Evolutionary Perspectives
Daily life is full of emotions, from the pleasures of happiness and love to the pains of worry, frustration, sorrow, and anger.
While we may take them for granted, our feelings are actually an extraordinary evolutionary achievement, as remarkable in their own way as language and logic.
Animals have emotions, too, as Darwin observed in his book, The Expression of Emotions in Man and Animals, in 1872. But consider the apparent emotions in a spectrum of animals, from – say – snakes and lizards, to squirrels, dogs, and monkeys, and then to human beings. There is a direct correlation between the complexity of social life of a species and the range and depth of the emotions of its members. Because our relationships are so layered, nuanced, enduring, and plain messy, humans have the greatest emotional range of any animal.
In our species, emotions serve many functions. They arouse our interest and tell us what to pay attention to. They motivate approach strategies through pleasant feelings and motivate avoidance or attack strategies through unpleasant ones. They enable us to share states of mind with other members of our family, tribe, or nation – and to signal or detect important states of mind such as fear, disgust, anger, or erotic interest. They bond children and parents, lovers and friends.
Emotions join us in common cause with other people, whether it’s chatting companionably while gathering nuts and berries on the African savanna 100,000 years ago or circling with spears around a woolly mammoth in Siberia 80,000 years later – or it’s cheering our football team to victory . . . or exulting, alas, while watching our nation’s missiles strike an enemy target.
More subtly, emotions make us known to ourselves. Flowing through the field of awareness – perhaps arising, actually, as a modification of awareness – emotions signal the deeper underlying movements of mental activity.
Which reflects, of course, the underlying movements of neurological activity.
Emotion in the Brain
The major brain regions that support emotional processing include the limbic system – particularly the hippocampus, amygdala, and hypothalamus – and the prefrontal cortex, anterior cingulate cortex (ACC), nucleus accumbens, and insula. Technical note: there are two hippocampi, one in each hemisphere of the brain; the same for the two amygdalae, ACCs, and insulae. Following common practice, we’ll mainly use the singular form.
By the way, as an interesting evolutionary detail, the limbic system seems to have evolved from the olfactory (scent) neural circuitry in the brain developed by our ancient mammal ancestors, living around 180 million years ago. They seem to have used their advanced sense of smell to hunt at night, while those cold-blooded reptiles were snoozing – and easier prey.
The conscious experience of emotion is just the top story – the penthouse floor – resting on many layers of neurological activity, both the firing of very complex and intertwining neural circuits and the tidal flows of neurotransmitters and hormones such as dopamine, serotonin, and oxytocin.
Here’s a brief summary of each of these brain regions and its apparent role in emotion:
Hippocampus
This vaguely sea-horse shaped region helps to store the contexts, especially visual-spatial ones, for important experiences, such as the smell of a predator . . . or the look of an angry parent. This region is necessary for forming personal memories of events and is unfortunately damaged over time by the cortisol released by chronic stress (especially high, or even traumatic, levels of stress).
Amygdala
Connected to the hippocampus by the neural equivalent of a four-lane superhighway, this small, almond-shaped region is particularly involved in the processing of information about threats. The subjective awareness of a threat comes from the feeling tone of experience when it is unpleasant (distinct from pleasant or neutral). When it perceives a threat – whether it’s an external stimulus, like a car running a red light, or an internal one, such as suddenly recalling an impending deadline – the amygdala sends a jolt of alarm to the hypothalamus and other brain regions. It also triggers the ventral tegmentum in the brain stem, to send dopamine to the nucleus accumbens (and other brain regions) in order to sensitize them all to the “red alert” information now streaming through the brain as a whole.
Hypothalamus
This is a major switchboard of the brain, and it’s involved in the regulation of basic bodily drives such as thirst and hunger. When it gets a “Yikes!” signal from the amygdala, it tells the pituitary gland to tell the adrenals to start releasing epinephrine and other stress hormones to get the body ready for immediate fight-or-flight action. Keep in mind that this activation occurs not just when a lion jumps out of the bushes; it happens chronically: in rush-hour traffic and multi-tasking, and in response to internal mental events such as pain or anger. (For more on the stress-response and what you can do about it, see the Wise Brain Bulletin, Volume 1, #5 and #6.)
Prefrontal Cortex (PFC)
If you whack your self on the forehead, mini-shock waves reverberate through the PFC, which is “pre” because it is in front of the frontal cortex. The PFC is centrally involved in anticipating things, making plans, organizing action, monitoring results, changing plans, and settling conflicts between different goals: these are called the “executive functions,” and if the brain is one big village, the PFC is its mayor.
Where emotion is concerned, the PFC helps one foresee the emotional rewards (or penalties) of different courses of action. The PFC also inhibits emotional reactions; many more nerve fibers head down from the PFC to the limbic circuitry than in the other direction. The left PFC plays a special role in controlling negative affect and aggression: stroke victims whose left PFC is damaged tend to become more irritable, distraught, and hostile (the same happened for the unfortunate and famous Phineas Gage, the engineer who suffered an iron bar through his forehead in a mining explosion). On the other hand, differential activation of the left PFC is associated with positive emotions – and years of meditation practice!
Anterior Cingulate Cortex (ACC)
This sits in the middle of the brain, centrally located for communication with the PFC and the limbic system. It monitors conflicts between different objects of attention – Should I notice the bananas in this tree or that snake slithering toward me? Should I listen to my partner or focus on this TV show? – and flags those for resolution by the frontal lobes. Therefore, it lights up when we attend to emotionally relevant stimuli or sustain our attention to important feelings – inside ourselves and other people – in the face of competing stimuli (e.g., trying to get a sense for what’s really bugging a family member underneath a rambling story and other verbiage).
Nucleus Accumbens
In conditions of emotional arousal – especially fear-related – the accumbens receives a major wake-up call of dopamine from the tegmentum, which sensitizes it to information coming from the amygdala and other regions. Consequently, the accumbens sends more intense signals to the pallidum, a relay station for the motor systems, which results in heightened behavioral activity. This system works for both negative and positive feelings. For example, the accumbens lights up when a person with an addiction sees the object of his or her craving.
Insula
Deeply involved in interoception – the sensing of the internal state of the body (e.g., gut feelings, internal sensations of breathing, nausea) – the insula lets you know about the deeper layers of your emotional life. And it is key to sensing the primary emotions in others, such as fear of pain, or disgust.
Want to Know More?
Keep reading to learn about the machinery of upset and what we can do about it to cultivate peace of mind.
This is Part One of the three-part “Peace of Mind” series: Part Two: Why We Get Upset.
Part Three: Cultivating Peace of Mind.
