Book review of Joseph Ledoux

Joseph Ledoux:
THE EMOTIONAL BRAIN (Simon & Schuster, 1996)

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The weakness of Ledoux's important book on emotion is that he studies only one kind of emotion (fear) but draws conclusions about all emotions. This is, to say the least, a wild assumption: that all emotions use the same circuitry and the same processing as the emotion of fear. One would expect exactly the opposite, given that fear and, say, joy produce completely different "feelings" and behavior.

That said, his fundamental tenet is that the region of the brain called "amygdala" stores emotional memories. More precisely, the amygdala is the place where the brain decides whether to react or act. When we find ourselves in danger, first we "react" (we unconsciously apply one of the patterns of behavior that evolution has added to our repertory of survival strategies) and then we "act" (we make a conscious decision). Unconscious reaction occurs when information flows from the lateral amygdala to the central amygdala (and results in the typical behavior of fear, such as blood pumping, heart thumping, frantic breathing, sweating, pupil dilation). Conscious action occurs when information flows from the lateral amygdala to the basal amygdala (and results in retrieving memories from the neocortex). The transition from unconscious reacting to conscious acting is therefore a "switching" of the flow of information from the lateral amygdala to either the central amygdala or the basal amygdala. The pathway of conscious action is fundamentally unique to humans, whereas the pathway of unconscious reaction is largely shared by all mammals. There is a continuity between the emotional brain system of ancient mammals and humans.

Even before birth, the amygdala of a baby memorizes fear states (first of the mother, then of itself). At the same time, the amygdala retrieves and reenacts a fear state whenever a known context reoccurs. The amygdala stops performing the memory task when the child is about five years old, but continues to work as a template for fear states for the rest of the adult life. Unconscious fear memories are forever.

A critical finding was that information reaches the amygdala before the cortex. In fact, some stimuli may never reach the cortex at all. That is why we may react to a situation without even realizing what we are doing until well after we have done it.

Ledoux believes that emotion (the unconscious reaction) and cognition (the conscious action) are separate but interacting mental functions mediated by separate but interacting brain systems.

Ledoux believes that emotions are a prerequisite to consciousness, but consciousness requires more. It is in the working short-term memory that one becomes aware of one's own emotions. This area is localized in the lateral prefrontal cortex, which only exists in primates and is particularly large in humans.