Recent Advances and Neural Connectivity in Autism

Recent Advances and Neural Connectivity in Autism

Kiran Srivastava (Amity University, India) and Lalit Kumar Singh (Lucknow University, India)
DOI: 10.4018/978-1-5225-7004-2.ch006

Abstract

The current chapter has reviewed the functional and structural brain connectivity in children with autism spectrum disorders (ASD). Neuropathological studies of the cerebral cortex in autism indicate abnormalities of synaptic and columnar structure and of neuronal migration. The MRI morphometry in young children with autism reveals excessive volume of cerebrum or cerebral white matter or increased total brain volume. The absence of such a volume difference in adults suggests that early hyperplasia in autism is followed by a plateau during which brain growth in normal subjects catches up. The developmental course of brain connectivity and the categorization potential of different connectivity process are important topics that are investigated by different studies. Finally, several studies contribute to a better understanding of the links between cellular abnormalities in the autistic cortex (both cerebral and cerebellar) and disturbances in network connectivity.
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Introduction

Autism spectrum disorders (ASDs) are a family of neurodevelopmental syndromes with the prevalence of roughly 0.5–1.5% (Brugha, McManus, Bankart, Scott, Purdon, Smith, & Meltzer, 2011). ASDs are very common in males than in females, with a gender ratio of around 4:1 (Maenner & Durkin, 2010). ASD is a contemporary term which takes into account older concept of ‘autism’ or ‘childhood autism’, but in addition covers cases which, while sharing many of the symptoms of autism, do not cover the strict criteria for this disorder (Geschwind, 2009). ASDs are diagnosed on the basis of impairments in mainly three domains of behavior: social contact and relationships, verbal communication and repetitive, limited interests and behaviors (Robinson, Koenen, McCormick, Munir, Hallett, Happé, & Ronald, 2012). These symptoms are in attendance from early life (before 36 months of age). ASDs are clinically diverse, with the severity of the variety of symptoms, and the impairment they cause, varying extensively (Geschwind, 2009). Some community with an ASD also have an intellectual disability (low intelligence quotient; IQ), but at least 25% of those with ‘classic’ autism, and advanced proportion of those with milder ASDs, show normal or superior intellectual function (Rutter, 1983).

Autism Spectrum Disorder featuring both average range IQ and a history of ordinary language acquisition is called Asperger’s syndrome (Sharma, Woolfson, & Hunter, 2010). Nonetheless, it is debated whether Asperger’s is strictly a syndrome separate from autism (Wing, Gould, & Gillberg, 2011) and future DSM-5 diagnostic criteria would eliminate it as a separate diagnosis as well as be introducing additional changes to ASD diagnosis. ASDs are acknowledged to be highly genetic, with estimates of heritability ranging from roughly 0.5 to 0.9 (Ronald & Hoekstra, 2011). However, environmental factors, including perinatal and obstetric problems, also play a role (Gardener, Spiegelman, & Buka, 2011). First-degree relatives of affected persons are at augmented risk of an ASD, and also of milder social and communication impairments dubbed the ‘broader autism phenotype’ (Whitehouse, Coon, Miller, Salisbury, & Bishop, 2010). These studies provided a diverse picture. Clear cut abnormalities were identified in some individual cases of ASD, however, there was immense inconsistency in these researches outcome, with a range of diverse focal and generalized pathologies being reported in a wide range of studies.

The majority of persons with an ASD showed no qualitative abnormalities noticeable with such methods, although some quantitative differences were found, for example, reduced size of the corpus callosum and cerebellum, and amplified volume of the caudate nucleus in ASD, on standard, compared with controls, although with small or average effect sizes for a review and meta-analysis (Stanfield, McIntosh, Spencer, Philip, Gaur, & Lawrie, 2008). For example, near the beginning case reports recognized cerebellar hypoplasia and ventricular bulge in ASD cases (Courchesne, Hesselink, Jernigan, & Yeung-Courchesne, 1987) but other investigators reported no magnetic resonance imaging (MRI) malformation in nearly all cases, and normal cerebellar development (Garber, Ritvo, Chiu, Griswold, & Kashanian, 1989). In Asperger’s syndrome, many case reports of left temporal (Jones & Kerwin, 1990) left frontal and bilateral opercular cortical abnormalities (Berthier, Starkstein, & Leiguarda, 1990) were reported, with little consistency. MRI findings did not present a single pattern. Autism is a mixed disease entity containing various clinical subgroups, which do not demonstrate similar radiologic pictures (Nowell, Hackney, Muraki, & Coleman 1990).

Key Terms in this Chapter

Autism: Autism is a severe developmental disability which involves impairments in the social interaction like being unaware of other people's feelings as well as verbal and nonverbal communication. It is first seen within the first three years of life.

Autism Spectrum Disorder: A group with developmental disorders (such as autism and Asperger's syndrome) which is characterized by impairments in the capacity to communicate and interact socially by the occurrence of repetitive behaviors or restricted interests is called autism spectrum disorder. It is also known as pervasive developmental disorder.

Intelligence: Intelligence is the aggregate or global capacity of the individual to act purposely, to think rationally and to deal effectively with his environment.

Phylogeny: It is the expression of an evolutionary history of a species (and related species) through genes. These studies focuss on the progression and change of species throughout time and how similar species are connected through genetics and evolutionary time.

Diffusion Tensor Imaging (DTI): It is an MRI-based neuroimaging technique which makes it possible to estimate the location, orientation, and anisotropy of the brain's white matter tracts.

Neural Connectivity: Connections between neurons where neuron sends information via neurotransmitter.

Dorsolateral Prefrontal Cortex (DLPFC or DL-PFC): It is an area in the prefrontal cortex of the brain of humans as well as non-human primates. It is one of the most highly evolved part of the human brain. It undergoes a continuous period of maturation till adulthood. It is expressed like DLPFC or DL-PFC.

Executive Function: The term executive function is used by psychologists and neuroscientists to describe a loosely defined set of brain processes that are liable for planning, cognitive flexibility, abstract thinking, rule acquisition, initiating proper actions and inhibiting inappropriate actions, and selecting appropriate sensory information.

Morphometry: Morphometrics is derived from a Greek word morphe , “shape, form,” metria , “measurement.” Morphometry refers to the quantitative analysis of form, a concept that includes size and shape.

Precentral Gyrus: The precentral gyrus is a most important structure on the surface of the posterior frontal lobe. It is also the situated in the primary motor cortex known as Brodmann area 4.

Occipital: The occipital lobe is one of the lobes of the cerebral cortex in the brain of mammals. It is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The crucial visual cortex is Brodmann area 17, also known as called V1 (visual one).

Synapse: A synapse is a small gap at the end of a neuron that permits a signal to pass from one neuron to the other neuron.

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