The complexity of emotions is vast, but during the past few decades, progress in clarifying the neurological substrates has been enormous. This knowledge will have increasing consequences for the reconceptualization of foundational issues in biological psychiatry. In deep subcortical regions of the mammalian brain, there exist a variety of genetically prescribed circuits that mediate basic (instinctual) emotional behaviors. As discussed in this chapter, and several others in this text, there are many reasons to believe that various basic affective experiences are dependent on the activities of such neural systems.
Textbook of Biological Psychiatry. Edited by Jaak Panksepp Copyright © 2004 by Wiley-Liss, Inc. ISBN: 0-471-43478-7
Emotions have a variety of attributes, including autonomic-bodily, behavioral-expressive, cognitive-learned, and affective-experiential components. This last aspect—the subjective intensity and valence of our diverse emotional experiences—makes it a topic of foremost importance for psychiatry. Without affective feelings, it is hard to imagine that the concept of emotion would exist. People with psychiatric problems are commonly troubled by the chaotic, often misplaced and undesirable affective intensity of their lives. The success of most psychiatric interventions is premised on their ability to facilitate affect regulation.
Although there has now been enormous progress in imaging how the brain processes emotional information, until quite recently the fundamental neurobiological nature of affective experience remained totally mysterious. Substantial progress has now been made on imaging key brain areas that help elaborate affect in humans as well as neuroanatomical and neurochemical circuits that mediate core emotional responses in animals. Investigators are also learning how to blend information from the two sources. Most human brain imaging studies presently provide anatomical correlates that may or may not reflect causal processes. On the other hand, animal brain research can help decipher the details of the underlying causal issues in ways that ethical human research could never achieve. Through a balanced interplay of human and animal psy-chobiological research, a level of knowledge can be achieved that neither approach, alone, could achieve. The translation of knowledge among species will depend on the degree of evolutionary homology in the underlying substrates (Chapters 16, 20, and 21).
The assumption that animals also have affective experiences when they exhibit instinctual emotional behaviors can yield precise working hypotheses concerning the neural nature of basic affects that, after development and deployment of appropriate neuropharmacological tools, can be rigorously evaluated in the human species. For instance, various chemistries identified through preclinical animal research can already guide the selection of new pharmacological targets to be evaluated in humans (e.g., Chapter 21). Unfortunately, this level of evolutionary continuity is not yet widely accepted. Since the subjective-experiential aspects of emotions cannot be observed directly in either animals or humans, the study of emotional feelings has lagged behind the science of emotional behaviors. Indeed, some investigators have been eager to conceptually separate the two, but we doubt if that semantic maneuver is ontologically justified. Affective feelings may be closely linked to, indeed interpenetrant with, the neurodynamics of instinctual emotional systems in action.
In sum, a new neuroscience of emotions is emerging rapidly. Because of limited space, we shall not cover historical issues. Suffice it to say that the modern study of brain emotional systems qualifies and brings into question earlier peripheralist views that attributed emotions to visceral changes or cognitive-type propositional attitudes and appraisals that we acquire through life experiences. Even though it is still accepted that peripheral and cognitive factors modulate core emotional processes in many important ways, central brain mechanisms are taking center stage in modern analyses of emotions. While changes in the activity of the autonomic nervous system are important for the modulation of emotional intensity and specific types of bodily feelings that accompany emotions, the affective nature of our minds is not simply a result of the readout of bodily arousal by higher cortico-cognitive systems of the brain as has been long assumed in psychology (e.g., the classic James-Lange perspective). In fact, there are reasons to believe that brain emotional processes are very capable of modulating peripheral organ responses via direct neural as well as many hormonal routes, including direct secretions from the brain into the bloodstream (Kastin et al., 1999).
It is now generally recognized that specific brain circuits, highly interactive with the visceral and skeletal-muscular systems, are essential for emotions. The brain's emotional infrastructure is concentrated in midline, visceral regions of the brain (Papez, 1937) that were enshrined in the concept of the limbic system (MacLean, 1990). Although the utility of the limbic concept has been debated vigorously (e.g., Cory and Gardner, 2002; LeDoux, 1996), it is fair to say that most of the brain imaging work on affective processes (albeit not related cognitive information processing) affirms that the limbic concept correctly identifies the general neuronal territories where both the affects and emotional behaviors are elaborated in the mammalian brain.
The basic emotions come in various dynamic forms and certainly include core instinctual processes such as anger, fear, eager anticipation, joy, sadness, and playfulness (see Table 21.1, which also highlights the key neurochemistries identified so far). All of these complex brain functions can be linked to major psychiatric disorders in fairly straightforward, albeit speculative, ways (Table 1.1). These action-feeling systems allow all species of mammals to respond to the world in characteristic ways; and, to the best of our current knowledge, the underlying neurochemical controls have been evolutionarily conserved, in principle, across higher vertebrates. Within the higher limbic and neocortical reaches these systems interact with cognitive processes, considerably more variable among species, which yield layers of epigenetic complexities where cross-species comparisons will never be as robust.
The cortical-subcortical interactions create a special richness for human emotional life, as well as existential forms of emotional turmoil unknowable to other species. The various socially derived emotions include a vast number of variants—including shame, guilt, jealousy, envy, embarrassment, pride and many others—that provide a special subtlety to human emotional life. Although age-old debates continue over how our moods and emotions are best conceptualized (see Ekman and Davidson, 1994), the realization that neural criteria will be essential for defining such affective experiential states is now widely accepted, and increasingly so among even those mind sciences traditionally not accustomed to thinking in neural terms. The possibility of imaging such processes in the human brain, using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) technologies, has helped trigger the "affect revolution" that is currently sweeping across the mind sciences.
The aim of this chapter is to provide an overview of how emotions are generated within the brain. Since research on humans and research on animals presently provide rather distinct lines of evidence, they will be summarized separately. First we will summarize human data as derived from now classic studies of brain-damaged individuals, followed by a summary of evidence from modern brain-imaging approaches. Then we provide a synopsis of conclusions to be derived from animal brain research, and an attempt to blend these approaches into a coherent whole.
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