The basis of fear

In this WiPhi video, we will examine some common ideas about the neuroscience of fear. Imagine you are in a new city. You’re heading back to your hotel after dinner. It's dark. It's late. Because there is hardly anyone around, you're on alert. Suddenly, you hear a loud noise from behind you, and it feels like your heart just jumped out of your chest. The hairs at the back of your neck stand up, your heart is beating fast, your hands have become clammy, and you are ready to run. You are in a state of fear. This is a common experience. What is the neurobiological basis for fear? What is going on in our brains when we have this experience? The prevailing view is that fear stems from the amygdala, an almond-shaped cluster of cells in the temporal lobe that detects the emotional salience of things. A lot of this has to do with the pioneering work done by the neuroscientist Joseph LeDoux. In LeDoux’s own words, the amygdala is the “hub” of fear. But what does it mean to say that the amygdala is the hub of fear? And is that right? First, when LeDoux says that, he doesn’t mean that fear stems just from the amygdala. Mental activity, including our emotions, stem not from specific brain areas, but rather complex brain systems, comprising many neural circuits, extending along several regions of the brain. So when LeDoux described the amygdala as being the hub of fear, what he really meant was that fear is caused by activity in neural circuits which involve the amygdala. In other words, activity in the amygdala is a crucial part of the neural activity in the brain that generates fear. For a long time, this view has gone unchallenged. A quick internet search for the word ‘fear’ generates countless articles claiming that fear stems from the amygdala. But this idea has been challenged by none other than LeDoux himself. According to LeDoux, a lot of his work has been misunderstood. In fact, he claims that he wasn’t studying the neural basis for fear at all, but something else, namely the neural underpinnings of the threat response. What is going on? LeDoux’s original research involved finding out what happens in the brains of rats when facing threats. He found that their physiological and behavioral responses when exposed to threatening stimuli were correlated with activity in neural circuits involving the amygdala. This was the original basis for saying that the amygdala is the ‘hub’ of fear. But as LeDoux now acknowledges, to say that the amygdala is responsible for fear based on this research is misleading. The reason for this is that the word ‘fear’ in everyday use is different from that in neuroscience. When neuroscientists talk about fear, they mean the sorts of changes our bodies undergo when we are exposed to threatening stimuli. By contrast, when we typically talk about fear, we don’t just mean these sorts of changes. Our common understanding of fear involves a particular sort of subjective feeling. When we say someone is experiencing the emotional state of fear, we don’t just mean that they are disposed to run away. Nor do we just mean that their body undergoes certain changes, like a racing heart, clammy hands, sweaty brow, and so on. We also mean that they feel fearful. There is something it is like to feel fearful, something that belongs to the subjective experience of the person experiencing fear. The conscious feeling associated with the experience of fear is what philosophers call its ‘phenomenal character’. And the neural circuits responsible for how our bodies respond to threats might not be the same circuits that underpin the conscious feeling of fear. In fact, according to some of the latest neuroscientific work done on emotion, while the amygdala-based circuitry plays a major role in controlling how our bodies respond to threat, your brain needs to do a lot more than that to generate the conscious feeling of fear. More technically, LeDoux thinks that various kinds of physiological changes your body undergoes in response to threat involves activity in the evolutionarily ancient subcortical regions of the brain, which includes your amygdala. But for LeDoux, that’s not enough to generate the conscious feeling of fear. This feeling arises from further activity in an evolutionarily newer part of the brain, namely the neocortex. So is the amygdala the hub of fear? Not according to LeDoux. For LeDoux, the amygdala is better seen as being the hub for the brain’s threat circuitry. But the threat response might occur below the level of conscious awareness. Whatever in the brain explains our experience of fear must explain why we experience the conscious feeling of fear. Now think back to when you felt afraid in that foreign city. It seems like your brain did two things. It activated the neural circuitry designed to respond to threats. It’s this circuitry that causes your heart to beat fast, your palms to get clammy, and for you to get ready to flee. But in addition, it also activated neural circuitry that enabled these responses to be experienced as fear. It is this extra work done by parts of your brain besides the amygdala that are responsible for your conscious feeling of fear. So next time someone says the amygdala is the part of the brain responsible for fear, ask them what they mean. By the word ‘fear’, do they mean the various bodily changes associated with threat? Or do they mean the conscious feeling of fear? What we’ve learnt is that the neural basis for these two things are most likely different. What do you think?