Using optical imaging to investigate functional cortical activity in human infants

Imaging methods have caused a revolution in cognitive science for research on adult brain function. It is clear that many of these neuroscience methods can be applied to younger populations to investigate the relationship between cognition and brain development. The goal of this chapter is to describe the feasibility of using optical imaging on human infants. The motivation for using neuroimaging techniques on young populations is that they allow us to address critical issues of continuity and change over development. When a young infant, an older child, and an adult all exhibit a behavioral discrimination, how can we tell whether the underlying mechanisms producing the discrimination are the same (a case of developmental continuity) or different (a case of qualitative developmental change)? Imaging studies of infants, combined with and guided by the findings of imaging studies with adults and by behavioral studies, should let us approach this question. If we see convergent findings in infants and adults at both the behavioral level and the neural level, we can infer continuity across development. Conversely, non-convergence between infants and adults may signal points of significant developmental change, as well as providing a window for examining such change. Imaging tasks allow us to test young infants in a state of full attention. These same tasks have been used with great success in fMRI with adults using freeviewing, providing opportunities of comparisons across tasks. However, fMRI techniques with infant participants are challenging because infants lack the ability to remain still while awake. With near-infrared spectroscopy (NIRS), the infant is allowed to move with some degree of freedom and they are tested while sitting upright on their caretakers lap. The vast majority of neuroscience research on infants has been done with ERP (Gliga and Dehaene-Lambertz 2007; Kuhl 2004; Nelson and Monk 2001; Neville 2005), and so comparisons to fMRI research are indirect and spatial localization for neural activity is minimal. Using optical imaging on infants provides a window to the characteristics of the hemodynamic response associated with functional activity. These data will allow for more direct comparisons with fMRI studies on adults and children. For this reason optical imaging holds promise as a technique for elucidating the links between behavioral and neural development. In this chapter, we will discuss the feasibility of one type of optical imaging called NIRS as a tool for cognitive scientists who study development. We will describe the technology, review existing studies using NIRS on infants, and speculate about how NIRS technology will impact the emerging field of developmental cognitive neuroscience.