Fonction exécutive dans les troubles du spectre autistique

Autism Spectrum Disorder is characterized by impairments in communication and executive function, with an onset that is often noted during early childhood.

Across normal development, children improve their executive processes, which include: flexibility—adapting thoughts in response to a changing environment; planning—the actions needed to attain a specific goal, and inhibition—being able to stop what they’re doing

However, in this social situation, the child who showed difficulty executing those functions—the one who didn’t go inside to get a coat because he kept waving a stick around—is an example of someone with components indicative of Autism Spectrum Disorder.

This video demonstrates how to perform a series of behavioral tests that tap into the processes of executive function in the laboratory, as well as how to analyze the data and interpret results in children diagnosed with Autism Spectrum Disorder compared to those without any known developmental disorders.

In this experiment, children with Autism Spectrum Disorder along with typically developing counterparts ages 6 to 18 are asked to complete three tasks—the Wisconsin Card Sorting Test, the Tower of London, and the Stroop Task—that measure different components of executive function.

In the first task, the Wisconsin Card Sorting Test, children are presented with four stimulus cards that incorporate three stimulus patterns: color, shape, and number.

They are asked to sort response cards according to one of these parameters, but the trick here is that they must figure out the sorting rule based on the feedback provided after matching each one.

Participants try sorting by color, shape, or number until they find the acceptable rule, which is applied for a run of 10 correct placements and then changed without warning.

The dependent variable then is the number of responses in which the participant continues to sort based on the previously correct rule, despite feedback that it was incorrect. This is known as perseveration: focusing on the same response even though it may not lead to an advantageous outcome.

The second task is the Tower of London, where participants must move disks from a prearranged sequence on three pegs to match a goal state in as few steps as possible. In this case, the dependent variable is number of moves made that surpass the minimum number necessary.

The third and final task is the Stroop test, where participants are asked to say out loud the colors of presented words. The colored terms are equally divided into either congruent trials—where the name and font color match, or incongruent ones—the two features are mismatched, for example, the word green is colored blue.

Here, the dependent variable is the time it takes for participants to say the correct color. Responses in the incongruent condition tend to be slower than congruent trials because participants must inhibit reading the word, which is fast and automatic, in favor of saying the actual color of the letters.

The symptoms of Autism Spectrum Disorder suggest deficiencies in the executive functions required to complete the three tasks. It is predicted that participants already diagnosed with the disorder will not have the same flexibility as controls with changing rules in the Wisconsin Card Sorting Test.

Likewise, they are also expected to demonstrate poor planning when solving the Tower of London, and reduced cognitive inhibition to correctly complete the Stroop test, compared to aged-matched and typically developing participants.

To begin, greet the recruited participant and have them sit comfortably in front of a computer. Note that all participants should be age- and intellect-matched. After gaining parental approval, guide them through the consent forms.

Now, explain to each participant that they will complete three tasks: first is the Wisconsin Card Sorting Test, where they have to match a single card to one of the four displayed on the screen. Elaborate that the cards can match in either color, shape, or number and that they will be told if their guess was correct or not.

Further inform them that, from time to time, the rule will change without notice and that they will have to discover the switch on their own to get as many as possible correct. Answer any questions they might have.

Then, start the task, and allow the participant time to complete the trials, which depends on either six runs of 10 correct placements or until all 64 cards have been sorted. When the task ends, provide them with a 2-min break.

Once the break is over, have the participant sit down again. Explain that the second task—the Tower of London—involves rearranging the configuration of three colored balls located on three pegs, and that their objective is to match the goal configuration in the shortest number of moves.

Also inform them that they should preplan the series of moves and to remember that a transfer cannot be undone. Following the instructions, allow them to complete 20 trials, using the mouse to execute their intended movements.

After another 2-min break, start the third and final test—the Stroop Task. Explain that in this case, a word will be displayed on the screen for up to 4 s, with 1.5 s in between each, and they are to say out loud, the color that the word is written in.

Note that the computer program logs reaction times based on the onset of the spoken color, over the course of 120 trials. You’ll still need to quickly record the participant’s verbalized responses and whether they are correct or not, between word presentations.

To analyze the data, evaluate each task individually: for the Wisconsin Card Sorting Test, determine the average number of perseveration responses; for the Tower of London, calculate the average number of excessive moves beyond the minimum required to solve each puzzle; and for the Stroop Task, average the difference in reaction times for naming the words in the incongruent compared to the congruent condition.

Plot the results for both control and autistic spectrum individuals across all tasks. First, in the Wisconsin Card Sorting Test, notice that participants with autism were less able to set-shift, or adjust to a new sorting rule mid-task.

In other words, they tended to get stuck in the card-sorting task and were unable to change their sorting strategy, which resulted in more perseverative errors.

In the Tower of London test, the autistic spectrum participants showed a deficit in the ability to solve the puzzle using the minimum number of moves, suggesting impairments in planning.

As for the Stroop test, both groups had the same reaction times, indicating that cognitive inhibition was not affected.

Now that you are familiar with several tests of executive function, let’s look at how such batteries could be used to diagnose and differentiate disorders with cognitive dysfunctions and possibly even lead to rehabilitation in these individuals.

While there are many neurodevelopmental disorders with impairments of executive function, including Autism, ADHD, and Tourette’s Syndrome, they may have differing executive profiles. For instance, as we’ve shown here, those with Autism Spectrum Disorders show deficits in the Wisconsin Card Sorting Test and Tower of London.

In contrast, children with ADHD demonstrate impairments in the Tower of London and Stroop Task, whereas those with Tourette’s Syndrome primarily display deficits in the Stroop Task.

Thus, if specific, yet differential, patterns of cognitive dysfunction can be identified across disorders, series of behavioral measures could be used as indicators during diagnosis.

In addition, understanding the cognitive differences amongst different disorders can lead to the development of more targeted rehabilitation programs, like using transcranial direct current stimulation.

Brain regions can be targeted, like the dorsolateral prefrontal cortex, before and after behavioral tasks. That way, researchers can measure whether stimulation enhances executive function, providing a promising approach for rehabilitating a number of disorders with distinct neural underpinnings.

You’ve just watched JoVE’s introduction to executive function in Autism Spectrum Disorder. Now you should have a good understanding of how to design and run a Wisconsin Card Sorting Test, the Tower of London test and the Stroop test, as well as how to analyze and assess the results.

Thanks for watching!