Novel Stimulation Approaches with ECT: Why Everything Old May be New Again

Effective connectivity between deep brain stimulation targets in individuals with treatment-resistant depression

The therapeutic effect of deep brain stimulation on patients with treatment-resistant depression is strongly dependent on the connectivity of the stimulation region with other regions associated with depression. The aims of this study are to characterize the effective connectivity between the brain regions playing important roles in depression and further investigate the underlying pathophysiological mechanisms of treatment-resistant depression and the mechanisms involving deep brain stimulation. Thirty-three individuals with treatment-resistant depression and 29 healthy control subjects were examined. All subjects underwent resting-state functional MRI scanning. The coupling parameters reflecting the causal interactions among deep brain stimulation targets and medial prefrontal cortex were estimated using spectral dynamic causal modelling. Our results showed that compared to the healthy control subjects, in the left hemisphere of treatment-resistant depression patients, the nucleus accumbens was inhibited by the inferior thalamic peduncle and excited the ventral caudate and the subcallosal cingulate gyrus, which in turn excited the lateral habenula. In the right hemisphere, the lateral habenula inhibited the ventral caudate and the nucleus accumbens, both of which inhibited the inferior thalamic peduncle, which in turn inhibited the cingulate gyrus. The ventral caudate excited the lateral habenula and the cingulate gyrus, which excited the medial prefrontal cortex. Furthermore, these effective connectivity links varied between males and females, and the left and right hemispheres. Our findings suggest that intrinsic excitatory/inhibitory connections between deep brain stimulation targets are impaired in treatment-resistant depression patients, and that these connections are sex dependent and hemispherically lateralized. This knowledge can help to better understand the underlying mechanisms of treatment-resistant depression, and along with tractography, structural imaging, and other relevant clinical information, may assist to determine the appropriate region for deep brain stimulation therapy in each treatment-resistant depression patient.

Characterization of brain functional connectivity in treatment-resistant depression

OBJECTIVE

To characterize the functional connectivity (FC) of target brain regions for deep brain stimulation (DBS) in patients with treatment-resistant depression (TRD), and to evaluate its gender and brain lateralization dependence.

METHODS

Thirty-one TRD patients and twenty-nine healthy control (HC) subjects participated. FC of subcallosal cingulate gyrus (SCG), ventral caudate (VCa), nucleus accumbens (NAc), lateral habenula (LHb), and inferior thalamic peduncle (ITP) were evaluated using resting-state fMRI. FC was characterized by calculating the nodal 'degree', a major feature of the graph theory.

RESULTS

The degree measures of the left and right VCa, the left LHb, and the left ITP were significantly greater in the TRD than in the HC group. The degree was greater in females with TRD in all these regions except the right LHb. Finally, the left hemisphere was generally more affected by depression and presented significant degrees in LHb and ITP regions of the patients.

CONCLUSION

Our findings demonstrate the ability of degree to characterize brain FC and identify the regions with abnormal activities in TRD patients. This implies that the degree may have the potential to be used as an important graph-theoretical feature to further investigate the mechanisms underlying TRD, and consequently along with other diagnostic markers, to assist in the determination of the appropriate target region for DBS treatment in TRD patients.