fNIRS in the developmental sciences

Abstract

With the introduction of functional near-infrared spectroscopy (fNIRS) into the experimental setting, developmental scientists have, for the first time, the capacity to investigate the functional activation of the infant brain in awake, engaged participants. The advantages of fNIRS clearly outweigh the limitations, and a description of how this technology is implemented in infant populations is provided. Most fNIRS research falls into one of three content domains: object processing, processing of biologically and socially relevant information, and language development. Within these domains, there are ongoing debates about the origins and development of human knowledge, making early neuroimaging particularly advantageous. The use of fNIRS has allowed investigators to begin to identify the localization of early object, social, and linguistic knowledge in the immature brain and the ways in which this changes with time and experience. In addition, there is a small but growing body of research that provides insight into the neural mechanisms that support and facilitate learning during the first year of life. At the same time, as with any emerging field, there are limitations to the conclusions that can be drawn on the basis of current findings. We offer suggestions as to how to optimize the use of this technology to answer questions of theoretical and practical importance to developmental scientists.

FIGURE 1

Mean change in HbO, HbR, and HbT in the primary visual cortex in response to a visual event. (Reprinted with permission from Wilcox et al.). The visual event was an occlusion sequence involving a green dotted ball and a red studded box. On the y-axis are relative optical density units and on the x-axis is time: −5 to 0 is the pre-stimulus baseline, 1–30 seconds is the visual event, and 31–40 seconds is the post-stimulus baseline. Relative changes in HbO, HbR, and HbT, averaged over 10–30 seconds of the test trial, were compared to 0. All responses (HbO, HbR, and HbT) differed significantly from 0 (P < .01)

FIGURE 2

The shape difference, color difference, and control test events of Wilcox et al. Each cycle of the test event was 10 seconds and infants saw two complete cycles during each test trial. These events were presented live in a puppet stage apparatus. During the baseline interval, a curtain was lowered over the opening of the apparatus and infants received no auditory or visual stimulation.

FIGURE 3

The headgear used by Wilcox et al. (a) Configuration of the emitters (red circles) and detectors (black squares), and the nine measurement channels, in the headgear. Emitters were placed relative to 10–20 coordinates of the International 10–20 system (Figure 4). All the emitter-detector distances were 2 cm. Each detector read from a single emitter except for the detector between T3 and T5, which read from both emitters. The light was frequency modulated to prevent ‘cross-talk’. O1 lay over occipital cortex, T5 over posterior temporal cortex, T3 over anterior temporal cortex, and P3 over posterior parietal cortex. (b) Infants sat in a supportive seat to restrain excess movement. An elasticized headband was slid onto the infant’s head and secured by a chinstrap.

FIGURE 4

The International 10–20 system for electrode placement projected onto a schematic of an infant’s head.

FIGURE 5

Lateral view of the adult human brain (Greys Anatomy 726) with cortical areas labeled. Approximate locations of the lateral occipital complex (LOC) and occipital face area (OFA) are displayed. The fusiform face area (FFA) is located underneath the surface of the cortex, hence cannot be viewed here or investigated using fNIRS. The superior temporal sulcus is highlighted in red and the Sylvian fissure (or lateral sulcus) is highlighted in yellow.

FIGURE 6

The speed-discontinuity, path-discontinuity, and control test events of Wilcox et al. Each cycle of the test event was 12 seconds and infants saw two complete cycles during each test trial. These events were presented live in a puppet stage apparatus. During the baseline interval, a curtain was lowered over the opening of the apparatus and infants received no auditory or visual stimulation.

FIGURE 7

Figure 1 (a and b) Examples of the face and object stimuli used by Otsuka et al. (c) Location of the optical fibers placed in each hemisphere. The distance between the fibers was 2 cm. T3 and T4 were located at the center between channels 11 and 12 and 23 and 24, respectively. (d) An infant wearing the headgear during the experimental session. (Reprinted with permission from Ref . Copyright 2006 Elsevier)

FIGURE 8

(a) An example of the dynamic biological and mechanical test stimuli, and the static baseline stimuli, of Lloyd-Fox et al. (b) A schematic view of the headgear configuration with the approximate location of the channels shown in relation to the International 10–20 system. (Reprinted with permission from Ref . Copyright 2009 John Wiley & Sons)

FIGURE 9

Still frames from the dynamic face stimuli used by Grossman et al. Gender, age, and orientation of the face were randomly varied and counterbalanced. In the mutual gaze condition (upper half), the person’s eyes moved toward the infant, and in the averted gaze condition (lower half), the person’s eyes moved away from the infant. The eyebrow-raised and closed-mouth smiles were identical in the two conditions. (Reprinted with permission from Ref . Copyright 2008 Royal Society)

FIGURE 10

Details of the procedure used by Gervain et al. (a) The experiments’ design. The upper boxcar shows how the consecutive stimulation blocks unfold. The lower boxcar indicates the sequence of sentence types within a block. (b) The placement of the probes overlaid on a schematic neonate brain. Although individual variation cannot be excluded, this placement ensured recording from perisylvian and anterior brain regions. The dashed white lines separate anterior and posterior ROIs. The red ellipses indicate the channels included in the frontal area of interest (LH: channels 2 and 5; RH: channels 13 and 15). The blue ellipses indicate channels included in the temporal area of interest (LH: channels 3 and 6; RH: channels 17 and 19). (Reprinted with permission from Ref . Copyright 2008 National Academy of Sciences).