Humans have a possibly unique ability to change their internal environment spontaneously. Everyone has experienced times when you were paying attention to something and you just drift off to muse over something, remember an event, or even disappear into your imagination. This can be fun, inconvenient or distressing, depending on the quality of your thoughts. Mind wandering enables you to imagine the future, relive the past or even place yourself in a world that only you can imagine.
The important thing to note about this retreat from the external world is that the content of your mind wandering is not necessarily tied to external stimulation. Instead, it is uniquely yours – built upon your experiences, desires, motivations and emotions (whether good or bad) and particularly upon your emotional regulation. You are responsible for the content of your internal musings, and this is what makes it range between a wonderful and life affirming retreat or a horrible, crippling place to be.
This chapter will spend time detailing the way the healthy human brain operates before we move on to how altered brain function might contribute to mental distress.
Humans are emotional beings and yet it cannot be said that we fully understand how emotions and feelings operate. Most textbooks, whether cognitive or biological, sometimes convey the impression that emotions are felt one at a time, and yet we know from our own experience that this is not the way it is. You can love your child, for example, but at the same time be irritated that s/he have trodden mud over your carpet; or you can be enjoying a night out at the cinema but be crying because it is a sad film. Emotions are multifaceted and to an extent uncontrollable, however, we need them. The study of people without emotions (Damasio, 1994) reveals that behaviour such as decision making needs emotional input to be rational. Emotions and the ability to assess our own emotional state, and that of others, help us to interact with other humans. Discriminating the emotions of others, such as when someone is angry or sad, helps us to avoid potentially difficult social situations. This has evolved into a field in its own right as the study of emotional intelligence (Salovey and Mayer, 1990; Mayer and Salovey, 1993).