Probing the Mind: Testing the breaking point of neuropsychological assessments
The applications of psychological research to medical and clinical evaluations are not always effectively communicated. Usually, psychological testing is associated with clinical psychology or psychiatry, and used only in evaluating for mental disorders, such as Autism Spectrum Disorder and Attention Deficit-Hyperactivity Disorder (ADHD). However, it is important to note that tests, or assessments, based on psychological concepts and research, are used to evaluate many different medical diseases. These tests are built to provide insight into language and other cognitive processes, so they are ideal for assessing neurological deficits or problems. In fact, they are often called neuropsychological tests or assessments for this reason. An example of one such test is the Western Aphasia Battery (WAB; Kertesz, 1982). This assessment is meant to detect the presence, degree, and type of aphasia in patients—aphasia being the inability or severe difficulty with speaking or understanding language. This kind of deficit can occur after stroke, brain injury, or other diseases that damage brain regions usually associated with language. But these assessments aren’t meant to just be in used in adults! Many have versions specifically made with children in mind. A very common IQ test called the Wechsler or WAIS, Wechsler Adult Intelligence Scale (Wechsler, 2008), has a version called WISC, or Wechsler Intelligence Scale for Children (Wechsler, 1949).
You may be wondering how exactly these assessments come about. Why and how do they make different versions for children and adults? How do they know how these tests can detect aphasia in patients? The simplest answer is that it takes a long time and a lot of effort. There’s a whole sub-field of psychology dedicated to exactly this: the theory and technique of measuring psychological concepts. When developing new assessment tools, usually it begins with a need: how can we detect the presence of such-and-such symptom or how can we measure and compare IQ across individuals? Once a need is identified, then questions, or items on the test, can start to be formulated. These items can take many different shapes from asking participants to matching vocabulary words to pictures—to asking someone to use colored blocks to match a given pattern. After a preliminary set of items are identified, they are tested over and over again across different individuals to see if they actually measure or answer the question that was initially asked. By the time these assessments are used by clinicians and researchers, they have been validated in healthy adults, or children, and, sometimes, in clinical populations like autism. Therefore, clinicians or researchers can trust the results of the test, because they know that there’s a lot of evidence to support them.
These assessments fare well in the majority of cases, but some issues crop up when trying to use them in very severe and complex cases of disease and disorders. An example of one such case is Krabbe (krab – ae) disease (KD.) KD is a leukodystrophy (luke-oh-diss-tro-fee), meaning that there is degeneration or damage to the white matter of the brain. The disease is caused by a mutation in a gene that codes for an enzyme important for breaking down toxic substances in the brain. As these substances accumulate, the shielding around the nerve’s gets damaged and fades. Without this shielding, the electrical pulses that nerves send to speak to one another no longer conduct properly and all those messages get confused. Symptoms and severity depend on the form of the disease: infantile, juvenile, or adult. But, in general, the damage to the shielding around nerves leads to cognitive and motor dysfunction and regression. It is a rare, estimated to occur in 1 in 100,000 live births, but is none-the-less a devastating disease.
Neuropsychological assessment is especially important in severe diseases such as KD as it allows clinicians to track progression of the disease and evaluate treatment steps. However, the severity and symptoms can impede and confuse evaluation. In its most severe form, infantile, the infants’ or child’s movements can be extremely restricted due to muscle weakness and muscle tone abnormalities. These issues with the musculature severely impair their ability to respond, with their eyes, by pointing, or vocally, to items on these assessments. Even questions or items that should probe cognitive ability would also probe motor abilities. So, how can you tell the difference between the child getting the item wrong because their cognitive abilities are impaired, or because they physically can’t respond to the question—no matter if they know the answer or not?
As you can see, this is a very important limitation to neuropsychological tests that likely would not have been found if not for these cases. Current research has been looking at how neurophysiological methods can be of help. These methods, such as electroencephalography (EEG,) refer to the use of machines to look at physiological changes in the brain. EEG is a recording of electrical brain signals from electrodes placed on the scalp. Using this method can give us a lot of additional information to that gathered from pure behavioral or neuropsychological assessment. For example, in sleep, EEG can be used to assess sleep issues as it allows clinicians to track different sleep stages. Without EEG, clinicians would need to wake patients up periodically and have them report on their sleep. EEG picks up certain signatures in the brain that indicate whether a person is in REM, in deep sleep. Clinicians can use this information to see if their patients are having difficulty falling asleep, or not having enough REM or deep sleep, amongst other issues. People can’t really tell you what sleep stage they were in very accurately when woken up abruptly every 30 or so minutes. In this same vein, EEG, along with other neurophysiological methods, are being investigated for their utility in the medical cases discussed above. So, although neuropsychological assessments work for a variety of clinical cases, there are some subset that really stretch their reliability and require the development of other methods for clinical assessment.
1. Kertesz, A. (1982). Western aphasia battery test manual. Psychological Corp.
2. Wechsler, D. (2008). Wechsler Adult Intelligence Scale–Fourth Edition (WAIS–IV). San Antonio, TX: The Psychological Corporation.
3. Wechsler, D. (2003). Wechsler intelligence scale for children-WISC-IV. Psychological Corporation.