ASD can inform our understanding of the neural bases of autistic behaviors and the phenotypic heterogeneity of ASD.In 1943, Leo Kanner 1 published his seminal manuscript describing a group of children with a 'powerful desire for aloneness and sameness.' The key themes identified by Kanner have since been refined into a set of three nosological criteria that serve as the criterion standard for diagnosing autism spectrum disorders (ASD): disturbances in (1) social interaction, (2) communication, and (3) behavioral flexibility. How these different phenomenological criteria 'map' onto the brain has been a topic of intense investigation in recent years, with over 300 neuroimaging studies of ASD published in the past three decades.Although the neural bases of the individual features of the autistic triad have yet to be clearly defined, neuroimaging studies have provided key insights into the brain disturbances present in individuals with ASD. Perhaps the most important discovery has been a trajectory of early brain overgrowth within the first years of life followed by premature growth arrest.2 This aberrant growth occurs at a critical time in human brain development, during which synaptogenesis, neuronal growth and differentiation, and myelination establish networks of local and long-range connections that are essential for normal cognitive and behavioral development. Neuroimaging studies have also identified several neural systems of interest that may be associated with certain autistic behaviors. Deficits in certain social behaviors, for example, have been associated in some studies with abnormalities of the amygdala, mirror neuron system (MNS), and superior temporal gyrus, whereas stereotyped repetitive behaviors have been associated with abnormalities of the striatum. 3,4 Neuroimaging studies of ASD, however, face a number of limitations. Abnormalities of brain function are known to be present in early infancy in ASD, long before most imagi...

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“…Thus far, neuroimaging studies have not consistently reported difference in the overall volume of hippocampus between ASD and control groups [35, 39]. However, other studies have indicated that declarative memory in ASD patients is characterized by selective impairment in both encoding and retrieving of episodic memory, which is relational and contextual.…”

“…However, other studies have indicated that declarative memory in ASD patients is characterized by selective impairment in both encoding and retrieving of episodic memory, which is relational and contextual. In contrast, semantic memory, which is factual and item-based, is relatively preserved [39]. Some individuals with ASD even exhibit superior memory that depends on repetition and familiarity, but have difficulties with memory that uses relation and context.…”

“…Some individuals with ASD even exhibit superior memory that depends on repetition and familiarity, but have difficulties with memory that uses relation and context. It has been hypothesized that these impairments may be due to alterations in hippocampal function and/or connectivity [39]. For example, recent studies reported that male carriers of the FMR1 premutation, who are at increased risk of developing ASD, showed altered hippocampal-prefrontal connectivity during memory encoding [40] and reduced hippocampal activation during memory recall [41].…”

Mesial temporal lobe and memory function in autism spectrum disorder: An exploration of volumetric findings

“…It may be that more refined measures that assess neural connectivity and networks such as fMRI and diffusion tensor imaging (DTI) will better clarify the neurobiological basis of memory impairment in autism. A review of the literature on memory in ASD by Goh and Peterson (2012) reveals that the bulk of the existing research in this involves structural imaging rather than functional imaging, so there is an absence of such research to address the neural connectivity of memory in ASD. Future studies investigating the structure and functional neuroimaging of neural pathways in memory regions may provide insight regarding abnormalities that contribute to memory and learning impairments in this population.…”

Selective Modulators of α₅-Containing GABA_A Receptors and their Therapeutic Significance

“…As with Down syndrome, children diagnosed with autism spectrum disorder (ASD) may also experience impairments in hippocampal-dependent learning and memory [76]. However, unlike Down syndrome, it is the excessive neural activity, leading to excitatory/inhibitory imbalance in the brain, that has been implicated with the neuropathological characteristics of ASD [21,77].…”