title: EEG power asymmetry and functional connectivity as a marker of treatment effectiveness in DBS surgery for depression.
abstract: Recently, deep brain stimulation (DBS) has been evaluated as an experimental therapy for treatment-resistant depression. Although there have been encouraging results in open-label trials, about half of the patients fail to achieve meaningful benefit. Although progress has been made in understanding the neurobiology of MDD, the ability to characterize differences in brain dynamics between those who do and do not benefit from DBS is lacking. In this study, we investigated EEG resting-state data recorded from 12 patients that have undergone DBS surgery. Of those, six patients were classified as responders to DBS, defined as an improvement of 50% or more on the 17-item Hamilton Rating Scale for Depression (HAMD-17). We compared hemispheric frontal theta and parietal alpha power asymmetry and synchronization asymmetry between responders and non-responders. Hemispheric power asymmetry showed statistically significant differences between responders and non-responders with healthy controls showing an asymmetry similar to responders but opposite to non-responders. This asymmetry was characterized by an increase in frontal theta in the right hemisphere relative to the left combined with an increase in parietal alpha in the left hemisphere relative to the right in non-responders compared with responders. Hemispheric mean synchronization asymmetry showed a statistically significant difference between responders and non-responders in the theta band, with healthy controls showing an asymmetry similar to responders but opposite to non-responders. This asymmetry resulted from an increase in frontal synchronization in the right hemisphere relative to the left combined with an increase in parietal synchronization in the left hemisphere relative to the right in non-responders compared with responders. Connectivity diagrams revealed long-range differences in frontal/central-parietal connectivity between the two groups in the theta band. This pattern was observed irrespective of whether EEG data were collected with active DBS or with the DBS stimulation turned off, suggesting stable functional and possibly structural modifications that may be attributed to plasticity.
authors.affiliation: 1] Krembil Neuroscience Center, University Health Network, Toronto, ON, Canada [2] Toronto Western Research Institute, University Health Network, Toronto, ON, Canada.
authors.forename: Maher A
authors.initials: MA
authors.lastname: Quraan
authors.affiliation: 1] Department of Psychology, University of Calgary, Calgary, AB, Canada [2] Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada.
authors.forename: Andrea B
authors.initials: AB
authors.lastname: Protzner
authors.affiliation: 1] Department of Psychiatry, University of Toronto, Toronto, ON, Canada [2] Institute of Medical Sciences, University of Toronto, Toronto, ON, Canada [3] Centre for Addiction and Mental Health, Toronto, ON, Canada.
authors.forename: Zafiris J
authors.initials: ZJ
authors.lastname: Daskalakis
authors.affiliation: 1] Department of Psychiatry, University of Toronto, Toronto, ON, Canada [2] Department of Psychiatry, University Health Network, Toronto, ON, Canada.
authors.forename: Peter
authors.initials: P
authors.lastname: Giacobbe
authors.affiliation: Department of Psychiatry, University Health Network, Toronto, ON, Canada.
authors.forename: Chris W
authors.initials: CW
authors.lastname: Tang
authors.affiliation: 1] Department of Psychiatry, University of Toronto, Toronto, ON, Canada [2] Institute of Medical Sciences, University of Toronto, Toronto, ON, Canada [3] Department of Psychiatry, University Health Network, Toronto, ON, Canada.
authors.forename: Sidney H
authors.initials: SH
authors.lastname: Kennedy
authors.affiliation: 1] Krembil Neuroscience Center, University Health Network, Toronto, ON, Canada [2] Toronto Western Research Institute, University Health Network, Toronto, ON, Canada [3] Department of Surgery, University of Toronto, Toronto, ON, Canada.
authors.forename: Andres M
authors.initials: AM
authors.lastname: Lozano
authors.affiliation: 1] Krembil Neuroscience Center, University Health Network, Toronto, ON, Canada [2] Toronto Western Research Institute, University Health Network, Toronto, ON, Canada [3] Institute of Medical Sciences, University of Toronto, Toronto, ON, Canada [4] Department of Psychology, University of Toronto, Toronto, ON, Canada.
authors.forename: Mary P
authors.initials: MP
authors.lastname: McAndrews
mesh_terms: D000328:Adult; D000513:Alpha Rhythm; D001921:Brain / Q000503:physiopathology*; D046690:Deep Brain Stimulation; D003865:Major Depressive Disorder / Q000175:diagnosis / Q000503:physiopathology* / Q000628:therapy*; D004569:Electroencephalography; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D008875:Middle Aged; D011569:Psychiatric Status Rating Scales; D012146:Rest / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D013826:Theta Rhythm; D016896:Treatment Outcome; D055815:Young Adult