What goes on in the brain when everything seems to be going wrong, or - for that matter - right? Say, when you feel fearful rather than motivated? Last week, in a piece entitled Beyond the DSM, we reviewed how the NIMH is orienting its research toward learning more about how brain circuitry affects behavior and emotions. Part of this includes investigating brain systems according to five (admittedly arbitrary) distinct domains. In 2011, experts gathered into five separate NIMH workshops, one for each domain. The NIMH website offers summaries of what went on at these sessions. Keep in mind, nothing is set in concrete,
Over the next two or three weeks, we will explore these domains. We'll start by investigating the first two: negative valence systems and positive valence systems.
Negative Valence Systems
Think of how we behave when our environment turns on us. When the brain is working right, the responses can be considered adaptive and appropriate. Fear, for instance, promotes behaviors (including aggression) that protect us from immediate perceived danger. Anxiety, on the other hand, is more about the brain's response to a threat that is distant and ambiguous or low in probability.
A sustained threat, on the other hand, tends to result in different patterns of behavior while frustration follows from our inability to obtain a positive reward. Finally, there is loss, which results in grief.
There is considerable overlap as to how the brain responds to what goes on around us, but there also appears to be different stuff happening in the circuitry. For instance, immediate threat sets off the brain's amygdala while potential harm (calling for vigilance) has been shown to be related to activation in bed nucleus in a neighboring area of the brain.
Then there is the HPA axis, which is associated with the fight or flight response. But it can also be activated by positive stimuli (nothing is ever simple). Technically, the HPA axis is not a neural circuit, though it is regulated by neural factors. The HPA axis involves the "reaction" part of a reaction-regulatory-recovery spectrum. Think of various neural circuits as working to maintain homeostasis. The HPA axis primes us for fight or flight, but we can't stay this way forever.
Positive Valence Systems
Now think how we behave when we sense the prospect of reward and anticipate the satisfaction of achievement to how we respond to reward to how our behavior is conditioned by the expectation of reward. What goes on, for instance, when we weigh the work we need to put into a project vs its potential pleasure pay-off? If one is feeling anhedonic (loss of the ability to experience pleasure), one is obviously not motivated to put in the effort.
Stuff to Think About
Note that by thinking in terms of negative and positive valence systems, we are forced to rethink DSM depression, anxiety, and mania. A depression, in short, is not a depression. It may be the result of a failure of the HPA axis failing to reset to normal. It may be the result a dopamine traffic jam in the pleasure-reward circuits of the ventral striatum. It could be the reverse - the dopamine is flowing too freely (voila, mania), or maybe not freely enough in the other direction, to inhibit what's going on in the limbic system (voila, mania again).
Don't worry if all this is appears way too complex for you. It is also way too complex for the experts. That's why they are gathering in places like the NIMH to scratch their heads and talk amongst themselves. The answers are a long way off. But at least they are asking the right questions.