Source localization of posterior slow waves of youth using dipole modeling.

AIM: Posterior slow waves of youth have a well-known electroencephalographic pattern that peaks in adolescence and usually disappears in adulthood. In general, posterior slow waves of youth are regarded as normal, but some reports have suggested that their presence is related to immature personalities or inappropriate social behavior. The physiological significance of this electroencephalographic pattern, however, remains unclear. The purpose of this study was to investigate the neural origins of posterior slow waves of youth using dipole source modeling. METHODS: Electroencephalographic epochs, including clear posterior slow waves of youth, were visually selected from electroencephalograms obtained from six normal adolescents using 25 scalp electrodes. The selected epochs were then averaged by arranging the negative peak of the slow waves at the occipital area of each epoch on the time axis. The averaged waveforms consisting of six right and one left posterior slow waves of youth were used for dipole source analysis. A single equivalent current dipole was estimated for the averaged waveforms. RESULTS: The best equivalent current dipoles were estimated to be located in or around the fusiform and middle occipital gyrus ipsilateral to the posterior slow waves of youth. CONCLUSIONS: The location of the estimated dipoles of posterior slow waves of youth was on the so-called ventral visual pathway. Further research is required to clarify the physiological significance of posterior slow waves of youth with respect to their origin.

Dipole source analysis of temporal slow waves in the elderly.

BACKGROUND: Temporal low-voltage irregular delta-waves (TLID) are often found in elderly subjects. The physiological significance of TLID has not been clarified; however, our previous studies suggest that TLID are associated with mild cerebrovascular dysfunction. OBJECTIVE: The present study aimed to reveal the origin of TLID and their neural mechanisms by dipole source modeling. METHODS: From electroencephalography records taken from 21 scalp electrodes, clear and typical TLID of 6 elderly subjects (mean age, 69 +/- 6.2 years) were selected. Among these, we selected and averaged 7-12 clear TLID on the left side in each subject, and estimated a single equivalent current dipole for the averaged TLID. RESULTS: The best equivalent current dipoles were estimated to be located in the medial part of the temporal lobe in or near the parahippocampal gyrus in the hemisphere ipsilateral to the TLID, with a high reliability in all subjects. CONCLUSIONS: Considering the source localization of TLID, TLID seem to indicate certain dysfunctions of the hippocampus or adjacent regions. This is the first study to report the cerebral origin of TLID and suggest its physiological significance.

Late-onset depression: can EEG abnormalities help in clinical sub-typing?

BACKGROUND: The purpose of this study was to determine the frequency of EEG abnormalities indicative of mild cerebrovascular dysfunction in patients with late-onset depression and to correlate these abnormalities with clinical features. METHODS: The subjects, aged > or = 50 years, were 51 outpatients with major depression diagnosed according to DSM-IV criteria. They were living in the community and prospectively selected at their initial consultation for mostly mild-moderate depression. We also included 32 normal age-matched controls. We examined basic rhythms and temporal slow waves on EEG and determined the Hamilton Rating Scale for Depression (HAMD) as a scale for the severity of psychiatric symptoms. RESULTS: Temporal slow waves were more common in depressed patients (47%) than in normal controls (22%). Depressed patients with temporal slow waves had significantly lower frequency of family history of mood disorders (P<0.05). There was no difference in the total score of HAMD between patients with and without temporal slow waves, however, each score of HAMD in patients with temporal slow waves showed a significantly lower score for "feeling of guilt" (P<0.01) and a significantly higher score for "general somatic symptoms" (P<0.01) and "hypochondriasis" (P<0.01). CONCLUSIONS: Our EEG study suggested that temporal slow waves, which were probably associated with subtle cerebrovascular lesions, might reflect vulnerability to late-onset depression. In addition, depressed patients with temporal slow waves could be classified as a subgroup of heterogeneous late-onset depression based on the clinical findings. These results must be interpreted within the limitations of the sample selection procedure.