The limbic system for Emotion

By now it should be clear that emotions have biological and evolutionary bases and involve both the CNS and the ANS. Although subcortical brain mechanisms are implicated in emotion – from the brain stem to the hypothalamus, thalamus and amygdala – cortical structures play an executive role. Animals with their cortex removed but with intact hypothalamus and thalamus show violent (sham) rage (Dusser de Barenne, 1920). Sham rage is so called because a weak stimulus can cause a release of autonomic responses (such as sweating and increasing blood pressure) that are normally only elicited by strong stimuli, and the anger is not directed at any one particular entity. Electrical stimulation of the hypothalamus can also produce such rage. Subcortical structures alone, however, do not provide the physiological mediation of emotion. This is provided by the limbic system of the cortex, with its extensive connections to the subcortex. The long history of research in these regions includes work by MacLean (1954, 1957, 1993). This work suggests that the limbic system, throughout its evolution, has helped to refine the emotional feelings that influence self-preservation. More recently, Panksepp (1981, 1989, 1991, 1992, 1993) made a very significant theoretical contribution to the physiology of emotion. He agrees that emotion is centred in the limbic system and has provided evidence for four, or possibly five, hard-wired emotion-mediating circuits. Panksepp is certain about the emotions of
i) expectancy, ii) fear, iii) rage and iv) panic,
although his evidence is not quite as convincing for the fifth, ludic (play) system. Interestingly, Panksepp’s approach is not solely neurophysiological but also considers the subjective or experiential. So, not only are there structural similarities between mammalian limbic systems across species, but Panksepp further uses subjective experience as a guide for distinguishing between those human brain states of emotion that appear also to be differentiated neurophysiologically.

Simultaneously, Le Doux (1999) demonstrated convincingly that much of the CNS work in relation to emotion is performed by the amygdala. Le Doux argues that the amygdala acts as an ‘emotional computer’, analysing any incoming information for its significance. In right-handed people, the right side of the brain, with which the amygdala has more extensive connections, is more associated with emotion than the left side. Le Doux argues that the connections between the amygdala and the thalamus may be especially relevant in the perception of emotion. In lefthanded people, it is likely that the converse holds – i.e. that thereare left hemisphere–amygdala connections. It should be apparent from the discussion presented above that the physiological investigation of emotion has added much to our current knowledge. We now turn to a consideration of the complementary cognitive perspective.