Amygdalar interhemispheric functional connectivity differs between the non-depressed and depressed human brain

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Psychiatry

Background:

• The amygdalae are crucial for emotion, attention, and memory, with dysfunction linked to depression.
• Cortical hemispheric specialization models are supported by lesion and neuroimaging studies, but amygdalar specialization findings are inconsistent.
• Primate amygdalae largely lack direct interhemispheric connections via the anterior commissure (AC), contrasting with rodents.

Purpose of the Study:

• To investigate human amygdalar interhemispheric connectivity.
• To explore the influence of frontocortical hemispheric specialization on amygdalar connectivity.
• To compare amygdalar connectivity in depressed versus non-depressed individuals.

Main Methods:

• Functional magnetic resonance imaging (fMRI).
• Positron emission tomography (PET).
• Analysis of amygdalar interhemispheric functional connectivity.

Main Results:

• Modest evidence of amygdalar interhemispheric functional connectivity in non-depressed individuals.
• Strong evidence of amygdalar interhemispheric functional connectivity in depressed individuals.
• Findings suggest a difference in connectivity related to depression status.

Conclusions:

• The lack of direct interhemispheric amygdalar connections in primates may stem from frontocortical specialization.
• Increased amygdalar interhemispheric functional connectivity in depression indicates dysfunctional frontocortical-amygdalar interactions.
• This connectivity pattern may be a key feature of clinical depression's neurobiology.