Deficits in short-term memory for serial order in adults with developmental dyscalculia: Evidence from fMRI

Verbal short term memory (STM) impairment is an associated and long-lasting deficit in developmental dyscalculia, but the nature of this impairment is poorly understood. Recently, a close association between numerical development and STM for serial order has been observed and has led to the hypothesis that STM for serial order and numerical abilities depend on common ordinal representations supported by the right intraparietal cortex. The aim of this fMRI study was to explore the neural correlates of STM for serial order in fifteen adults with a history of dyscalculia and a group of fifteen control subjects matched for age, education, IQ, and reading abilities. The participants were presented 6-letter sequences, and after a short delay, had to determine whether the serial order of two probe letters matched the order in the list. The dyscalculic group showed abnormally reduced activation in the right intraparietal cortex, and this specifically when judging letters from close serial positions, suggesting difficulties in processing fine grained ordinal information in STM. These findings demonstrate long-lasting alterations in neural networks associated with ordinal processing in STM for participants with dyscalculia and support the hypothesis of close links between serial order STM and numerical processing deficits.