Article review: "Development and validation of the Arizona Cognitive Test Battery for Down syndrome" by Edgin and colleagues

Posted 10:37 AM, December 20, 2010, by wetmore

My first posting about DS scientific literature is an important study published earlier this year by Jamie Edgin, Lynn Nadel, and an all-star cast of colleagues titled "Development and validation of the Arizona Cognitive Test Battery for Down syndrome."

The Arizona Cognitive Test Battery (or ACTB) is quickly becoming the center of conversation among Down syndrome researchers and clinicians interested in assessing cognitive abilities and disabilities in children, adolescents, and adults with Down syndrome.

(Click below to continue reading...)

My first posting about DS scientific literature is an important study published earlier this year by Jamie Edgin, Lynn Nadel, and an all-star cast of colleagues titled "Development and validation of the Arizona Cognitive Test Battery for Down syndrome."

The Arizona Cognitive Test Battery (or ACTB) is quickly becoming the center of conversation among Down syndrome researchers and clinicians interested in assessing cognitive abilities and disabilities in children, adolescents, and adults with Down syndrome.

Before I dive into a discussion of the study, a few words about the authors. The first author, Jamie Edgin, is an amazing resource for the entire Down syndrome community. For the past ten years or so, she has been working on cognitive assessment tools for individuals with Down syndrome and other neurodevelopmental disorders. These days she works with Prof. Lynn Nadel at the Down syndrome research group at the University of Arizona. Lynn Nadel--quite literally--wrote the book on the hippocampus, a brain region critical for learning and memory.

The rest of the authors list includes a whos-who of respected Down syndrome researchers and clinicians, many of whom I've had the pleasure to meet: George Capone at Kennedy Krieger in Baltimore; Roger Reeves at Johns Hopkins; and Stephanie Sherman at Emory.


Why this study is important:

Researchers and doctors require reliable and sensitive tests of cognitive function designed specifically for individuals with Down syndrome (DS). Children with DS develop at different rates from other children, with strengths and weaknesses in particular cognitive domains. Tests designed to evaluate these cognitive domains in a simple and non-verbal way are critical. Standard IQ tests are less effective for assessment.

Before Jamie Edgin and colleagues developed and evaluated the ACTB, commonly used and widely available cognitive tests just weren't appropriate for people with DS. Hopefully, the ACTB will become a standard for cognitive research, permitting a better understanding of normal development in DS. Hopefully it will also form a foundation for studies to investigate how educational, behavioral, or drug interventions affect cognitive abilities in DS.

While developing this set of tests, Jamie and colleagues also learned simple but important tricks to make sure the test subjects were focused & motivated (a good night's sleep, healthy snacks to stay on task, parents connected by video in the next room, etc). These protocols will be very helpful as the ACTB as a research tool spreads more widely.


Results and interpretations:

Over a period of many years, the authors evaluated a variety of existing and novel tests to determine which were most appropriate for children and adolescents with Down syndrome. They chose specific tests from existing cognitive test batteries that have been well-validated in typical children, such as the CANTAB test battery. In some cases, they also developed tests from scratch. The criteria for choosing this set of tests included:

  • Capacity to assess a range of skills
  • Non-verbal tests so that even children with poor language skills can be assessed
  • Reliable tests that are sensitive enough to find small differences in abilities between individuals or across time
  • Correlation with brain function in regions known to be affected in DS, such as the hippocampus (long-term memory) and cerebellum (motor control)
  • Applicability across a range of ages and abilities, socio-economic backgrounds, ethnicities, and testing environments

Based on these goals, the authors created a test battery that can be completed in a single two hour test session. The ACTB is computer-based and requires minimal verbal skills. Multiple sub-tests assess similar cognitive functions, so even if a subject does not complete on of the tests, cognitive assessment is still possible. Cognitive domains assessed and example tests are:

  • Prefrontal cortex, a brain region important for executive control and decision-making. The 'modified dots task' asks subjects to click a button below an image of a frog or cat, with rules for choosing that change over time. (e.g. 'click the cat' or 'don't click the frog').
  • Hippocampus, a brain region important for forming long-term memories. In the virtual computer-generated arena, subjects use a joystick to explore a virtual room to find the location of a previously presented hidden object.
  • Cerebellum, a brain region required for well-controlled movements. In the finger tapping task, subjects click a button with a sequence of finger taps.

To assess performance, the authors tested 74 individuals with DS between the ages of 7-38. They also tested 50 typically developing children ages 3-8 to compare performance in specific cognitive domains to DS individuals. Importantly, individuals tested completed most of the tests and re-testing in a subset of subjects showed that similar results could be reliably reproduced. As expected, in many tests of these cognitive domains, individuals with DS showed deficits relative to age-matched typically developing control subjects.


What's next:

Future projects include rolling out the testing program to new sites (including, we hope, Stanford!), testing a wider range of ages and abilities, and following children from year to year to assess educational and cognitive growth. The ACTB also will permit companion studies to understand how other disorders present in the DS population (such as autism) affect cognitive performance and development. In the future, clinical studies that assess the effectiveness of drugs to enhance cognitive abilities in DS may use the ACTB to measure changes in cognitive function.

The authors have openly shared details about the test battery and their cognitive testing strategies. Unfortunately, many of the tests in the ACTB are from test libraries such as CANTAB that are not freely available. Though many research and cognitive testing centers do have the necessary software licenses, this means that the ACTB is not appropriate for DIY at home. The ACTB requires a well-trained tester to ensure standardized test protocols.

The ACTB tests are largely non-verbal, meaning that applying these tests to ESL communities in the US and non-English speaking communities around the world is possible as well. By expanding the number of test sites, testing will be available to more families and the data generated will form the foundation for a better understanding of cognitive development in DS.

If you have any questions, please don't hesitate to post a comment here or email me.


Due to copyright rules, I am not allowed to post the manuscript here. The full reference and a link to the online journal are here:

Edgin et al. Development and validation of the Arizona Cognitive Test Battery for Down syndrome. J Neurodev Disord (2010) pp. 1-16
http://www.springerlink.com/content/p8387h045u414192/

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