The neural correlates of mental arithmetic in adolescents: a longitudinal fNIRS study

Abstract

Background: Arithmetic processing in adults is known to rely on a frontal-parietal network. However, neurocognitive research focusing on the neural and behavioral correlates of arithmetic development has been scarce, even though the acquisition of arithmetic skills is accompanied by changes within the fronto-parietal network of the developing brain. Furthermore, experimental procedures are typically adjusted to constraints of functional magnetic resonance imaging, which may not reflect natural settings in which children and adolescents actually perform arithmetic. Therefore, we investigated the longitudinal neurocognitive development of processes involved in performing the four basic arithmetic operations in 19 adolescents. By using functional near-infrared spectroscopy, we were able to use an ecologically valid task, i.e., a written production paradigm.

Results: A common pattern of activation in the bilateral fronto-parietal network for arithmetic processing was found for all basic arithmetic operations. Moreover, evidence was obtained for decreasing activation during subtraction over the course of 1 year in middle and inferior frontal gyri, and increased activation during addition and multiplication in angular and middle temporal gyri. In the self-paced block design, parietal activation in multiplication and left angular and temporal activation in addition were observed to be higher for simple than for complex blocks, reflecting an inverse effect of arithmetic complexity.

Conclusions: In general, the findings suggest that the brain network for arithmetic processing is already established in 12-14 year-old adolescents, but still undergoes developmental changes.

Keywords: Adolescents; Arithmetic complexity; Functional near-infrared spectroscopy (fNIRS); Longitudinal development; Mental arithmetic; Natural setting.

Fig. 1

a Positions of the fNIRS channels mapped on the brain (by Minako Uga). As an example, the right brain hemisphere is shown along with the red marked positions for the orientation of the probeset (the same applies to the left hemisphere). Channels included in the parietal, frontal, and parieto-temporal ROIs are marked by the orange boxes. b Example trial for the arithmetic task. The adolescents had to produce the correct solution and write it on the screen. c Exemplary course of the fNIRS signal. The block average curves of O₂Hb (red), HHb (blue) and signal corrected by CBSI (orange) are given for the left parietal ROI for simple subtraction in grade 7

Fig. 2

Number of presented trials in the a addition, b subtraction, c multiplication, and d division tasks. Significant arithmetic complexity and grade effects are marked (*p < .05). Error bars indicate 1 SE of M

Fig. 3

Cortical activation in the frontal and parietal ROIs. a Significant reduction in frontal activation from grade 6 to grade 7 in the subtraction task (*p < .05). b Significantly increased parietal activation for simple compared to complex blocks in the multiplication task (*p < .05). Error bars indicate 1 SE of M

Fig. 4

Cortical activation in the parieto-temporal ROIs. a Significant change in parieto-temporal activation from grade 6 to grade 7 in the addition task (*p < .05). b Significantly increased left parieto-temporal activation for simple compared to complex blocks in the addition task (*p < .05). c Significant change in parieto-temporal activation from grade 6 to grade 7 in the multiplication task (*p < .05). Error bars indicate 1 SE of M