Neuropsychologia 2010 Jan;48(1):278-87
Cerebral Function Unit, Greater Manchester Neuroscience Centre, Salford Royal Foundation Trust, Salford, UK.
Arithmetic skills are generally claimed to be preserved in semantic dementia (SD), suggesting functional independence of arithmetic knowledge from other aspects of semantic memory. However, in a recent case series analysis we showed that arithmetic performance in SD is not entirely normal. The finding of a direct association between severity of patients' semantic disorder and arithmetic impairment pointed to a closer relationship between semantic memory and arithmetic knowledge than previously acknowledged. The present study aimed to determine whether arithmetic performance in SD is subject to the same influences as has been found in other semantic domains, namely an autobiographical effect. SD patients were assessed on their ability to perform arithmetic in personally relevant compared to non-personal contexts. Patients who were regular, current followers of the television game show Countdown performed better on a simplified version of the show's number game compared to a conventional written calculation task, whereas patients with no experience of Countdown demonstrated the opposite pattern. SD patients showed better knowledge of multiplication table 'facts' when these were embedded in a situation relevant to their daily lives compared to a non-personal arithmetic task. They also performed better on a written calculation task when problems were presented as a monetary transaction compared to a standard arithmetic problem. A reference group of patients with Alzheimer's disease (AD) showed the reverse pattern. The findings provide convincing evidence that autobiographical relevance influences SD patients' arithmetic performance. Moreover, they challenge current views on conceptual number knowledge as a unitary, abstract competence.