Prefrontal Cortex Involvement in Processing Incorrect Arithmetic Equations

Introduction

Brain imaging studies have identified a distributed network involved in arithmetic reasoning: the lateral and ventral prefrontal cortex, posterior parietal lobe, and subcortical regions including the caudate nucleus and cerebellum.

Electrophysiological studies show processing incorrect equations (but not correct equations) elicits prominent event-related potentials (ERP).

Method

We studied the neural substrates of this process using fMRI during processing correct and incorrect equations: 16 healthy adolescents and adults (8 M/8F, 16-23 years) were provided easy (2 operand, a+b=c) and difficult (3 operand, a+b-c=d) equations with control epochs of visually presented numbers.

Results 1

Activation during processing of incorrect, compared to correct, equations: coronal sections (left), surface rendering (below).

Incorrect vs. Correct

Activation limited to:

L dorsolateral and ventrolateral prefrontal cortex (BA 9/46 and 47).

Results 2

Overlaps between areas during processing incorrect vs. correct equations (yellow/red, left) and correct vs. incorrect equations compared to control condition (cyan, below).

DLPFC in middle frontal gyrus shows activation overlap between 2 analyses (yellow circles).

VLPFC in inferior frontal gyrus activated only during differential processing of incorrect equations (green circles).

Overlaps between areas during processing Correct vs. Incorrect equations compared to control condition.

Surface rendering showing activation during 3-operand vs. 2-operand equations: activity limited to right angular gyrus/intra-parietal sulcus.

Conclusions

The DLPFC region differentially activated by incorrect equations was also involved in overall arithmetic processing, whereas the VLPFC was activated only during the differential processing of incorrect equations.

Differential response to correct and incorrect arithmetic equations was not observed in parietal cortex regions such as the angular gyrus and intra-parietal sulcus, areas known to play a specific role in processing arithmetic computations.

The pattern of brain response seen in this study is consistent with the hypothesis that processing incorrect equations involves detection of an incorrect answer and resolution of interference between the internally computed and externally presented incorrect answer.

That is, the greater activation during processing of incorrect equations may reflect additional operations involved in maintaining the results in working memory, while subjects attempt to resolve the conflict and select a response.

Menon V, Mackenzie K, Rivera SM, Reiss AL. (2002). "Prefrontal Cortex Involvement in Processing Incorrect Arithmetic Equations: Evidence from Event-Related fMRI." Hum Brain Mapp 16, 119-130.  Abstract - PDF