Work on threat response, anxiety, and emotions As explained in his 1996 book,
The Emotional Brain, LeDoux developed an interest in the topic of emotion through his doctoral work with Michael Gazzaniga on split-brain patients in the mid-1970s. Because techniques for studying the human brain were limited at the time, he turned to studies of rodents where the brain could be studied in detail. He chose to focus on a simple behavioral model,
Pavlovian fear conditioning. This procedure allowed him to follow the flow of information about a stimulus through the brain as it comes to control behavioral responses by way of sensory pathways to the
amygdala, and gave rise to the notion of two sensory roads to the amygdala, with the "low road" being a quick and dirty subcortical pathway for rapid activity behavioral responses to threats and the "high road" providing slower but highly processed cortical information. His work has shed light on how the brain detects and responds to threats, and how memories about such experiences are formed and stored through cellular, synaptic and molecular changes in the amygdala. A long-standing collaboration with NYU colleague Elizabeth Phelps has shown the validity of the rodent work for understanding threat processing in the human brain. LeDoux's work on amygdala processing of threats has helped understand exaggerated responses to threats in anxiety disorders in humans. For example, studies with Maria Morgan in the 1990s implicated the
medial prefrontal cortex in the
extinction (psychology) of responses to threats and paved the way for understanding how exposure therapy reduces threat reactions in people with anxiety by way of interactions between the medial prefrontal cortex and the amygdala. Work conducted with Karim Nader and Glenn Schafe triggered a wave of interest in the topic of
memory reconsolidation, a process by which memories become labile and subject to change after being retrieved. This led to the idea that trauma-related cues might be weakened in humans by blocking reconsolidation. Studies with Marie Mofils, Daniela Schiller and Phelps showed that extinction conducted shortly after triggering reconsolidation is considerably more effective in reducing the threat value of stimuli than conventional extinction, a finding that has proven useful in reducing drug relapse in humans.
Difference between threat response and emotions In 2012 LeDoux emphasized the value, when discussing brain functions in animals, of using terms that are not derived from human subjective experience. The common practice of calling brain circuits that detect and respond to threats "fear circuits" implies that these circuits are responsible for feelings of fear. LeDoux has argued that so-called Pavlovian fear conditioning should be renamed Pavlovian threat conditioning to avoid the implication that "fear" is being acquired in rats or humans. In 2015 he emphasised the notion of survival functions mediated by survival circuits, the purpose of which is to keep organisms alive (rather than to make emotions). For example, defensive survival circuits exist to detect and respond to threats, and can be present in all organisms. However, only organisms that can be conscious of their own brain's activities can feel fear. Fear is a conscious experience and occurs the same way as any other kind of conscious experience: via cortical circuits that allow attention to certain forms of brain activity. He argues the only differences between an emotional and non-emotion state of consciousness are the underlying neural ingredients that contribute to the state. These ideas and their implications for understanding the neural foundations of pathological fear and anxiety are explained in his 2015 book,
Anxious, where he writes: "Fear and anxiety are not biologically wired... They are the consequence of the cognitive processing of nonemotional ingredients." In 2018 he wrote that the
amygdala may release hormones due to a trigger (such as an innate reaction to seeing a snake), but "then we elaborate it through cognitive and conscious processes". He differentiated between the defence system, which has evolved over time, and emotions such as fear and
anxiety. He points out that even simple organisms such as bacteria move in response to threats; "It's in the brain to allow an organism, whether it be a bacterium or a human, to detect and respond to danger. ... It's not in the brain to create feelings like fear and
anxiety."
Lisa Feldman Barrett takes a similar view. == Awards and professional recognition ==