title: Heredity of cognitive functions and personality in twins.
abstract: OBJECTIVE
  The inheritance of cognitive functions and personality is still a problem under investigation. A classical method, investigation of twins, is often used to find relative contributions from genetics and the environment to quantitative traits. The aim of this study was to investigate a possible influence of heredity on cognitive functions (by applying the Raven test) and personality traits (according to the Eysenck's theory) in twins.
  
  
  METHODS
  In total, 139 pairs of same-sex twins were investigated. The zygosity of the twin pairs was confirmed through genotyping with 15 molecular DNA markers. Constructive thinking was assessed using the Raven test. Personality assessment was conducted using the Eysenck Personality Questionnaire (EPQ) in Lithuanian.
  
  
  RESULTS
  The difference in the total number of incorrect solutions between monozygotic (MZ) and dizygotic (DZ) twin pairs younger than 15 years was not significant; however, in the group older than 15 years, this difference was found to be significant. Based on the total number of incorrect solutions, the concordance in the MZ twins was greater than in the DZ twins. The same tendency was found with cumulative EPQ scores on the extraversion scale.
  
  
  CONCLUSIONS
  The results imply that the quality of cognitive functions and personality traits (extraversion) can be influenced by heredity. This confirms previous findings on the heritability of cognitive factors and personality traits.
authors.affiliation: Institute of Biological Systems and Genetics, Medical Academy, Lithuanian University of Health Sciences, Tilžės 18, 47181 Kaunas, Lithuania. lkalasuniene@yahoo.com.
authors.forename: Loreta
authors.initials: L
authors.lastname: Kalasūnienė
authors.forename: Antanas
authors.initials: A
authors.lastname: Goštautas
authors.forename: Algimantas
authors.initials: A
authors.lastname: Sinkus
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D003071:Cognition; D005120:Extraversion, Psychological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010551:Personality / Q000235:genetics*; D013694:Temperament; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*; D055815:Young Adult