Negative slow potential change (contingent negative variation or CNV) in human cortex which develops in the foreperiod of a reaction-time experiment was studied as a function of motivational variables. When the warning signal indicated that a difficult-to-detect auditory stimulus would follow, CNV was greater than when an easily detected stimulus was signaled. Instructing Ss to press a key at the onset of the second stimulus resulted in development of larger anticipatory CNV than when no response was instructed. When muscular effort required to complete a response to the 2nd stimulus was varied, larger CNV accompanied greater effort. These findings extend those of other investigators and support the conclusion that CNV reflects cerebral mechanisms related to motivation.

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BackgroundElectroencephalography (EEG) characteristics associated with treatment response show potential for informing treatment choices for major depressive disorder, but to date, no robust markers have been identified. Variable findings might be due to the use of group analyses on a relatively heterogeneous population, which neglect individual variation. However, the correspondence between group level findings and individual brain characteristics has not been extensively investigated. Using single-subject analyses, we explored the extent to which group-based EEG connectivity and complexity characteristics associated with treatment response could be identified in individual patients.MethodsResting-state EEG data and Montgomery-Åsberg Depression Rating Scale symptom scores were collected from 43 patients with depression (23 females) before, at 1 and 12 weeks of treatment with escitalopram, bupropion or both. The multivariate statistical technique partial least squares was used to: 1) identify differences in EEG connectivity (weighted phase lag index) and complexity (multiscale entropy) between responders and non-responders to treatment (≥50% and <50% reduction in symptoms, respectively, by week 12), and 2) determine whether group patterns could be identified in individual patients.ResultsThe group analyses distinguished groups. Responders showed decreased alpha and increased beta connectivity and early, widespread decreases in coarse scale entropy over treatment. Non-responders showed an opposite connectivity pattern, and later, spatially confined decreases in coarse scale entropy. These EEG characteristics were identified in ∼40-60% of individual patients.ConclusionSubstantial individual variation highlighted by the single-subject analyses might explain why robust EEG markers of antidepressant treatment response have not been identified. As up to 60% of patients in our sample was not well represented by the group results, individual variation needs to be considered when investigating clinically useful characteristics of antidepressant treatment response.

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