DEVELOPMENTAL THETA RESPONSE
125
the framework of the concept of the theta sys-
tem in the brain (Ba⅞ar, 1992), the strong
phase-locking is likely to result from stable (fa-
cilitated or traced) connections between neu-
ronal elements. Hence, it can be assumed that
the theta networks involved in responding dur-
ing the early stage (0-300 ms) of stimulus infor-
mation processing are stabilized or traced with
development in children so that repeatable
patterns can be produced at the central but not
at the frontal and parietal locations. The in-
crease in repeatability of the early theta re-
sponses is accompanied by a decrease in mag-
nitude, which might reflect a developmental
specialization of the theta networks based on
involving fewer but functionally defined ele-
ments (Courchesne, 1990). The large enhance-
ment factors in adults suggest that the neuronal
elements responding in the theta channel can
be coactivated (synchronized) simultaneously
by the external stimulus (Klimesch et al., 1994)
but no developmental changes were observed
for the enhancement of the theta responses.
With regard to the three single-sweep param-
eters analyzed here, it might be assumed that
the theta response system changes with devel-
opment in a way that enables less but function-
ally specified elements to be coactivated simul-
taneously under defined conditions. Reduction
of active elements, selection of networks, and
capability of synchronizing them upon stimu-
lation seem to follow differential time courses.
A ckno wledgments
Research was supported by the National Sci-
entific Research Fund at the Ministry of Edu-
cation, Science, and Technologies, Sofia,
Bulgaria, and the Deutsche Forschungsge-
meinschaft, Bonn, Germany (Contr. 436-BUL-
113/76).
We thank Dr. A. Vankov and Dr. T Demiralp
for software development, and V. Silyamova
for data processing. Special thanks are due to
Dr. John Polich for his support and most help-
ful comments.
Address correspondence to:
Dr. Vasil Kolev
Institute of Physiology
Bulgarian Academy of Sciences
Acad. G. Bonchev str., bl. 23
1113 Sofia
Bulgaria
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