Developmental changes in the event-related EEG theta response and P300 Juliana Yordanova*, Vasil Kolev Institute of Physiology, Bulgarian Academy of Sciences, Acad. G. Bonchev str., bl. 23, 1113 Sofia, Bulgaria Accepted for publication: 8 May 1997 Abstract Event-related potentials (ERPs) from 50 children (6–11 years) and 10 adults were elicited by auditory passive, and by rare target and frequent non-target stimuli, and analyzed in the time and frequency domains. The latency of the maximal theta response (or the theta frequency component of the ERP) was evaluated with respect to age and scalp topography effects. The major findings were: (1) The latency of the maximal theta response decreased with increasing age in children, although for each stimulus type and location adults had shorter latencies than the children. (2) The developmental time course of latency reduction depended on the electrode location, with the most prominent reduction occurring at 8 years at Cz, and no differences between children groups obtained for the frontal site. (3) Maximal theta response latency was strongly associated with the latency of the late parietal P400–700 (P3b) component in children. The results suggest that the developmental latency decrease in P300 processes originate from a decrease in the preceding theta-related processes and may reflect a speeding of cognitive stimulus evaluation.  1997 Elsevier Science Ireland Ltd. Keywords: Children; Event-related potentials; Theta response; P300-wave 1. Introduction In addition to time domain analysis, frequency domain analysis can be an informative way for studying event- related electroencephalographic (EEG) activity. After exter- nal stimulation, functionally meaningful oscillatory EEG responses in different frequency bands (delta, theta, alpha, gamma) have been recorded from the brain (Bas ¸ar and Bul- lock, 1992; Pantev et al., 1994; Bas ¸ar et al., 1997). These EEG responses have been proposed to originate from the event-related reorganization of the ongoing (spontaneous) EEG as revealed by the frequency stabilization, time- or phase-locking to stimulus, and amplitude enhancement or damping of the post-stimulus EEG (Davis, 1973; Sayers et al., 1974; Bas ¸ar, 1980, 1992; Parvin et al., 1980). Within this view, event-related oscillatory potentials strongly depend on the spontaneous EEG activity. Developmental studies have found that the frequency content of the spontaneous EEG undergoes significant alterations with increasing age in children (Peterse ´n and Eeg-Olofsson, 1971; Matous ˇek and Peterse ´n, 1973; Nieder- meyer, 1993): The frequencies of the dominant spectral components increase (Katada et al., 1981), while the abso- lute and relative power of the EEG in the slower (delta and theta) frequency bands decrease with age (Matthis et al., 1980; John et al., 1980; Gasser et al., 1988). Given these natural changes in spontaneous EEG rhythms from child- hood to adulthood, as well as the likely functional signifi- cance of evoked oscillations, the analysis of event-related frequency responses of the EEG in children might provide an useful physiological approach to study developmental variations in the processes of stimulus information proces- sing. In view of functional significance, the EEG theta band (4–7 Hz) activity of adults has been consistently correlated with higher cognitive and associative brain processes like arithmetic operations, mental rotation, concept learning, etc. (Mizuki et al., 1980, 1983; Lang et al., 1989; Inouye et al., 1994). Likewise, the stimulus-related EEG theta response, defined as the 4–7 Hz frequency component of the event- related brain potentials (ERPs), also has been correlated with cognitive brain operations: Major results from aver- aged potentials have suggested that the phase-locked theta band component of the ERP reflects processes of focused Electroencephalography and clinical Neurophysiology 104 (1997) 418–430 0168-5597/97/$17.00  1997 Elsevier Science Ireland Ltd. All rights reserved PII S0168-5597(97)00054-3 EEP 96687 * Corresponding author. Tel./fax: +35 92 738469; e-mail: jyord@iph.bio.acad.bg