Impaired interhemispheric interactions in patients with major depression

Area of Science:

• Neuroscience
• Psychiatry
• Neuromodulation

Background:

• Major depressive disorder is associated with interhemispheric imbalances in prefrontal and motor cortex.
• Understanding these imbalances is crucial for developing effective treatments.

Purpose of the Study:

• To investigate interhemispheric interactions in major depression using repetitive transcranial magnetic stimulation (rTMS).
• To compare the effects of rTMS on corticospinal excitability between depressed patients and healthy controls.

Main Methods:

• Thirteen patients with major depression and 14 healthy subjects underwent 1 Hz rTMS applied to the left primary motor cortex.
• Corticospinal excitability was assessed in both the stimulated (left) and contralateral (right) motor cortices before and after rTMS.
• Interhemispheric effects were compared between groups.

Main Results:

• Healthy subjects showed decreased excitability in the left motor cortex and increased excitability in the right motor cortex post-rTMS.
• Depressed subjects showed decreased excitability in the left motor cortex but no significant change in the right motor cortex.
• A correlation was found between reduced interhemispheric modulation and depression severity (Beck Depression Inventory scores).

Conclusions:

• Patients with major depression exhibit decreased interhemispheric modulation compared to healthy individuals.
• Findings support the hypothesis that mood disorders involve slower interhemispheric switching mechanisms.
• rTMS can reveal distinct patterns of brain network dysfunction in major depression.