Wednesday, 11 June 2014

Myelin

The research study that we were part of was studying how the brain develops by imaging myelination in typical development and in individuals with autism.

Myelin is an insulating layer, or sheath, that forms around nerves, including those in the brain and spinal cord. It is made up of protein and fatty substances.
The purpose of the myelin sheath is to allow electrical impulses to transmit quickly and efficiently along the nerve cells. If myelin is damaged, the impulses slow down.
Myelin is a dielectric (electrically insulating) material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. It is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination. In humans, myelination begins in the 14th week of fetal development, although little myelin exists in the brain at the time of birth. During infancy, myelination occurs quickly and continues through the adolescent stages of life.

Myelin is made up by different cell types, and varies in chemical composition and configuration, but performs the same insulating function. Myelinated axons are white in appearance, hence the "white matter" of the brain. The fat helps to insulate the axons from electrically charged atoms and molecules. These charged particles (ions) are found in the fluid surrounding the entire nervous system. Under a microscope, myelin looks like strings of sausages. Myelin is also a part of the maturation process leading to a child's fast development, including crawling and walking in the first year.


Is Myelin Content Altered In Young Adults with Autism?

Background:
There is increasing evidence that autism is associated with abnormal white matter development and impaired ‘connectivity’ of neural systems.  Brain connectivity is mediated by myelinated axons, which may be altered or abnormal in autism.  However, to date, no study has directly investigated brain myelin content of autistic individuals in vivo.
Objectives:
The primary objective of this study is to elucidate differences in myelin content in typical and autistic brains. The ultimate aim is to improve our understanding of the underlying neurobiology of autism using non-invasive magnetic resonance imaging (MRI) techniques,
Methods:
Using a new myelin-specific magnetic resonance imaging technique, termed mcDESPOT, brain myelin content was compared between 14 young adults with autism, and 14 matched controls.  Relationships between myelin content and clinical symptom severity within the autistic group (measured by the Autism Diagnostic Instrument, ADI-R); and the severity of autistic traits in both cases and controls, using the Autism Quotient (AQ).
Results:
Individuals with autism demonstrated a highly significant (p < 0.0017) reduction in myelin content in numerous brain regions and white matter tracts.  Affected regions included the frontal, temporal, parietal and occipital lobes.  White matter tracts most affected included the corpus callosum; the uncinate and posterior segments bilaterally; left inferior occipitofrontal tract and cerebellar peduncle, arcuate fasiculus and inferior and superior longitudinal fasciculi; and the right anterior segment.  Further, within autistic individuals, worse interaction score on the ADI-R was significantly related to reduced myelin content in the frontal lobe; genu of the corpus callosum; and the right internal capsule, optic radiation, uncinate, inferior frontal occipital fasciculus and cingulum.  Additionally, increased autistic traits in both cases and controls were significantly related to reduced myelin content of the left cerebellar; genu of the corpus callosum; and left temporal lobe white matter. 
Conclusions:
Individuals with autism have significantly reduced myelin content in numerous brain regions and white matter tracts.  We also provide preliminary evidence that reduced brain myelin content is associated with worsened social development in autistic individuals, and increased autistic traits in both cases and controls.

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