Despite a common belief that a high-density EEG montage (i.e., more than 100 channels) is required to reliably compute CSD estimates, given previous findings highlighting problems with spatial aliasing for the interpretation of undersampled CSD estimates (Junghöfer et al., 1997; Srinivasan et al., 1998), low-density CSD estimates (i.e., 31 channels) can not only improve ERP data analysis and interpretation, but are also surprisingly accurate and reliable for a group of subjects. Because averaging individual CSD topographies across subjects effectively applies a spatial low pass filter to the data, the resulting spatially-smoothed CSD group topographies are sufficiently represented by fewer recording sites, revealing effectively identical estimates at these sites when compared with CSDs obtained from high-density (i.e., 129-channel) ERPs (Kayser and Tenke, 2006b). Therefore, when group findings are the primary research objective, low-resolution CSD topographies can be as efficient as their high-density counterparts, and have been useful in studying long-lasting ERP components during working memory in schizophrenia (Kayser et al., 2006), disentangling overlapping P3 generators in depression (Tenke et al., 2008), and clarifying stimulus- and response-related neuronal generator contributions to ERP old/new effects during auditory and visual word recognition memory (Kayser et al., 2007).
