Mapping the Brain for Math – Reversible inactivation by direct cortical electrostimulation and transcranial stimulation

Salillas, E., Semenza, C., (In Press) Mapping the Brain for Math. Reversible inactivation by direct cortical electrostimulation and transcranial magnetic stimulation. In Cohen Kadosh R. & Dowker A. (Eds.), Oxford Handbook of Numerical Cognition. New York: Oxford University Press.

Abstract

Invasive cortical electro-stimulation, such as direct cortical electrostimulation (DCE), and non-invasive brain stimulation, such as transcranial magnetic stimulation (TMS), allow for the brain mapping in the search of areas that are crucial for a given function. Here, we describe the research that has been conducted on number cognition using these techniques, as well as attempt to contrast the findings between and within them. The results are not always fully convergent with correlational data from neuroimaging. Various TMS studies have targeted parietal areas to find critical areas for quantity representation, links between space and numbers, and possible overlaps or dissociations between numerical and non-numerical quantity or finger gnosis, while others have focused on calculation. Attending to TMS data, the intraparietal sulcus and surrounding areas in the left and right hemisphere seem crucial for quantity processing, although a higher amount of findings point to a left hemisphere predominance in number semantics. The few works addressing calculation suggest that bilateral parietal areas are essential. TMS studies also show a bilateral parietal basis in the link between number and space and have extended the areas of study to frontal and most posterior  parietal sites. All DCE studies to date have used calculation tasks, with the ultimate goal of preserving critical functions during surgery. DCE has been delivered mainly to the dominant hemisphere finding both dissociation and overlap between operations. Only a few studies have investigated the right hemisphere for calculation. We propose an integrative view of positive findings and focus on convergence and possible improvement options. Although regularities are found between these techniques in the area of calculation, more research is needed before arriving at conclusions that will have not only basic, but also extensive, clinical importance.

Keywords: TMS, DCE, parietal lobe, numerical representation, calculation.

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