Developmental Dyscalculia is a maths learning disorder that affects roughly 3-6% of the population. To learn more about the basics of what it is, see our previous article What is Dyscalculia: Why Some Kids Struggle with Maths While Doing Well at Other Subjects. In this article we are going to discuss its potential causes.
What Is the Specific Brain Impairment that Causes Developmental Dyscalculia?
The short answer is that we are not sure yet. There could be one core deficit in the brain that underlies Developmental Dyscalculia or there could be several. Perhaps the most predominant theory in the neuroscientific literature is that dyscalculia results from impairment of the Approximate Number System (ANS; Piazza et al., 2010). The ANS equips humans with the capacity to quickly and instinctively understand, estimate and manipulate non-symbolic (i.e. not based on the symbolic number system 1, 2, 3 etc.) quantities.
A corresponding theory suggests that dyscalculia impairment is not linked to the ANS per se, but that dyscalculics’ ability to automatically map symbols to their corresponding magnitudes is disrupted (De Smedt & Gilmore, 2011; Rousselle & Noël, 2007) . To provide an example: a typically developing child would be able to see four dots and correctly identify that with the numerical symbol 4. However, a child with dyscalculia would likely have difficulty with such a task. According to this theory, such difficulty arises not because the child is unable to perceive that there are four dots present, but because he/she is unable to map this quantity to the correct numerical symbol of “4”.
However, emerging from the finding that numerous cognitive functions and skills may be disrupted in dyscalculia, several alternative theories have been proposed. Firstly, numerous studies have found disrupted verbal and/or visuo-spatial working memory functions in dyscalculics (link to Page 2i) (e.g. Keeler and Swanson, 2001; Bull et al., 2008; Swanson, 2006; Geary, 2004). Support for this supposition is strong with several studies indicating the importance of working memory (in particular, visuo-spatial working memory) in mathematical processing, including work done within the CNE maths group itself (link to maths and memory page). Secondly and closely linked to these visuo-spatial working memory deficiencies, some studies have reported spatial processing difficulties in developmental dyscalculia (Rourke and Conway, 1997; Rourke, 1993). Spatial processing is likely to be critical in mathematical computations which involve some form of visualisation such as imagining operations along a mental number line. Thirdly, disruptions to the central executive system have been implicated in dyscalculia. For instance, researchers have revealed a link between mathematical development and inhibitory function and more crucially, that such inhibitory function may be deficient in dyscalculia (Blair and Razza, 2007; Bull and Scerif, 2011; Bull et al., 1999; Espy et al., 2004; McKenzie et al., 2003; Pasolunghi et al., 1999; Pasolunghi and Siegel, 2004; Swanson, 2011). Similar results have been revealed with regards to attentional function (Swanson, 2011; Ashkenazi et al., 2009; Hannula et al., 2010). Central executive processes drive the working memory system by coordinating and controlling “online” information. Such processes are likely to be central to mathematical computations which require the continuous selection and manipulation of several items and processing steps. It is therefore highly plausible that disruption to such central executive functions might result in mathematical difficulties.
Overall, there is substantial evidence to suggest that there is no unique functional impairment at the heart of developmental dyscalculia, but that several cognitive functions may be implicated. Consequently, at the CNE maths group we adopt a multi-computational view of dyscalculia; rather than focusing on the search for a unitary underlying cause of dyscalculia, we aim to identity whether the condition can be related to individual variability in specified components of several cognitive functions such as memory and attentional processes.
Our lab, as well as many others throughout the world, are working very hard on this problem so that Jenny and other children like her can get the best education possible.