Heritability of Stroop and flanker performance in 12-year old children
BMC Neuroscience
Heritability of Stroop and flanker performance in 12-year old children
John F Stins 1
G Caroline M van Baal 1
Tinca JC Polderman 0 1
Frank C Verhulst 0
Dorret I Boomsma 1
0 Department of Child and Adolescent Psychiatry, ErasmusMC-Sophia Children's Hospital , PO Box 2060, 3000 CB Rotterdam , The Netherlands
1 Department of Biological Psychology, Free University of Amsterdam , Van der Boechorststraat 1, 1081 BT Amsterdam , the Netherlands
Background: There is great interest in appropriate phenotypes that serve as indicator of genetically transmitted frontal (dys)function, such as ADHD. Here we investigate the ability to deal with response conflict, and we ask to what extent performance variation on response interference tasks is caused by genetic variation. We tested a large sample of 12-year old monozygotic and dizygotic twins on two well-known and closely related response interference tasks; the color Stroop task and the Eriksen flanker task. Using structural equation modelling we assessed the heritability of several performance indices derived from those tasks. Results: In the Stroop task we found high heritabilities of overall reaction time and - more important - Stroop interference (h2 = nearly 50 %). In contrast, we found little evidence of heritability on flanker performance. For both tasks no effects of sex on performance variation were found. Conclusions: These results suggest that normal variation in Stroop performance is influenced by underlying genetic variation. Given that Stroop performance is often hampered not only in people suffering from frontal dysfunction, but also in their unaffected relatives, we conclude that this variable may constitute a suitable endophenotype for future genetic studies. We discuss several reasons for the absence of genetic effects on the flanker task.
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Background
The Stroop test [1] is arguably the best-known
neuropsychological test to tap attentional (dys)function. In the
color words version of this test the instruction is to attend
to the color of the ink in which a word is printed and
name this color aloud. At the same time, the printed
words may also read certain color names that are different
from the color of the ink in which it is printed. As has
been observed on numerous occasions, there is a strong
tendency to respond to the content of the word, and not
to the ink color. This is evidenced by an increase in
response time and a decrease in accuracy relative to a
neutral control condition.
The Stroop test has been used both to tap fundamentals of
human information processing (e.g. [2]), and as a clinical
aid to assess attentional dysfunction, e.g., due to a frontal
or fronto/parietal deficit. Brain imaging and neurological
studies consistently point to the prefrontal cortex (PFC) as
the site involved in resolving the response conflict. As a
consequence, people suffering from attentional
impairments, caused by prefrontal abnormalities
(developmental or acquired), tend to suffer more from Stroop
interference than controls. For example, the test
succesfully differentiates unaffected controls from people
suffering from schizophrenia (e.g., [3]). In a similar vein,
people suffering from attention-deficit/hyperactivity
disorder (ADHD) suffer from Stroop interference ([4]; see
also [5]), although a recent meta-analysis cast some doubt
about the usefulness of the Stroop task in differentiating
people with ADHD from controls [6].
There now exist numerous versions of the Stroop test. For
example, instead of using color words, researchers have
adopted more ecologically relevant items, such as
emotion words, pictures of food items or of threatening
objects, etc. In addition, it is now also common to use
computerized versions of the Stroop task, permitting a
trial-by-trial analysis of performance. But what all these
different Stroop versions have in common is that the
subject is always presented with a stimulus that
simultaneously activates two conflicting response channels; one
response is activated by the instructions, whereas the
other response is activated by elements in the array that
strongly invite an alternative yet incorrect response. In
order to resolve this response conflict the subject has to
direct attention to task relevant information and ignore
information from the task irrelevant channel. The time
needed to resolve this conflict is derived using subtractive
logic, and can be used as an index of the efficiency of the
attentional system under investigation.
A task that is less widely used in clinical circles, but that
also indexes the efficiency of the frontal network is the
Eriksen flanker task. In the arrow version of this task,
subjects have to respond to the direction of a left or right
pointing arrow, and ignore flanking arrows that point in
the opposite direction as the target arrow [7]. Similar to
the Stroop task, there is a tendency to respond to the
distracting flanker elements, and subjects have to resolve this
respon (...truncated)