Near-infrared spectroscopy shows right parietal specialization for number in pre-verbal infants

Abstract

Bilateral regions of the intraparietal sulcus (IPS) appear to be functionally selective for both rudimentary non-symbolic number tasks and higher-level symbolic number tasks in adults and older children. Furthermore, the ability to mentally represent and manipulate approximate non-symbolic numerical quantities is present from birth. These factors leave open whether the specialization of the IPS develops through the experience of learning a symbolic number system or if it is already specialized before symbolic number acquisition. Using the newly emerging technique of functional Near-Infrared Spectroscopy (fNIRS) over left and right parietal and lateral occipital regions, we show right parietal specialization for number in 6-month-old infants. These results extend the current literature in three ways: by successfully implementing an event-related NIRS design in infants, by showing parietal specialization for number occurs before the acquisition of language, and by suggesting number representation may be initially right lateralized and becomes bilateral through experience.

Conflict of interest statement

We declare no competing financial interests between authors.

Copyright 2010 Elsevier Inc. All rights reserved.

Figures

Figure 1

Schematic of optical probe and placement in reference to the international 10–20 EEG system. (A). Lateral view of the 10–20 measurements and superimposed probe placement. The red circle represents the light emitter and the blue squares represent the light detectors. (B). Top view of 10–20 system and superimposed probe placement. (C). Schematic representation of the probe including distances between light emitters and detectors.

Figure 2

Summary of fNIRS results for number and shape changes. (A). Hemodynamic response observed for number changes from 2 seconds before to 8 seconds after deviant image onset. The “*” indicates a significant difference from baseline (p

Figure 3

Relative OxyHb response for number changes and shape changes at right occipital and parietal sites. Y axis reflects relative change in oxygenated hemoglobin concentration (micromolars) relative to baseline. The “*” indicates statistical significance (p