To explore whether the early automatic subcortical pathway was modulated by the negative emotional stimuli in the major depressive patients and healthy controls, as well as the aberrant functional connectivity of the subcortical pathway in the major depressive patients.

The technology of the magnetoencephalograph was used to record the brain response when 19 depressed patients and 17 healthy controls were under the negative emotion recognition task. The interested brain areas were the thalamus, the primary visual cortex, the fusiform gyrus, the inferior temporal cortex, the orbitofrontal cortex and the amygdala, and the interested time periods in this study were 0-100 ms, 0-150 ms, and 0-200 ms. The dynamic causal modeling was selected to compute the constructed model, and the Bayesian model was used to pick out the best model. Under the best model, the parameters of effective connectivity were analyzed with the method of permutation.

By Bayesian model selection, the subjects in healthy control responded to the negative emotion stimuli at as early as 0-100 ms, while the depressed patients responded at as early as 150-200 ms. During the period of 0-100 ms, the depressed patients presented reduced modulatory effect of the task on connection from left primary visual cortex to left orbitofrontal cortex (P=0.01), and reduced activity of intrinsic connectivity from right thalamus to right orbitofrontal cortex (P=0.04). During the period of 0-150 ms, the depressed patients increased activity of intrinsic connectivity from right primary visual cortex to right orbitofrontal cortex (P=0.01). During the period of 0-200 ms, the depressed patients reduced modulatory effect on connection from left thalamus to left orbitofrontal cortex (P=0.04), and reduced the activity of intrinsic connectivity from the right thalamus to right amygdala (P=0.04).

During the early period of the emotion processing stage, the depressed patients display delayed perception of negative emotion than the healthy people in a dynamic state. The subcortical pathway in the early stage is also aberrant in the depressed patients.

Depressive disorder; Negative bias; Magnetoencephalograph; Dynamic causal modeling