Arabic digit processing in adults with mathematical learning disability.

The processing of Arabic digits is a core difficulty of children suffering from mathematical learning disability (MLD). Dominant accounts assume a semantic impairment affecting either the magnitude representation per se or its access from numerical symbols. But recent data have raised the hypothesis that the impaired processing of Arabic digits may be explained by a selective deficit of digit visual recognition (i.e., recognising a symbol as one of the digits, no matter its identity or numerical meaning). This study aims at testing whether the difficulty to process Arabic digits remains prevalent in adults with MLD and whether it is effectively associated with a digit visual recognition deficit. To do so, we compared 19 adults with MLD to 19 matched controls in an Arabic digit comparison task that required to identify the largest of two digits, and in an Arabic digit lexical decision task that required to decide whether a visual stimulus is a digit or not. The results showed that MLD participants took more time than control participants to perform the comparison task. In contrast, their performance in the digit lexical decision task was within the range of the control participants. Overall, this finding indicates that adults with MLD continue to experience difficulties to process the magnitude of Arabic digits efficiently, and this cannot be explained by a visual recognition deficit for Arabic digits. We conclude that their difficulties are best explained by an impaired representation of number magnitude or by an impaired access to this representation.

Subcortical hyperintensities are associated with cognitive decline in patients with mild cognitive impairment.

BACKGROUND AND PURPOSE: It has been suggested that subcortical lesions may influence cognitive performances at early stages of cognitive impairment but not in late stages of dementia. We aimed to test whether cognitive decline is associated with subcortical hyperintensities in patients with mild cognitive impairment (MCI). METHODS: We included 170 consecutive MCI patients (mean follow-up, 3.8+/-1.6 years). We assessed subcortical hyperintensities on a baseline magnetic resonance imaging scan with a semiquantitative rating scale. The mean annual cognitive decline was calculated with the Mini-Mental State Examination and the Dementia Rating Scale at baseline and the end of follow-up. RESULTS: Compared with patients whose cognitive performances remained stable or improved during follow-up, patients whose cognitive performances declined often had a larger amount (greater than the median of the distribution) of periventricular (PVH) (P=0.0005) and white-matter (P=0.02) hyperintensities. The rate of cognitive decline was higher with increasing PVH: mean change in the Mini-Mental State Examination score=0.16 vs -0.66 points/year in patients with PVH in the first versus third tertile (P=0.0002). The rate of decline in executive functioning was also higher with increasing PVH: mean change in the Dementia Rating Scale initiation subscore=-0.05 vs -1.42 points/year in patients with PVH in the first versus third tertile (P=0.04). These associations were independent of vascular risk factors, temporal lobe atrophy, and MCI subtype and were stronger in patients with baseline executive dysfunction. CONCLUSIONS: White-matter hyperintensities and especially PVH were significantly associated with cognitive decline in MCI patients. This result was independent of the MCI subtype but stronger in cases of executive dysfunction at baseline.

Prevalence of subcortical vascular lesions and association with executive function in mild cognitive impairment subtypes.

BACKGROUND AND PURPOSE: Subcortical hyperintensities (SH) have not been systematically evaluated in mild cognitive impairment (MCI). We sought to describe their frequency and distribution, and to test their association with cognitive characteristics in MCI patients. METHODS: We performed standardized neuropsychological tests and an MRI scan in 170 consecutive MCI patients. Medial temporal lobe atrophy and SH, including periventricular, lobar white matter, basal ganglia and infratentorial hyperintensities, were assessed with visual semiquantitative scales. RESULTS: The median age was 68.1 years (range: 45.5 to 87.0), and the median Mini-Mental State Examination score 28.0 (range: 26.0 to 30.0). MCI subtypes were amnestic single domain (21.2%), amnestic multiple domain (52.3%), nonamnestic single domain (21.8%), and nonamnestic multiple domain (4.7%). SH were found in 157 patients (92.6%); periventricular hyperintensities (80.6%) and lobar white matter hyperintensities (83.5%) were the most prominent locations. There was no association between SH and MCI subtypes. Executive dysfunction was independently associated with SH (odds ratio=2.53, 95% CI: 1.20 to 5.32), periventricular hyperintensities (odds ratio=2.51, 95% CI: 1.13 to 5.55), and white matter hyperintensities (odds ratio=2.08, 95% CI: 1.01 to 4.25). CONCLUSIONS: The prevalence of SH is high in MCI patients, irrespective of MCI subtypes. SH (especially periventricular hyperintensities, and lobar white matter hyperintensities) are associated with executive dysfunction.