Rosenberg‐Lee, M., Ashkenazi, S., Chen, T., Young, C. B., Geary, D. C., & Menon, V. (2015). Brain hyper‐connectivity and operation‐specific deficits during arithmetic problem solving in children with developmental dyscalculia.Developmental science, 18(3), 351-372.http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4320038/
In this research done with 7-9 year old
children, the authors compared addition and subtraction abilities of children with
developmental dyscalculia (DD) and typically developing children (TD).
Children
diagnosed as DD scored at or below the 25th percentile on the Numerical Operations subtest of the Wechsler
Individual Achievement Test – Second Edition; WIAT-II. Children diagnosed as TD scored at or above
the 75th percentile on this test.
Children in both groups had a FSIQ of 80 or above, and scored at or
above the 25th percentile on the Word
Reading subtest of the WIAT-II. Sixteen
DD and 20 TA children participated in
the study.
The fMRI experiment
consisted of addition and subtraction problems which were either simple or
complex. Each calculation trial lasted five
seconds. In the Complex addition task,
participants were presented with an equation involving two addends and asked to
indicate, via a button box, whether the answer shown was correct or incorrect
(e.g. ‘3 + 4 = 8’). The first operand ranged from 2
to 9, the second from 2 to 5 The
Simple addition task was identical except that one of the operands was always
‘1’ (e.g. ‘3 + 1 = 4’). In the Complex subtraction task, the first operand
ranged from 3 to 14 and the second operand from 2 to 5. In the Simple
subtraction task, the first operand ranged from 2 to 14 and the second operand
was always ‘1’.
Here I'll
focus on a few findings that are of interest for me, and not on all findings of
this study.
·
DD children solved addition
tasks with the same level of accuracy as TD children, but were slower. DD children were significantly deficient with
the subtraction tasks, in comparison with the TD children. Children with DD failed to respond in
the allotted time in a large proportion of trials during the subtraction task.
However, for trials in which they made a response, accuracy in the DD
participants was relatively high at 75.4%, suggesting that DD participants were
actively engaged in the task but were unable to solve many of the problems with
the same fluency as their TD peers.
·
Timed trials exacerbate the
difficulties children with DD have when solving subtraction problems consistent
with their difficulties on timed number fact and story problems. The latter are
typically due to use of slower and more effortful counting strategies to solve
the problems, as contrasted with direct retrieval of the answer in children
without mathematical difficulties. This pattern may be
exacerbated with subtraction because, unlike addition, subtraction problems are
not commutative (e.g. 4 − 3 ≠ 3 − 4), which makes memorization of answers more
difficult and thus results in less fluent problem solving for all students.
·
Children
with DD engage multiple fronto-parietal circuits differently from TD children.
Children with DD may require greater engagement of these circuits, even while
achieving only weaker levels of performance. Alternatively, greater engagement of these circuits may result in the
activation of problem-irrelevant information that in turn disrupts problem
solving. The latter view is consistent with behavioral studies that show the
intrusion of problem-irrelevant information into working memory when children
with DD attempt to retrieve arithmetic answers from long-term memory.
·
Hyper-connectivity, rather than gross under-activation, is the primary
neural source of problem solving difficulties in children with DD. DD children showed hyper-activation on both addition and subtraction problems in multiple
frontal, parietal and visual areas. Children with DD showed especially high
levels of hyper-activation in parietal cortex for both correctly and
incorrectly solved subtraction problems.
·
There is a network
of brain regions that show aberrant responses during arithmetic problem
solving. Arithmetic deficits in DD are
unlikely to be localized to a single brain region. Rather, both localized
processing deficits in multiple brain areas as well as the coordination between
multiple brain circuits are impaired in DD. These conclusions are consistent
with the proposal that most neurodevelopmental disorders and learning
disabilities arise from diffuse disruptions and aberrant connectivity between
regions rather than focal lesions.
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