The influence of the place-value structure of the Arabic number ...

Other areas associated with the fronto-parietal network
In general, activation in the intraparietal cortex extended to the adjacent extrastriate
cortex BA 19, bilaterally. Activation in the extrastriate cortex seems to be driven by top-down
processes originating from the intraparietal cortex. In particular, Weiss, Marshall, Zilles, and
Fink (2003) showed that parietal regions exerted top-down regulation over the activation in
the extrastriate cortex when visuo-spatial processing became more demanding. Such
activation of large portions of bilateral visual cortex accompanying the activation of the
intraparietal cortex in tasks involving number magnitude processing has been reported in
previous studies (Pinel et al., 2001; Wood et al., 2006). Another area activated in parallel with
the intraparietal cortex is the temporo-occipital area, also known as the visual number form
area (Cohen et al., 2002; Cohen et al., 2004). Activation in this region, mainly in the left
hemisphere, can be explained by more intensive processing of the visual identity of Arabic
digits in more complex triplets. Deeper visual processing was again required by the bisection
of large numerical ranges, by the computation of small distances to the mean, by nonmultiplicative
triplets, and by decade crossing.
Finally, the prefrontal area activated in contrasts demanding deeper magnitude
processing in the present study overlapped with those regions that Doricchi et al. (2005)
associated with the deficit in numerical bisection performance of hemineglect patients. The
patients examined by Doricchi, Guariglia, Gasparini, and Tomaiuolo (2005) had more
pronounced lesions in the prefrontal cortex than other hemineglect patients. Additionally they
were also more impaired in a task of spatial working memory. Thereby, the activation in the
dorsolateral prefrontal cortex observed in the NBT may be attributed to spatial working
memory processes necessary for bisecting numerical intervals.
In sum, items that are more complex led to increased magnitude processing in the
intraparietal cortex. Moreover, via top-down regulation, this activation also spread into the
posterior superior parietal lobule as well as other areas subserving visuo-spatial processes.
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