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  » Types of Intelligence

  » Intelligence, Heredity, and Environment
        Evidence for Nature
        Evidence for Nurture
        Comments on Research

  » Neuropsychological Testing
        Normal Intelligence
        Abnormal Examination             and Brain Trauma

  » Spectroscopy Data

  » Disorders related to Intelligence

  »  Gender Differences
       Self-Estimated              Intelligence
       Anatomical Differences
       Gray vs. White Matter

  » Artificial Intelligence
        A Timeline of AI
        Ancient History of AI
        Modern History of AI
        The Future of AI

  » Age and Intelligence
        Areas of Function
        Effects of Lesions

  » References

Disorders Related to Intelligence

  There is a large discrepancy between premorbid estimators of IQ (as described above) and recent IQ measures. This gap increases as the severity of the disease increases. The tests explained in the premorbid IQ section (the National Adult Reading Test, the Wide Range Achievement Test, and the Ammons Quick Test) show discrepancies from the WAIS Full Scale IQs in those elderly patients diagnosed with mild and moderate Alzheimer's disease.

Dementia is characterized with the loss of normal intellectual functions, like thinking, remembering, and reasoning. Dementia is often severe enough to interfere with a person’s daily functioning. While Dementia is not actually a disease itself, it is rather a group of symptoms that may accompany certain diseases or conditions, such as Alzheimer’s. Some first symptoms may include changes in personality, mood, and behavior. Dementia is irreversible for the majority of cases. Similar to Alzheimer’s, patients will show a large disparity between premorbid and current IQ. Moreover, the IQ also decreases significantly as the patient’s Dementia progresses.

A stroke is characterized by interruption of the blood supply to a section of the brain by occlusion or by hemorrhage. Occlusion (referred to as ischemia) is a reduction of blood flow due to obstruction in the brain. This type of stroke is the most common. A hemorrhagic stroke occurs when a blood vessel in the brain ruptures. This causes blood to escape into the areas surrounding the brain cells. A stroke generally presents with loss of function of the contralateral side of the body controlled by the affected part of the brain. Due to the nature of a stroke, it is sometimes possible to recover premorbid functioning. However, it can also be the case that someone who suffers a stroke will not be able to recover functioning completely. Therefore, there is a wide range of IQ discrepancies noted from premorbid functioning, especially because a stroke may affect any wide range of areas in the brain, which may not directly affect IQ.

There are a number of different learning disabilities that may affect functioning, and specifically IQ. A learning disability may affect the person’s capacity to write, read, speak, pay attention, hear, and problem solve for example. One problem that may be an underlying cause for learning disabilities that is often diagnosed is called Attention Deficit/Hyperactivity Disorder (AD/HD). AD/HD is a neurobehavioral disorder that generally is characterized by a child’s hyperactivity, impulsivity, and inattention greater than most kids of the similar age or developmental level. Those with learning disabilities are most likely similar in IQ as those in their developmental level. The problem mostly lies in an inability to correctly make connections and learn which can often be partly solved by medications. It appears as though those with learning disabilities can easily have the same IQ as the normal population.

Mental retardation can also take on many forms. Because such disorders affect the brain usually in total, IQ is most often lowered. In mild to moderate cases, an average IQ may fall between 60-85 on the WAIS scale.