The development of sleep spindles was studied quantitatively in 32 healthy subjects between the ages of 4 and 24 years. The peak frequency distribution of the spindles showed a bimodal pattern with 11.0 to 12.75 Hz in the frontal area and 12.5 to 14.5 Hz in the centroparietal area. The two types of spindle activity showed different courses of maturation. The peak frequency of the centroparietal spindles gradually increased linearly with age, whereas the frontal spindles abruptly increased in frequency during early adolescence. Regarding the power spectra, while centroparietal spindles showed little change in power from 4 to 24 years of age, frontal spindles decreased remarkably in power and became stable at about 13 years of age. The two types of spindles and the difference in their development may suggest the existence of different generators or a topographical difference during maturation in the thalamocortical network. The frontal spindle activity could be a good indicator to evaluate CNS maturation in young children and adolescents.
The present study examined the clinical significance of anterior bradyrhythmia (AB), which was described by Gibbs and Gibbs in 1964. The significance of AB in this report was indefinite because of unclear criteria and underdeveloped neuroradiology. We proposed a set of criteria of AB and reevaluated the clinical significance of the EEG pattern in correlation with the clinical and the computerized topography (CT) findings of the patients. The study material was 4019 EEGs examined in our laboratory during a 1-year period (1991). AB was recorded in 20 patients (0.5%), whose mean age was 69.8 years. Its incidence tended to increase with age. Sixteen patients [table: see text] (80%) had dementia and were classified into two types according to clinical features, as Binswanger (B)-type and Alzheimer (A)-type. B-type patients had gait disturbance, urinary incontinence, hemiparesis, and ECG abnormalities, and showed leuko-araiosis on CT. A-type patients had only dementia, and showed frontoparietal atrophy on CT. Delirium was found in 7 (35%) out of the 20 patients with AB, which may be an additional factor related to the appearance of the EEG pattern. B-type had lower frequency of AB than A-type. Both types showed slowed background activities; the alpha rhythm of B-type had lower frequency and tended to have higher amplitude than that of A-type. These EEG abnormalities may be indicative of subcortical or cortical dysfunction in the frontal areas.
The theta rhythm that appears in the frontal midline was studied morphologically and clinically in EEGs performed on 788 patients and 161 normal subjects in their late teens or older. This theta rhythm was classified into 2 types. The Type 1 theta rhythm appeared in short bursts maximally in the Fz lead and spread mainly to the anterior region. It had a high frequency, low voltage and regular waveform. The Type 2 theta rhythm appeared in long runs maximally in the Fz lead and spread mainly to the posterior areas. It had a relatively low frequency, high voltage and irregular waveform. Type 1 was observed in a younger age group (mean age: 20.3 years) that was comprised of healthy subjects and one mentally retarded patient. In no case was the Type 1 theta rhythm accompanied by a paroxysmal EEG abnormality. We therefore believe that Type 1 is a physiological EEG activity (Fm theta). On the other hand, Type 2 was observed in a relatively older age group (mean age: 30.7 years) comprised of patients diagnosed as having epilepsy or intractable headaches. Five of 9 cases showed epileptic EEG abnormalities. We therefore believe that Type 2 might have clinical significance in diagnosis of epilepsy and other cerebral dysfunctions. The EEG pattern that we call the frontal mid-line theta rhythm may be either a physiological theta rhythm or an abnormal discharge. It is possible to determine whether the theta rhythm is the former or the latter, and we believe this differentiation to be clinically important.
We studied clinical aspects of the "third rhythm," which was first described by Niedermeyer as alpha-like activity of the temporal lobe. By scalp EEG, temporal alpha-like activity was recorded in 15 (0.30%) of 4929 patients over 20 years of age. The temporal alpha-like activity was observed in 5 patients who had clinical and brain imaging findings indicating the presence of a cerebrovascular disorder. The alpha-like rhythm of these patients was left-sided, and wicket spikes appeared in the same region as the alpha-like rhythms in 4 of the 5 patients. In 8 of the 15, the temporal alpha-like rhythm was recorded over the defective bone or replacement bone after intracranial surgery. The alpha-like rhythm of these patients was similar to breach rhythm in the temporal region. The remaining 2 patients had not undergone intracranial surgery nor did they show symptoms of cerebrovascular disorders. The temporal alpha-like rhythms in one of these 2 might be a physiological third rhythm detected by scalp EEG through congenital bone thinning. Our observation supports the existence of intrinsic activity of the temporal lobe (the third rhythm). The third rhythm can be recorded by routine scalp EEG in some clinical conditions, and it is important to recognize this rhythm when one encounters temporal rhythmic activity independent of alpha rhythm of the occipital lobe.
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