An Evolutionarily Conserved Depression Mechanism: Are There Implications for Psychotherapy?

Increasingly sophisticated research, accessing state-of-the-art neurochemical, neuroendocrine, pharmacologic, molecular genetic, and neuroimaging methods has generated a densely populated landscape of biological correlates of depression. Douglas Watt and Jaak Panksepp masterfully survey this rich and complex landscape and observe that what is sorely lacking in our understanding of depression is a model that integrates the disparate biological findings and links them to the core psychological and behavioral features of depression. They propose that such a model of depression may be derived from an examination of the separation-distress behavioral system, common to so many animal species. A separation-distress motivational system that, in the event the young animal is separated from its caregiver, prompts the animal to send out a distress signal and to actively seek out the caregiver is adaptive and evolutionarily conserved. However, continued activation of this distress system after an extended period of time, when there is little likelihood for reuniting with the caregiver, could expose the young animal to predators and exhaustion. Thus a mechanism for terminating the separation-distress response is also necessary and would be evolutionarily conserved as well. Watt & Panksepp propose that this separation-distress shutdown system, however, is vulnerable to hypertrophy and excessive activation, providing a biological substrate for depression.

With ongoing phylogenetic development the separation-distress shutdown (SDS) system likely came to serve additional but related functions—for example, the inhibition of protest to other types of losses such as losses of social attachment, social status, comfort, other rewards, and possibly even other disruptions to homeostasis such as those caused by physical illness or chronic pain. Thus the system could be triggered by the range of stressors known to precipitate depression. Once activated, it would close down seeking-behaviors a