Hisaki Ozaki

Developmental characteristics of normal and mentally retarded children's EEGs.

Abstract It was necessary to reexamine the findings that the frequency of the EEG in children increases gradually with age. Using the method of spectrum analysis of EEG in normal and mentally retarded children, the authors examined the developmental characteristics of the frequency components both cross-sectionally and longitudinally. The EEG was taken monopolarly from 4 places along the midline (F, C, P, O) and the temporal places of the both hemispheres (LT, RT). Auto-power spectra of the EEG from the frontal, central and occipital regions were obtained by a minicomputer. Analysis time was 10 sec and frequency resolution was 1 3 c/sec . From 50 spectra an averaged auto-power spectrum was obtained. From the cross-sectional study, the following was obtained: 1. (1) In the normal group, the frequency of the dominant components changed with age until about 10 c/sec. However, the time course of the change was different among regions. The dominant component of about 10 c/sec appeared in all 3 regions at about 10 years. In the mentally retarded group, dominant components of about 10 c/sec were hardly observed and frequencies of the dominant and subordinate components varied widely among individuals and age groups. 2. (2) In both normal and mentally retarded groups, the alpha component appeared first in the occipital region as a subordinate component and subsequently became dominant. After the generation of the alpha component in the occipital region, it also appeared in the central and frontal regions, and became dominant in that order. 3. (3) In many cases in both normal and retarded groups, multiple peaks were observed when a dominant component in the spectrum appeared at frequency lower than 7 c/sec, subordinate ones were found at frequencies higher than 8 c/sec; conversely if a dominant component was generated at a frequency higher than 8 c/sec, subordinate ones were at lower frequencies. From the longitudinal study, the following results were obtained. 4. (4) In both normal and mentally retarded groups, earlier dominant components at the lower frequency later became the subordinate one without changing frequency or eventually disappeared. Moreover, a previously subordinate component or a new one at a higher frequency grew into a new dominant component. 5. (5) EEGs generated in the process of maturation are composed of different components at discrete frequencies that differ from each other in origin. The frequency of the dominant component is heightened not continuously but stepwise with increasing age. 6. (6) It may be accepted that the relative dominancy among the components reflects in part the maturational progress or retardation of the brain and that the processes of developmental change of the brain functioning in the retarded children are essentially identical to that of the normal, except for some pathological cases.

Topographic EEG changes due to hypobaric hypoxia at simulated high altitude

Multichannel human EEG signals were studied topographically in subjects exposed to an atmosphere of reduced air pressure in a chamber in which high-altitude conditions were simulated. EEG signals from 16 electrodes placed on the scalp were recorded simultaneously with electrocardiography and vertical eye movement. Baseline records were first obtained at sea level (PRE 0 m), and then at reduced air pressures corresponding to the altitudes of 3000 m, 4000 m, and 6000 m, respectively, and after returning to sea level (POST 0 m). A complete set of EEG records under all 6 conditions was obtained in 5 of the 15 subjects, and under 5 conditions (all except the 6000 m condition) in 3 other subjects. The spectral powers of 1 min epochs of the multichannel EEG signal under each altitude condition were compared to that at PRE 0 m using analysis of variance. Under the 3000 m condition, the spectral power of the 10-11 Hz components was significantly decreased and, with increasing altitude, significant decrease of spectral power was observed in a wider range of the alpha frequency band. Under the 6000 m condition, the decrease of spectral power of the alpha band in the posterior brain areas was -7 dB compared to the baseline. In contrast, the spectral power of the theta frequency band in anterior brain areas increased significantly in the 5000 m and 6000 m conditions. At the POST 0 m condition after return from the 5000 m condition (without exposure to the 6000 m condition), the EEG showed recovery to the level of the baseline PRE 0 m condition.(ABSTRACT TRUNCATED AT 250 WORDS)

On chronological changes in the basic EEG rhythm in persons with Down syndrome - with special reference to slowing of alpha waves.

The authors tried to know specificity of aging in persons with Down syndrome (DS) from the aspect of electroencephalograph (EEG) frequency changes through the cross-sectional and longitudinal studies, in comparison with normal persons as well as those with mentally retardation except the Down syndrome (non-DS MR). Subjects for a cross-sectional study were 265 persons with DS, 242 with non-DS MR and 239 healthy persons, and subjects for a follow-up study were 28 persons with DS and 14 with non-DS MR, whose EEGs were recorded repeatedly once a year during 8 or 9 years. Resting EEGs from the frontal, central and occipital regions were examined through power spectrum. In the cross-sectional study, the number of subjects with DS who showed dominant component within 8 Hz band of the basic rhythm reached maximum in its appearance rate at 40-44 years of age in the occipital area, but this slowing progressed already at 30-34 years of age. While in non-DS MR, the number of subjects who showed dominant component at 8 Hz reached maximum at 45-49 years of age, and this slowing of the basic rhythm was not so clear as in DS. In the follow-up study for subjects with DS, although the lowering in EEG frequency to 8 Hz took place in various years of age individually, earlier distinct decrease of the frequency was commonly noticed. These earlier steep lowering of EEG frequency was discussed in relation to the senile signs and to the decline of brain function referring to Alzheimer disease.

Topographic changes of ERP during a CPT-AX task at pre- and post-medication of methylphenidate in children with ADHD

Abstract To examine cerebral process of motor control in children with Attention-Deficit/Hyperactivity Disorder (ADHD; mean age, 11 years), event-related potentials (ERPs) during a cued continuous performance test (CPT-AX) were recorded from ADHD children an hour after psychostimulant (methylphenidate) dosage (Medicated ADHD), and without psychostimulants (Non-Medicated ADHD). These data were compared with ERPs in unmedicated age-matched normal controls (Non-ADHD). Hit rate in Non-medicated ADHD was significantly lower than that in Non-ADHD. However, their performance improved significantly due to psychostimulant medication, up to levels comparable to those of Non-ADHD subjects. In the ERP elicited by nontargets, P2 amplitudes in Non-Medicated ADHD were smaller than in Non-ADHD. Due to medication, P2 amplitudes increased and became comparable to that in Non-ADHD. Medication also improved a delayed onset of the P2 brain electric field in ADHD. Reduced amplitude of ERP in Non-Medicated ADHD suggests a lower activation at this relatively early stage of visual information processing in ADHD. In contrast, enhancement of ERP in Medicated ADHD implies that the medication contributes to allocate resources for orienting their attention to distinguish stimulus relevance, and to inhibit later processing of irrelevant stimuli properly. These results imply that methylphenidate improves response control in ADHD.

Linguistic lateralization in adolescents with Down syndrome revealed by a dichotic monitoring test

Linguistic lateralization in 10 adolescents with Down syndrome (average age: 15.7 years), 15 adolescents with intellectual disabilities of unknown etiology (average age: 17.8 years), 2 groups of children without disabilities (11 children, average age: 4.7 years; 10 children, average age: 8.5 years), and 14 adolescents without disabilities (average age: 18.7 years) was examined, using a dichotic monitoring test (DMT). Different Japanese words with 2 consonant-vowel syllables were presented to each ear simultaneously. Participants pressed a button when they heard the target word. The younger children without disabilities and the adolescents with intellectual disabilities exhibited a right-ear advantage, whereas the adolescents with Down syndrome showed the reverse pattern, i.e., a left-ear advantage. These results suggest that there is atypical linguistic lateralization in adolescents with Down syndrome.

The useful visual field and ERP topography in persons with intellectual disabilities

Abstract In order to elucidate physiological aspects underlying the narrower useful visual field in persons with intellectual disabilities, we examined ERP topography evoked by geometric figures presented within the perifovea. Three groups (persons with intellectual disabilities, normal children, and normal adults) have participated. A crosshatch for fixation was constantly presented at the center of CRT screen. Geometric figures were presented simultaneously for 300 ms at all four CRT corners. Four hexagons represented the non-target stimuli (85%), while one circle and three hexagons represented the target stimuli (15%). Eccentricity (distance between the crosshatch and stimulus shapes) was randomized (4°, 6°, 8°, 10° and 12°). EEGs were recorded under the following two conditions: (a) NON-TASK: subjects were asked to fixate the crosshatch. (b) DISCRIMINATE: subjects were asked to fixate and push a button if the stimulus contained a target. EEGs were averaged for non-targets. ERP differences between groups were more remarkable than those between conditions. ERP components at 100 ms (P1 with posterior positivity) and 160 ms (N1 with posterior negativity) after stimulation were observed in all groups. However, the latency of N1 in normal children and in persons with intellectual disabilities was longer than in normal adults. Furthermore, in normal children and adults, a P2 with posterior positivity appeared 200 ms after stimulation. No such P2 was observed in persons with intellectual disabilities. The P2 might reflect cerebral process responsible for particularly precise pattern analysis within the useful visual field for the visual cognition.

How regularities in stimulus series and in ISI affect on MMN in persons with intellectual disabilities

Abstract In this study, we investigated how regularities in time and in sequence affect on mismatched negativity (MMN) in persons with intellectual disabilities. Subjects were 10 normal adults (age: 22–26 years) and eight adults with intellectual disabilities (age: 28–46 years, IQ: 38–55). While the subjects engaged to watch a silent video program, stimulus tone was delivered through the speaker. Pip tone in 1000 Hz was used as a frequent stimulus with a probability of 0.8 and in 1050 Hz as a deviant stimulus with a probability of 0.2. Every combination of stimulus sequence (Regular vs. oddball) and Inter-Stimulus Intervals (ISI, fixed vs. random) were used as stimulus series. N1 component was observed in ERP in normal adult subjects. Then, P2 component followed in ERP by standard stimulus, but with reduced amplitude in ERP by deviant stimulus. These potential differences between ERP by standard and by deviant stimuli were observed in the map series with anterior dominant MMN. Compared to MMN in regular series, a larger amplitude of MMN in oddball series was remarkable. The N1 component was also observed in the ERP in persons with intellectual disabilities. However, map series of subtracted ERP in persons with intellectual disabilities indicate poorer MMN in oddball series with fixed ISI and no MMN in the remaining three conditions. Therefore, longer sequence of standard stimuli with fixed timing will be needed to establish a memory trace in automatic auditory information processing in persons with intellectual disabilities.

Topographic ERP changes due to displacements of visuo-spatial attention

Abstract In order to explore the cerebral processes of visuo-spatial attention shifts, the spatio-temporal characteristics of ERPs to targets following a spatial cue were examined topographically. Subjects were asked to respond selectively to a target presented 200 ms after offset of a spatial cue. Valid targets (75%) appeared at cue position; invalid targets (25%) were presented at a different position than the cue. In valid trials, an anterior negative deflection of Nd and a single-peaked P3 were observed with shorter reaction time. In invalid trials, a posterior N2–P3 complex was observed with delayed reaction time. Spatio-temporal patterns of brain electric fields (BEF) to valid and invalid trials differed between 240 and 280 ms after target presentation. Regardless of target locations, the BEF in valid trials was characterized by anterior negative/posterior positive distribution. On invalid trials, where subjects were forced to shift their visuo-spatial attention from the cue to the target, the BEF was characterized by an anterior positive/posterior negative distribution for all cue-target pairs except those presented in the upper visual field. Therefore, the BEF within 240–280 ms after the target presentation might be concerned with cerebral processes of visuo-spatial attention shift, i.e., with recapturing/evaluating target.

Topographic change of ERP due to discrimination of CV syllables with various vowel durations

Abstract This study aims to investigate the cerebral process of discrimination of consonant–vowel (CV) syllables differing in vowel length. The subjects were normal adults. A single human CV syllable (/ma/) and five variants with reduced vowel duration were used as stimuli. EEGs were recorded from 16 scalp locations under the following two conditions: (1) ignore condition: subjects heard stimulus sounds while relaxing and (2) discriminate condition: subjects were asked to discriminate unreduced CV syllable (/ma/) as a target and press the button when they detected it. Regardless of the vowel lengths of the CV syllable, P2 and P3 components were observed in both conditions. With the reduction of the vowel duration, the scalp distributions of P2 shifted from anterior to vertex in the ignore condition and from posterior to vertex in the discriminate condition. Therefore, not only vowel duration but also the task condition affected the generators of the P2 component. Vowel duration also affected the generator of the P3 component. In the ignore condition, the unreduced CV syllable evoked an anterior positive, and CV syllables with reduced vowels evoked posterior positive P3s. However, in the discriminate condition, the P3 component was anterior-negative/posterior-positive distributed as long as the CV syllable was perceived as /ma/. Therefore, the brain electrical fields of the P3 component might reflect cortical discrimination in the categorical hearing of human CV syllables.

P129: ERP study on cerebral integration of audio-visual information in male and female

a higher sensitivity (31.7%) vs OCT (19.9%; p=0.005); VEP/OCT combined detected abnormalities in 39.2%. In this subgroup, VEP score and global RNFL thickness were significantly correlated with EDSS (RNFL: Spearman ρ= −0.22, p<0.04; VEP score: ρ=0.30, p<0.0001), disease duration (RNFL r=-0.35, p=0.001; VEP score: ρ=0.25, p=0.001), not with VA. Conclusions: The present findings confirm a higher sensitivity of VEPs in the subacute phases of optic neuritis (less than 3 months) and in asymptomatic eyes. This discrepancy fades off after more than 3 months from the ON episode, allowing for retrograde degeneration to occur and thus increasing OCT sensitivity. However, even at this stage the combination of the two exams allows to increase our overall sensitivity in detecting optic nerve damage. Finally, the correlation with disability and DD favours the usefulness of both techniques in monitoring MS patients, to be verified through longitudinal studies.