Developmental Changes in ERPs

To date, much of what is known about the development of ERPs elicited by visual stimuli has been derived from studies of memory development in children less than a year old (for a recent, comprehensive review of this area, see DeBoer, Scott, & Nelson, 2004). In general, there are three broad ERP characteristics that change with development: (1) peak amplitude, (2) latency, and (3) the actual morphology (shape) of the waveforms and the types of waveforms that are manifested.

Overall, there is a decrease in the latency of the peaks of ERP waveforms with development. (see Figs. 3.2A through 3.2D). Often, as in the case of Nc, there is a rapid change in latency of the waveform peak in the first year of life. Webb et al. (2005), in a longitudinal investigation of the development of ERP waveforms from 4 months to 12 months of age in a recognition memory paradigm, showed that the most significant latency decreases for Nc occurred from 4 to 8 months. This decreased latency is almost certainly brought about by normative brain maturational processes, such as increased myelination and refinement of synapses, that result in decreases in processing speed. This phenomenon is illustrated in Figure 3.2, where the latency of the Nc waveform is elicited by identical experimental paradigms whereby a face is passively viewed, across samples of children at 6 months, 15 months, 30 months, and 45 months of age. As can be seen, the mean latency of Nc decreases by 126 ms across 39 months.

Cross-sectional studies have examined the development of the P300 evoked by visual stimuli. This waveform has not been observed in children younger than 4 years of age. However, to date, no longitudinal studies have documented the development of this waveform, and thus it is unknown exactly when, how, and under what experimental circumstances this waveform appears. Nelson and colleagues have made the convincing theoretical argument that the infant PSW is the precursor to the later-observed P300 (e.g., Nelson, 1994). Examining the development of ERP waveforms in children who have experienced maltreatment, given the probable association of changes in ERP waveform latency and morphology with development of the neural substrate, would potentially provide valuable information concerning the effects of maltreatment on the developing brain.

One important caveat in interpreting developmental ERP studies of infants and children is that, to date, with the exception of Webb et al. (2005), they are cross-sectional, typically comparing ERP waveforms among groups of individuals of different ages. In addition, many of the paradigms used in studying ERP waveforms in adults and school-aged children have involved active-task responses (e.g., pressing a button when a "target" stimulus is presented), while, of necessity, ERP studies of infants and young children have employed passive viewing paradigms (i.e., the infant simply looks at stimuli). Interestingly, some studies (e.g., Nelson et al., 1998) have compared adult ERPs in passive and active paradigms,

figure 3.2. (From top) (A) Event-related potential (ERP) data (grand mean) from a sample of 6-month-old infants elicited while viewing face stimuli. (B) ERP data (grand mean) from a sample of 15-month-old infants elicited while viewing face stimuli. (C) ERP data (grand mean) from a sample of 30-month-old children elicited while viewing face stimuli. (D) ERP data (grand mean) from a sample of 45-month-old children elicited while viewing face stimuli. For all plots, data is from the Cz electrode (midline central scalp region), the vertical axis is amplitude is in microvolts, and the horizontal axis is time in milliseconds.

figure 3.2. (From top) (A) Event-related potential (ERP) data (grand mean) from a sample of 6-month-old infants elicited while viewing face stimuli. (B) ERP data (grand mean) from a sample of 15-month-old infants elicited while viewing face stimuli. (C) ERP data (grand mean) from a sample of 30-month-old children elicited while viewing face stimuli. (D) ERP data (grand mean) from a sample of 45-month-old children elicited while viewing face stimuli. For all plots, data is from the Cz electrode (midline central scalp region), the vertical axis is amplitude is in microvolts, and the horizontal axis is time in milliseconds.

with both conditions eliciting P300 waveforms, with the active condition eliciting a greater-amplitude P300.

The next section of this chapter, following a brief review of the effects of maltreatment on the development of socioemotional and neuro-behavioral functioning, will critically examine the few existing studies of ERPs in children reared in atypical emotional environments. Although these studies have not employed ERPs to directly examine memory functioning in these at-risk children, they do provide some insight into the potential usefulness of ERP methodology for elucidating the association of maltreatment with memory deficits.

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