Richards, J.E. (2002). Cortical sources of ERP for infants' recognition of briefly presented visual stimuli. Society for Psychophysiological Research, Washington D.C. (PDF)
Young infants show ERP component responses to briefly presented visual stimuli dependent on stimulus familiarity and probability. Some components (e.g., "Nc") represent simple orienting to the stimulus, whereas other components (late slow wave) are affected by recognition memory. This study examined these ERP components in infants from 20 to 32 weeks using high-density EEG recording to quantify cortical sources of these components.
Twenty infants were presented with a Sesame Street recording that was replaced with a familiar stimulus presented frequently ("FF"; 60% probability) or infrequently ("IF"; 20% probablity), and novel stimuli presented infrequently ("IN"; 20% probablity). Heart rate was used to assess the infant's attention to the Sesame Street recording at the time of the brief stimulus presentation (attentive or inattentive). EEG was recorded with a 124-channel system (EGI) and ERP averages were made from -50 ms to 2000 ms around stimulus onset. The ERP were quantified for each participant with spatial principal component (PC) analysis, clustered with other participant's PCs, and "equivalent current dipoles" were estimated for averaged PC loadings and individual participant loadings to locate cortical sources of the ERP components.
There were three findings. First, a spatial PC representing broad frontal-central negativity was active at about 500 ms following the brief stimulus presentation ("Nc" component). This activity was larger if the infant was in an attentive state. The size of the Nc component did not differ for the IN, IF, and FF stimuli. The cortical source of this component was located in the anterior cingulate gyrus (Brodmann area 33). Second, a PC reflecting scalp activity over the parietal scalp showed late slow wave activity (750 to 1600 ms). This cortical activity did not occur for the FF stimuli, was negatively activated for the IN stimuli and positively activated for the IF stimuli. It was present primarily on presentations in which the infant was attentive, but did occur to a lesser degree when the infant was inattentive but still fixating toward the monitor. The cortical source of this activity was the superior parietal lobe (Brodmann area 7). Third, at about the same time as the second component, there was a activation of a PC broadly spaced over central and parietal-central leads (800 to 1500 ms). This activity occurred only for the IN stimuli, and was unaffected by attention. Its cortical source was located in the posterior portion of the cingulate gyrus (Brodmann area 23). These results identify cortical sources of recognition memory activity in young infants. They suggest that the affect of attention is to enhance the cortical areas involved in "stimulus orienting" and those involved in recognition memory.