Developmental changes in the theta response system: a single sweep analysis



DEVELOPMENTAL THETA RESPONSE

119


(a)                  (b)                    (c)





TIME (ms)


Figure 4 (a) Averaged ERPs fil-
tered in the theta (4-7 Hz) range,
(b) superimposed single sweeps fil-
tered in the same (4-7 Hz) range,
and (c) the corresponding SSWI
histograms for six representative
subjects at 6,7,8,9, and 10 years of
age, and an adult. Children had larg-
er single theta responses than
adults, especially in the late time
window (300-600 ms). As reflected
in the SSWI histograms, children
also displayed a weaker phase-lock-
ing in both the early and late time
windows than adults. All recordings
are from the passive Ustening con-
dition at Cz. Along the Y-axes - am-
plitude (μV) for (a) and (b), and
number of synchronized single
waves for (c).


wave P400-700 that occurred primarily in re-
sponse to the targets and decreased in latency
with advancing age in children. A detailed
analysis of the time-domain ERP components
has been reported elsewhere (Yordanova, An-
gelov, Silyamova, & Kolev, 1992).

Theta activity analysis

Prestimulus theta power

The values of the absolute theta power of the
EEG preceding the passive, target, and nontar-
get ERPs were first subjected to age x stimu-
lus × electrode analysis of variance. No sig-
nificant main effect or interactions of stimulus
were obtained. The significant effect of age
found for each stimulus type resulted from the
gradual decrease in theta power between 6 and
10 years, with the lowest values manifested by
adults (age: F(5,54) > 48.0,
P < .001). The pre-
stimulus theta power was highest at Cz (elec-
trode: F(2,108) > 7.8,
P < .001).

Averaged filtered ERPs

Figure 3 illustrates that the maximal peak-to-
peak amplitude in the averaged (4-7 Hz) ERPs
did not depend on age (F(5,54) < 0.64,
P > .5).
In 6-8-year-old children, the maximal theta re-
sponse at Pz and Cz occurred later (age × time
window: F(5,54) > 3.37,
P < .05). It is also no-
ticeable that the frontal theta responses of chil-
dren were delayed relative to those of adults.
Maximal values were found at Cz (electrode:
F(2,108) > 6.1,
P < .001).

Single-sweep analyses

Figure 4 displays representative individual da-
ta to visualize the specific information reflect-
ed by each of the three parameters analyzed.
Results from statistical evaluation of single-
sweep amplitude, phase-locking, and enhance-
ment factor are summarized in Table 2.

- Maximal peak-to-peak amplitude

As presented in Table 2, the statistical out-
comes were similar for the three types of stim-
uli and will be discussed in terms of the overall
patterns for the passive, target, and nontarget
ERPs.

Figure 5a illustrates that: (1) adults had sig-
nificantly lower single-sweep amplitudes than
children from eaρh group, with F(l,54) >11.7
and
P < .005 for each of the univariate F-con-
trasts between single groups, (2) theta ampli-
tudes declined with age in children, and (3) the
developmental time courses differed between
the passive and task-related stimuli: For the
target and nontarget ERPs, no difference was
found among the groups of 6-9-year-olds, and
the 10-year-old children produced the lowest
amplitudes compared to the rest of the chil-



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