Is Sadness an Evolutionarily Conserved Brain Mechanism to Dampen Reward Seeking? Depression May Be a “Sadness Disorder”

Douglas Watt and Jaak Panksepp's article addresses two fundamental questions in behavioral neuroscience:

1. How is the protest phase of separation distress adaptively terminated?

2. What is the evolutionary purpose of depression?

Their innovative response is to use each question to answer the other. Separation distress is terminated by depression, and depression evolved to terminate separation distress.

In analyzing this appealing, if somewhat circular, argument, I will draw contrasts between it and a model addressing the same questions recently published by myself and John Mann (Freed & Mann, 2007), to which it bears many similarities, but from which it departs in several key aspects.

Freed and Mann suggest that the core problem in separation distress is the persistent incentive salience, or reward-value, of the missing love object. This incentive salience drives four key features of the protest phase: (1) attention toward reminders of the missing attachment, (2) yearning for the missing attachment, (3)motivation to seek out the missing attachment, and (4)crying behavior.

In our model, the opportunity cost of protest is its most serious downside. While a period of heightened incentive salience may adaptively promote reunion with a missing object, attention/yearning/seeking/crying comes at the expense of pursuing other strategies toward adaptive fitness. At a certain break-point the opportunity cost of protest becomes too high relative to other avenues toward regaining function, and, for adaptive fitness to be maximized, it must be down-regulated.

As in the Watt-Panksepp model, Freed and Mann suggest that the despair phase of separation distress is a likely candidate for facilitating the downregulation of protest. But which parts of despair are targeting which aspects of protest? Rather than suggest that the entire despair phase performs some function with respect to the entire protest phase, we focus on the core “positive symptom” of despair—sadness—and its relationship to the