title: Global synchronization index as a biological correlate of cognitive decline in Alzheimer's disease.
abstract: OBJECTIVE
  The recently developed global synchronization index (GSI) quantifies synchronization between neuronal signals at multiple sites. This study explored the clinical significance of the GSI in Alzheimer's disease (AD) patients.
  
  
  METHODS
  Electroencephalograms were recorded from 25 AD patients and 22 age-matched healthy normal controls (NC). GSI values were computed both across the entire frequency band and separately in the delta, theta, alpha, beta1, beta2, beta3, and gamma bands. The Mini-Mental Status Examination (MMSE) and Clinical Dementia Rating scale (CDR) were used to assess the symptom severity.
  
  
  RESULTS
  GSI values in the beta1, beta2, beta3, and gamma bands were significantly lower in AD patients than in NC. GSI values in the beta and gamma bands were positively correlated with the MMSE scores in all participants (AD and NC). In AD patients, GSI values were negatively correlated with MMSE scores in the delta bands, but positively correlated in the beta1 and gamma band. Also, GSI values were positively correlated with CDR scores in the delta bands, but negatively correlated in the gamma band.
  
  
  CONCLUSIONS
  GSI values of mainly high-frequency bands were significantly lower in AD patients than in NC, they were significantly correlated with scores on symptom severity scales.
  
  
  CONCLUSIONS
  Our results suggest that GSI values are a useful biological correlate of cognitive decline in AD patients.
authors.affiliation: Department of Neuropsychiatry, Inje University Ilsan Paik Hospital, Goyang, South Korea; Clinical Emotion and Cognition Research Laboratory, Goyang, South Korea.
authors.forename: Seung-Hwan
authors.initials: SH
authors.lastname: Lee
authors.forename: Young-Min
authors.initials: YM
authors.lastname: Park
authors.forename: Do-Won
authors.initials: DW
authors.lastname: Kim
authors.forename: Chang-Hwan
authors.initials: CH
authors.lastname: Im
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000503:physiopathology* / Q000523:psychology; D003072:Cognition Disorders / Q000503:physiopathology*; D003344:Cortical Synchronization; D005260:Female; D006801:Humans; D008297:Male; D012720:Severity of Illness Index