Richards, J.E. (2004). A quantitative method to use high-density EEG recordings to localize cortical sources of infant cognitive activity. International Society for Infancy Studies, Chicago, IL.
Many models of infant cognitive development hypothesize that changes in cognition (attention, memory, face processing, language) are based upon the development of specific neural systems. Such cognitive neuroscience models have been tested in adults and older children with neuroimaging techniques such as PET and fMRI. However, the application of such techniques to infant participants is either unethical (e.g., PET) or impractical (e.g., fMRI). An alternative to such neuroimaging techniques is the use of high-density EEG recording and cortical source analysis. The current poster will overview a method being developed for such analyses with infant participants.
The method consists of four steps: 1) recording of EEG activity with high-density (64- or 128-channel) EEG system. The use of the high-density EEG / ERP gives the resolution necessary to localize cortical sources of ERP activity. 2) analysis of individual participant raw segmented data with independent components analysis (ICA) or principal components analysis (PCA). The raw segmented data is analyzed rather than ERP averages, allowing the separation of cortical sources by experimental factors later in the analysis. The component analysis results in loadings that represent topographically-organized scalp sources. These scalp sources, particularly those from ICA, contain any single-source components generating the EEG. 3) identification of clusters of components with similar topographical loadings; 4) estimation of equivalent current dipole (ECD), i.e., cortical location. The ECD estimation is done on the components coming from individual participants, and are seeded by an ECD from the grand average of the cluster groups. 5) calculation of component activations in relation to experimental factors. whose loadings may be used to acquire single-source ECD models. The activations of the clustered component groups shows the experimental validity of the cortical sources identified in the ICA.
This technique has been applied to cortical sources involved in infant spatial cueing, infant visual recognition memory, and the responses of young infants to face-stimuli. For example, the cortical source of the P1 validity effect in young infants during a spatial cueing task was shown to be located in the extrastriate occipital cortex and ventral fusiform gyrus. The “Nc” component occurring in response to the presentation of a brief visual stimulus had its cortical source in the prefrontal cortex, including the anterior cingulate. These results show that scalp-recorded EEG/ERP may help identify brain areas involved in infants’ cognitive development. The application of the high-density EEG recording and the methods for cortical source localization give researchers a tool to verify neurodevelopmental models of infant development.