Questioning the questions that have been asked about the infant brain using near-infrared spectroscopy

Abstract

Near-infrared spectroscopy (NIRS) is a noninvasive diffuse optical-imaging technique that can measure local metabolic demand in the surface of the cortex due to differential absorption of light by oxygenated and deoxygenated blood. Over the past decade, NIRS has become increasingly used as a complement to other neuroimaging techniques, such as electroencephalography (EEG), magnetoencephalography (MEG), and functional magnetic resonance imaging (fMRI), particularly in paediatric populations who cannot easily be tested using fMRI and MEG. In this review of empirical findings from human infants, ranging in age from birth to 12 months of age, a number of interpretive concerns are raised about what can be concluded from NIRS data. In addition, inconsistencies across studies are highlighted, and strategies are proposed for enhancing the reliability of NIRS data gathered from infants. Finally, a variety of new and promising advances in NIRS techniques are highlighted.

Keywords:

• Infancy
• Brain imaging
• Near-infrared spectroscopy

Acknowledgments

Preparation of this article was supported in part by grants from NIH (HD-37082) and the McDonnell Foundation (220020096) to the author, and from NSF (CBET-0931687) to Andrew Berger. Helpful comments on an earlier draft were provided by Andrew Berger, Mohinish Shukla, and two anonymous reviewers.

Notes

¹Direct measures of neural activity from surface electrodes on the scalp have been used with infants since the 1960s, but that voluminous literature is beyond the scope of the present review.

²Systemic vascular responses can be measured directly using a pulse oximeter, but recent evidence from adults suggests that regressing out these global responses only marginally improves the signal/noise of fMRI (Cooper, Gagnon, Goldenholz, Boas, & Greve, 2012).

³Note that this delayed HRF in infants could be the result, at least in part, of the contaminating effects of surface vascular signals. Minagawa-Kawai, van der Lely, et al. (2011) did not measure the adult HRF with NIRS to make a direct comparison with infants.

⁴The statistical tests of hemisphere differences for the two stimulus conditions do not appear to have been corrected for multiple comparisons. However, even a conservative Bonferroni correction would render the most significant p-value of <.0005 equal to <.025.

⁵Tsuzuki et al. (2007) provided evidence, in adults, that external skull landmarks provide a reasonable alternative to structural MRI data for transforming NIRS probe locations to MNI space.