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Neurodevelopment and Autism
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Autism
is a mental disorder that afflicts a multitude of patients, having
lifetime effects on their cognitive and social abilities.
Normal
development of the fetus during pregnancy is precise and needs to
maintain proper order of development in order to grow correctly to give
the new infant a chance at normal neural development and thus, a
healthy life. This process of development can be easily disrupted though. These disruptions in development can lead to serious problems awaiting the newborn child. These
developmental problems can be caused by numerous factors, either
internal or external, to the fetus, which lead to the possibility of
severe mental disorders. Most children and
parents never experience these types of disabilities and hardships, but
there are also many that do suffer the terrible outcomes of
abnormalities during neurodevelopment. There are many of these types of abnormalities in development, and many types of disorders as well. These disorders can also range in severity according to the amount of unusual development of the nervous system of the infant. Even
after birth, the first few years of the infantÂ’s life are very
important to proper development of the body and nervous system, and the
newborn can still undergo serious problems and fall prey to serious
mental disorders. One such type of mental disorder associated with improper neural development is autism. Improper development of the nervous system can lead to multiple problems and affect the rest of the childÂ’s life.
Normal
neurological development generally occurs in the same pattern with
every person, and follows steps or stages of development at different
times in the growth of the fetus during pregnancy. These
steps of growth are regulated by numerous hormones and
neurotransmitters found in the body at early stages of development,
such as serotonin. Serotonin is thought to
“regulate the development of target tissues and other serotonergic
neurons” (Whitaker-Azmitia, 2001, p.479) which eventually leads to the
proper growth of cells at their designated areas to operate properly. Serotonin
is different from other hormones and neurotransmitters in that after
development and birth, only about two percent of the serotonin found in
the body is found in the brain, and the rest is located in the abdomen. Most other neurotransmitters found in the brain during development are usually found in great quantity after birth as well. Also, serotonin levels slowly decline to adult levels at around five years of age (p.479). Serotonin also effects neurogenesis, synaptic maintenance and synaptogenesis, dendritic development, and cell migration (p.480). Other
neurotransmitters used in the normal growth of the central nervous
system are dopamine, glutamate, glycine, as well as many more. Dopamine, for instance, has been found to control neurite outgrowth, as well as neuron branching (Todd, 1992, p.802).
There are five major stages in normal neurodevelopment. The
first stage occurs during the third or fourth weeks of development,
when a patch of tissue develops into the neural plate, which will
eventually develop into the nervous system. The neural plate folds over and becomes the neural groove. Over
time, the neural groove will pinch shut, and form the neural tube,
which is the beginning of the spinal cord and cerebral ventricles. While the neural tube is forming, the neural crest also forms. The neural crest eventually becomes the peripheral nervous system, neurons, and glia cells. Near
the end of this first stage, around the sixth month of development, the
beginnings of the forebrain, midbrain, and hindbrain develop. These
three parts of the brain are the basic foundations and sections of the
fully developed human brain, which is why it is important for these
three to properly develop. The second stage of neural development is marked by rapid growth of neural cells after the neural tube is formed. The cells divide and multiply in the ventricular zone of the immature brain.
The
third stage is the migration of neural cells out of the ventricular
zone, along radiating glia cells to their appropriate location. During this migration, cells move through different zones, or layers, of the brain. The cells can either move directly through these layers, or stay and develop there to become specialized. An example of this would be cells migrating to the subventricular zone and becoming either glia cells or interneurons. Wherever
the cells migrate to, when they reach their final destination, they
begin to group themselves together, or “aggregate”, based on their
similar functions, and stay together due to cell-adhesion molecules, or
CAMs. After the cells have aggregated together, they begin to grow axons and dendrites. These axons and dendrites must grow to their correct target in order to function properly. This growth is associated with the fourth stage of development.
Finally,
because the brain develops 50 percent more neurons than the brain will
ever need or use, the fifth stage is involved with neuron death and
synapse rearrangement. Because of the extra cells, this causes competition between neurons to find their correct targets. If they do not reach the correct target, they will not receive the neurotropin, which preserves their life. This competition ensures that only the strongest neurons will survive to be used by their nervous systems. When the neurons die, their vacancies are filled with axon terminals of surviving neurons. This increases the selectivity of transmission in the brain.
The brain does not stop developing after birth. The brain quadruples in size until adulthood. This is due to the formation of new synapses, increased myelination of axons, and increased branching of dendrites. Also,
because of increased hormonal secretions, puberty is a time when “the
brain is subject to development of neural circuits involved in mental
health and illness” (Walker, 2002, p.24). These changes involve the “maturation of the frontal and temporal cortex, amygdala and hippocampus” (p.25). Also, there is decreased grey matter in the cortex, increased myelination, and increased density of the white matter (p.25). The
increased myelination increases the speed of neural transmissions by
surrounding the axons in a lipid layer that promotes electrical neural
impulses, thereby allowing for thoughts and actions in the brain to be
carried out faster. This increased
myelination is the cause of the increased density of white matter
because white matter is made of neurons with myelinated axons.
There
are also many different ways that this development of the brain can be
altered, and the mental health of the individual can be compromised and
changed. Maternal deprivation causing stress leads to increased neuron and glia cell death in infant rats (Zhang, 2002, p.2). A
lack of glycogen synthase leads to genetic malfunctions and defects,
which causes abnormal gene development in the brain (Kozlovsky, 2002,
p.14). Genetic and environmental factors
can interfere with maturation and development of certain specialized
cognitive areas of the brain, such as the ontogenic area (DeCaria,
1999, p.136). Improper nutrition of the
mother can lead to the lack of proper vitamins and minerals being
provided to the fetus (Guesry, 1998, p.190). Toxins found in the area lead to increased apoptosis of healthy neurons (Stahl, 1997, p.184). Mutations in CAMs lead to cells aggregating in the wrong places with the wrong types of cells (Wong, 1995, p.169). All of these possible dysfunctions and abnormalities can lead to any number of mental illnesses in the child. One of the more common mental illnesses found in children is autism.
Autism
is a mental disorder primarily diagnosed in early years of childhood
that usually develops within the first three years of life and lasts
the personÂ’s lifetime. Like other diseases,
it has different levels of severity and also has multiple symptoms that
are seen in almost all cases of children with the disease. There are three main signs that signal that a child has autism. Autism
causes problems with both verbal and nonverbal communication, reduced
social interactions, and preoccupation with objects or activities,
which leads to routine, repetitive behavior (NICHD website, 2002). There are also several physical abnormalities, such as low-set, square-shaped ears that have tops that flop down. Also, autism is associated with lack of control of the face, mouth and eyes. The
major symptoms cause the autistic child and family to encounter
multiple problems and cause difficulties in their daily lives. Autistic children may not look others in the eye, and may also not want to be held or hugged by any other people. Other mental illnesses in children have the same symptoms of autism, just slightly altered. A
child with AspergerÂ’s Disorder has impaired social interactions and
preoccupation with objects or activities, but do not display the lack
of communication that autistic patients do. Also,
a child inflicted with Childhood Disintegrative Disorder will develop
for the first two or three years of their life normally, but will
suddenly acquire all of the symptoms of autism. Because
these two disorders are fairly similar to autism, finding a cure for
autism will perhaps lead to a cure for these mental disorders as well.
Communication
problems are also common in children with autism and may be early
warning signs of an infant that may have the disorder. These
communication problems may be such things as not babbling or gesturing
to others by 12 months of age, not saying single words by 16 months of
age, or the loss of language ability at any age (NICHD website, 2002). A childÂ’s doctor may also be able to identify certain markers that may signal that a child has the beginning stages of autism. A
doctor would look for a child “not responding to their own name,
delayed development of language skills, throwing random temper
tantrums, the child being hyperactive or uncooperative, getting
occupied with one thing and not being able to move onto another, being
in their ‘own world’, walking on their toes, and not being able to play
with toys” (NICHD website, 2002). These are all common signs that a child has autism.
While autism is not very common, it is also not altogether rare. “It is estimated that one in 500 – 1000 cases of autism are diagnosed each year in the United States alone” (NICHD website, 2002). Also, it appears to be far more common in males than females. About 75 percent of all autistic cases are found in males (Pinel, 2003, p.235). Having autism does not necessarily mean that the child is mentally retarded either. Another 75 percent of total cases of autism are also mentally handicapped (p.235). Another determining factor of whether or not a child will be autistic is due to family history. If
a family already has a child with autism, there is a five to ten
percent chance that they will have another child with autism, whereas a
family without a child with autism has a less than one percent chance
of having an infant with the disease (NICHD website, 2002). It has also been determined that about one in ten people with autism are savants. Savants are individuals that possess extraordinary skills at cognitive or artistic abilities (Pinel, 2003, p.510).
Autism
is caused by abnormal defects occurred during neurodevelopment of the
fetus, but the exact cause of the abnormal development is still unknown. Some professionals believe that developmental problems that cause autism are due to serotonin increase in the blood. “High levels of serotonin in the blood would lead to a loss of serotonin terminals in the nervous system. This
loss could then cause altered developmental processes in target areas,
such as decreased dendritic branching in the hippocampal formation and
lack of maturation of the hippocampus which leads to fewer connections
with the cortex” (Whitaker-Azmitia, 2001, p.481). More
support for the idea that lack of serotonin is associated with autism
is that in the raphe nuclei, which are a major part of the serotonin
system of the brain, do not have a decreased number of cells, but that
the cells that are there have underdeveloped processes or no processes
at all (p.481).
While
studies have shown lack of serotonin receptors leads to
underdevelopment of the brain, postmortem autopsies of autistic
personsÂ’ brains shows still more evidence of lack of neurodevelopment. They have found that individuals suffering from autism tend to have shortened brainstems in the pons area. Also,
they tended to have underdeveloped facial nerves, which explains the
lack of facial control, and also totally lacked the superior olive,
which has important roles involved in sound localization (Pinel, 2003,
p.236).
Although
there is no cure found for autism yet, there are multiple treatments
available for physicians, psychologists, and psychiatrists to use. If
the disease is found early enough and if the treatments begin soon
after discovery, then the child has a good chance of overcoming most of
the major symptoms and will be able to lead a normal life. Individualized education programs have been found to be highly effective in treating the disease. It works with patients to overcome specific problems caused by the mental illness. The
specialist would work one-on-one with the child to help them get over
one aspect of the disease, and then move onto the next one if needed. Another program similar to the individualized education program is the applied behavior analysis. In this treatment, the doctor would work to reduce problem behaviors and replace them with new healthy skills. Positive
behavioral interventions and support is a type of treatment that looks
at the patientÂ’s environment and behavior to increase positive
behaviors and decrease negative behaviors in order to develop the best
lifestyle for the child. Finally,
medications are typically used to treat specific behaviors, and also
used to treat the comorbid conditions usually found with autism, such
as seizures or sleep disorders.
Neurodevelopment of a fetus is highly organized, very precise, and crucial to proper development of the rest of the body. But this process can be easily disrupted, causing any number of possible mental or physiological problems. These
mental illnesses, no matter how small, can place major strain on the
newbornÂ’s family, and also make the rest of the infantÂ’s life very
difficult. Autism is no exception to this idea. Even
though the cause for the neurological underdevelopment is still
unknown, and a cure has not yet been found, early detection along with
new treatments being provided can assure that the child has the best
possible chance of dealing with the hardships caused by this disease.
References
DeCaria, C., & Aronwitz, B., & Calev, A (Eds.). (1999). Assessment of Neuropsychological Functions in Psychiatric Disorders. Washington, D.C.: American Psychiatric Association.
Guesry, P. (1998). The Role of Nutrition in Brain Development. Preventive Medicine: An International Journal Devoted to Practice and Theory, 27(2), 189-194.
Kozlovsky, N., & Belmaker, R. (2002). GSK-3 and Neurodevelopmental Hypothesis of Schizophrenia. European Neuropsychopharmacology, 12(1), 13-25.
Pinel, J., & Merrill, C (Eds.). (2003). Biopsychology. New York, NY: Pearson Education, Inc.
September 3, 2002. Health Information and Media Publications: Autism Facts. Retrieved November 10, 2002, from http://www.nichd.nih.gov/publications/pubs/autism/facts/index.htm
Stahl, S. (1997). Apoptosis – Neuronal Death by Design. Journal of Clinical Psychiatry, 58(2), 183-184.
Todd, R. (1992). Neural Development Is Regulated by Classical Neurotransmitters: Dopamine D2 Receptor Stimulation Enhances Neurite Outgrowth. Biological Psychiatry, 31(8), 794-807.
Walker, E. (2002). Adolescent Neurodevelopment and Psychopathology. Current Directions in Psychological Science, 11(1), 24-27.
Whitaker-Azmitia, P. (2001). Serotonin and brain development: Role in human developmental diseases. Brain Research Bulletin, 56(5), 479-485.
Wong, E. (1995). Mutations in cell adhesion molecules L1 cause mental retardation. Trends in Neuroscience, 18(4), 168-172.
Zhang Li, X. (2002). Maternal Deprivation Increases Cell Death in the Infant Rat Brain. Developmental Brain Research, 133(1), 1-11.
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