by Susan L. Hymian, M.D.
Assistant Professor of Pediatrics, Division of Developmental and Behavioral
Pediatrics
University of Maryland School of Medicine
The behavior an individual exhibits is determined by many factors in the internal and external environments. Characteristics such as cognitive impairment, language disorders, and motor disability impact on the way a person reacts to the world around them. Metabolic changes that directly or indirectly influence the nervous system can alter the way a person reacts to environmental stimuli or can provide an internal stimulus to engage in a behavior. In some circumstances, an underlying biologic abnormality results in behavioral dysfunction only when certain criteria in the external environment are also present.
There are several disorders that are associated with a specific behavior phenotype, or set of characteristics. For example, in the Lesch-Nyhan Syndrome where affected boys have cerebral palsy and an unusual pattern of self-biting behavior, neurochemical abnormalities have been identified.
The methods we have for studying the biologic basis of behavior are in the areas of neuroanatomy, neurochemistry, and neurophysiology. Anatomic investigations can use the imaging technology of the CT (Computerized Tomography) and MRI (Magnetic Resonance Imaging) scans to assess the size and shape of different brain regions in people. In experimental animal models, lesioning certain areas during different periods in development provides information on how brain development is affected and what areas of the brain control different behaviors. Neurochemical alterations can be assessed by response to different medications or by PET scan (Positron Emission Tomography) in people or by direct measurement in animal models. Measurement of the electrical activity of the brain can be assessed indirectly by such modalities as EEG and BAERs (Brainstem Auditory Evoked Response).
Maladaptive behaviors described in patients with Lowe's syndrome are similar to those described in children with developmental disabilities and visual impairment. These include food refusal, hyperactivity, stereotypic or self- stimulatory behaviors, tantrums, aggression, and self- injurious behavior. All of these behaviors can be influenced by environmental stimuli such as the need to communicate, to escape from a demanding situation, to obtain attention, or to provide stimulation.
Basic neurologic mechanisms may underlie or predispose an individual to these behaviors as well.
Food refusal may be prominent in children with metabolic disorders in which certain foodstuffs produce nausea. This avoidance can generalize to all foods. In some disorders, metabolic disturbance actually increases the production of the neurochemicals such as serotonin that turn off appetite. It is not yet known if this may be the case in patients in renal disease. Patients with oral motor dysfunction or gastroesophageal reflux will also exhibit food refusal.
Self-stimulatory behaviors seem to be mediated by the neurotransmitter dopamine in certain areas of the caudate nucleus of the brain. Similarly, aggression can be localized to the limbic system of the brain and hyperactivity to the function of the neurotransmitters dopamine and norepinephrine in inhibitory systems. Our understanding of the clinical meaning of these findings and treatment options is still evolving.
Behavior needs to be viewed as an interaction of the individual and the environment. The ongoing efforts to determine if a specific behavioral phenotype exists in Lowe's syndrome will help guide medical and behavioral investigators to identify which particular neurologic systems are involved and may lead to clinical interventions specifically targeted for abnormalities that are found.
On The Beam Winter/Spring, 1990 (9:1)
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