Fear and Loathing in the Human Brain

by Dr Andy Calder

Research addressing the brain regions involved in human emotion has expanded rapidly in recent years. This is, in part, due to the widening availability of new brain imaging technology, but also to a newfound interest in the idea that certain individual emotions may be served by separate brain systems. This latter theoretical position is at the heart of the idea that selected sets of so-called "basic" emotions with strong evolutionary histories constitute the foundations of human emotion. Although this concept has its origins in the work of Charles Darwin, it only really took off following the work of psychologists such as Silvan Tomkins, Paul Ekman, and Carol Izard in the 1960s and 70s. Prior to this, emotion research was dominated by the idea that all emotions were coded as values on a limited number of dimensions or scales coding more general emotional constructs, such as valence (how positive or negative an emotion is) and arousal (whether the emotion is associated with low arousal or high arousal). Similarly, early neurological accounts of emotion processing took a similar all-encompassing approach in which all emotions were processed by a circuit of interconnected brain structures known as the limbic system.

Two important findings of Ekman and his contemporaries that changed theories of emotion were studies demonstrating that certain emotions (happiness, sadness, anger, fear, and disgust) were associated with distinct facial signals, and that these were common to cultures throughout the world; observations that now constitute two of the defining features of basic emotions. A third posited feature was the idea that each basic emotion should be associated with a distinct (neuro)physiological signature, such as a particular brain circuit or a more peripheral body state response, including heart rate, or galvanic skin response (an index of lying in the famous lie detector test) and so on. Human evidence consistent with this third feature proved difficult to find; However, support was found in non-human biological studies by researchers such as Joe LeDoux and Jaak Panksepp.

It is of considerable interest, then, that work with humans over the last eight years has begun to identify that certain emotions may be coded by partially distinct brain systems as Ekman and his colleagues had predicted. This research has been aided greatly by recent advances in brain imaging technology that allows more precise localisation of the regions damaged in brain-injured patients, and identification of the areas of the brain that are activated in healthy individuals when they perform a psychological task. A large number of these studies have addressed the areas of our brain that are used to recognise emotion in others; in other words brain systems involved in recognising facial and vocal signals of emotion. Two emotions that have received considerable amount of attention are fear and disgust.

To date brain imaging technology and work with patients who have suffered brain injuries has shown that a small almond-shaped structure in the brain called the amygdala, plays a significant role in recognising facial and vocal expressions of fear. For example, my colleagues and I at Cambridge University studied a lady known as DR who underwent neurosurgery to relieve epilepsy that was resistant to pharmacological treatment. The cause of DR's epilepsy was her left and right amygdala, and the surgeon removed both structures in an attempt to reduce the frequency of her epileptic fits. Calder and colleagues demonstrated that DR showed an impaired ability to recognise fear, and to a lesser extent anger from facial and vocal expressions of emotion, whereas her recognition of other emotional expressions was normal. This showed that amygdala was important for recognising these emotions.

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