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Between-Subject versus Within-Subject EEG Similarity

Do Brain Waves Have Individuality?

From the very beginning of EEG recordings authors have described the distinct individuality of human brain wave patterns. Among the first authors who investigated the phenomenon in a quantitative and systematic way were Travis and Gottlober who published as early as 1936 and 1937 two articles entitled "Do brain-waves have individuality?" and "How consistent are and individual's brain potentials from day to day?". At the same time (1936) Davis and Davis published the first twin study, stating that the within-pair differences of the resting EEG derived from monozygotic twins were not greater than the fluctuations within a subject over time.

Computerized Recognition of Persons

To address these questions we performed a normative study with 138 healthy volunteers (75 males and 63 females with ages between 20 and 35 years) who had been selected by means of a specifically developed "health" questionnaire comprising 65 somatic, psychiatric and social items. The EEGs of these persons were recorded twice at an interval of 14 days and at a fixed time between 8 and 10 o'clock in the morning, thus excluding variations due to circadiane rhythms. All EEGs were recorded under comparable experimental conditions (bipolar leads: P3-O1, P4-O2, T3-T5, T4-T6, T5-O1, T6-O2). Using these data we performed systematic inter-individual comparisons (all possible pairings) and compared the resulting distribution of EEG similarities with the distribution of within-subject EEG similarities derived from comparisons between the recordings at 14-day intervals (Figure). The data enabled a computerized identification of persons at a sensitivity and specificity of >90%.

Long-Term Stability (5-Year Intervals)

To address the question of longterm stability of individual EEG characteristics we have carried out a 5-year follow-up of 30 subjects (15 males, 15 females, ages 25-40 years) using the same experimental design as before. The indeed remarkable stability of individual EEG characteristics over time (cf. 4 subjects shown on web page "long-term stability") enabled a computerized identification of persons at a similar rate as for 14-day intervals: 26 subjects (86.7% with a perfect one-to-one mapping between first recording and second recording 5 years later, 2 individuals (6.7%) whose patterns corresponded to the correct one plus at least one additional pattern, and 5 individuals (6.7%) whose patterns did not correctly correspond, though well above the average between-subject value.

References

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Stassen HH, Lykken DT, Bomben G: The within-pair similarity of twins reared apart. Eur Arch Psychiatr Neurol Sci 1988; 237: 244-252
Stassen HH, Lykken DT, Propping P, Bomben G: Genetic determination of the human EEG (survey of recent results from twins reared together and apart). Human Genetics 1988; 80: 165-176
Stassen HH, Lykken DT, Propping P: Zwillingsuntersuchungen zur Genetik des normalen Elektroenzephalogramms. In: P. Baumann (ed): Biologische Psychiatrie der Gegenwart, Wien: Springer 1993, 139-144
Kaprio J, Buchsbaum M, Gottesman II, Heath A, Körner J, Kringlen E, McGuffin P, Propping P, Rietschel M, Stassen HH: What can twin studies contribute to the understanding of adult psychopathology? In: T.J. Bouchard jr. and P. Propping: Twins as a tool for behavioral genetics. Chichester: John Wiley & Sons, Dahlem Workshop Reports, Life Sciences Research Report 1993; 53: 287-299
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Dünki RM, Schmid GB, Stassen HH: Intraindividual specificity and stability of the human EEG: Linear vs. nonlinear approaches. Meth Inform Med 2000; 39: 78-82
Umbricht D, Koller R, Schmid L, Skrabo A, Grübel C, Huber T, Stassen HH: How specific are deficits in mismatch negativity generation to schizophrenia? Biol Psychiatry 2003; 53: 1120-1131
Stassen HH: EEG and evoked potentials. In: D. Cooper (ed) Nature Encyclopedia of the Human Genome. Nature Publishing Group, London 2003; 3: 266-269
Weisbrod M, Hill H, Sauer H, Niethammer R, Guggenbühl S, Stassen HH: Nongenetic pathologic developments of brain-wave patterns in monozygotic twins discordant and concordant for schizophrenia. Am J Med Genetics B 2004; 125: 1-9
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frequency distribution
Fig. 6: Discrimination between the distributions of inter-individual (lower half) and intra-individual (upper half) similarity coefficients based on 81 healthy volunteers (47 males, 34 females) and measurements at 14 day intervals under the condition of quiet wakefulness (eyes closed; 4 channels: T3-T5, T5-O1, T4-T6, T6-O2).

The computerized re-classification yielded 70 individuals (86.4%) with a perfect one-to-one mapping between first recording and second recording 14 days later, 6 individuals (7.4%) whose patterns corresponded to the correct one plus at least one additional pattern, and 5 individuals (6.2%) whose patterns did not correctly correspond (for unknown reasons).
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