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Abstract:
Functional MRI was used to compare brain activation
associated with the specific arithmetic operations, namely,
multiplication and subtraction. This was inspired by a case of 56
y. o. woman who suffered from an intracranial hemorrhage at left
parieto-temporal region and showed a rare dissociation in
performance of the arithmetic operations; namely that her
multiplication was severely impaired, while subtraction was largely
intact. T2*-weighted images were obtained in 1.5 T General Electric
MR scanner with EPI gradient echo sequence, while 11 normal
subjects performed alternatingly multiplication and subtraction
between identical pairs of one-digit numbers. Comparison between
the two arithmetic conditions revealed activation significantly
higher with multiplication than with subtraction at left
supramarginal gyrus, left superior frontal gyrus, and bilateral
precunei, and the reverse, i.e., higher signal with subtraction
than with multiplication, at bilateral superior parietal lobules.
Talairach coordinates of multiplication-higher activation at left
supramarginal gyrus matched exactly with those of the lesion of the
above-reported case, while adjacent region matching
subtraction-higher activation was normal in the patient. The
findings from the case-report and fMRI experiments demonstrate that
distinct cortical areas are differentially involved in the two
arithmetic operations, and support the notion that multiplication
is carried out by retrieval of verbal rote memory of number-facts,
while subtraction is performed by manipulating analog
representation of quantity.
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