Using near-infrared spectroscopy to assess neural activation during object processing in infants

Abstract

The capacity to represent the world in terms of numerically distinct objects (i.e., object individuation) is a milestone in early cognitive development and forms the foundation for more complex thought and behavior. Over the past 10 to 15 yr, infant researchers have expended a great deal of effort to identify the origins and development of this capacity. In contrast, relatively little is known about the neural mechanisms that underlie the ability to individuate objects, in large part because there are a limited number of noninvasive techniques available to measure brain functioning in human infants. Recent research suggests that near-IR spectroscopy (NIRS), an optical imaging technique that uses relative changes in total hemoglobin concentration and oxygenation as an indicator of neural activation, may be a viable procedure for assessing the relation between object processing and brain function in human infants. We examine the extent to which increased neural activation, as measured by NIRS, could be observed in two neural areas known to be involved in object processing, the primary visual cortex and the inferior temporal cortex, during an object processing task. Infants aged 6.5 months are presented with a visual event in which two featurally distinct objects emerge successively to opposite sides of an occluder and neuroimaging data are collected. As predicted, increased neural activation is observed in both the primary visual and inferior cortex during the visual event, suggesting that these neural areas support object processing in the young infant. The outcome has important implications for research in cognitive development, developmental neuroscience, and optical imaging.

Fig. 1

Narrow- and wide-screen test events from Wilcox and Baillargeon. Steps 1 to 4 were repeated until the end of the trial. The ball and box varied on many feature dimensions, including shape, color, and texture.

Fig. 2

Raw data (left column) and block-averaged response over four trials from a single subject illustrate the importance of filtering the spatial covariance of the data with a PCA to reduce motion artifacts in the data. The raw data from the primary visual cortex is displayed in optical density units at 690 and 830 nm over the 300-s duration of the experiment. The initiation of each 30-s trial is indicated by the thick vertical bar. The block-averaged data are displayed in relative concentration units of HbO₂ and HbR. The first row shows the raw data. The subsequent rows show the effect of filtering one, three, and four principle components.

Fig. 3

Mean change in HbO₂, HbR, and HbT in response to the wide-screen ball-box event, in relative units (y axis). The 45-s trial epoch (see text) is displayed in the following way: −5 to 0 is baseline, 1 to 30 s is the 30-s ball-box event, and 31 to 40 s is poststimulus. Relative changes in HbO₂, HbR, and HbT during the time 10 to 30 s of this epoch were compared to 0. All observed changes were significant (p < 0.01).