Frontal Theta Asymmetry as a Biomarker of Depression.

INTRODUCTION: Electroencephalography (EEG) has been used extensively to study affective disorders. Quantitative spectral analysis of an EEG scan has been used to assess the biological basis of emotional disorders such as depression as well as to investigate biomarkers of affective disorders. Inter-hemispheric asymmetries in both baseline and stimulus-evoked frequencies (alpha, beta, theta, and delta) are potential biomarkers of depression. The role of frontal alpha asymmetry has been established, but other spectral frequencies such as frontal theta remain elusive. We compared the hemispheric differences in frontal theta power in depressed patients and controls before and during listening to music to study the correlation of frontal theta asymmetry with depression. METHODS: To determine whether stimulus-evoked frontal theta asymmetry is a biomarker of depression, we compared 23 patients with mild depression (based on the Hamilton Depression Rating Scale) with 17 age- and sex-matched controls by conducting EEG at rest and after listening to Indian classical music. RESULTS: In controls without depression, the mean frontal theta power of the left hemisphere and frontal theta asymmetry increased significantly during music listening. In depressed patients, frontal theta asymmetry was reversed during music listening. CONCLUSION: Frontal theta asymmetry is a potential biomarker of depression.

Rapid impact of effective treatment on transmission of multidrug-resistant tuberculosis.

BACKGROUND: Effective treatment for drug-susceptible tuberculosis (TB) rapidly renders patients non-infectious, long before conversion of sputum acid-fast smear or culture to negative. Multidrug-resistant TB (MDR-TB) patients on treatment are currently assumed to remain infectious for months. While the resources required for prolonged hospitalization are a barrier to the scale-up of MDR-TB treatment, the safety of community treatment is clear. OBJECTIVES: To estimate the impact of treatment on infectiousness among MDR-TB patients. METHODS: A series of five human-to-guinea pig TB transmission studies was conducted to test various interventions for infection control. Guinea pigs in adjacent chambers were exposed to exhaust air from a hospital ward occupied by mostly sputum smear- and culture-positive MDR-TB patients. The guinea pigs then underwent tuberculin skin testing for infection. Only the control groups of guinea pigs from each study (no interventions used) provide the data for this analysis. The number of guinea pigs infected in each study is reported and correlated with Mycobacterium tuberculosis drug susceptibility relative to treatment. RESULTS: Despite exposure to presumably infectious MDR-TB patients, infection percentages among guinea pigs ranged from 1% to 77% in the five experiments conducted. In one experiment in which guinea pigs were exposed to 27 MDR-TB patients newly started on effective treatment for 3 months, there was minimal transmission. In four other experiments with greater transmission, guinea pigs had been exposed to patients with unsuspected extensively drug-resistant tuberculosis who were not on effective treatment. CONCLUSIONS: In this model, effective treatment appears to render MDR-TB patients rapidly non-infectious. Further prospective studies on this subject are needed.