Chapter 4 - Neurological and psychiatric aspects of emotion
Introduction
Terms such as feelings, emotions, and moods are frequently used in daily life without strict attention to their conceptual underpinnings. On the other hand, research in the neurosciences requires proper definitions of the above terms. The neuroscientist has to face questions such as, What constitutes an emotion? Are feelings necessary components of emotions? Are moods long-lasting emotions or different entities? Such questions have been addressed by philosophers, neuroscientists, and psychologists, but without definitive conclusions. What follows is a concise introduction to the concept of emotions and moods that will help to situate the chapter in its appropriate context.
Contemporary definitions of emotion depend on the perspective being used. Most of the philosophical tradition, from Aristotle to Wittgenstein, used an analytical approach and defined emotions as cognitions, feelings, or behaviors caused by specific agents that occur in a given context. For evolutionary biologists emotions are behavioral responses that promote human survival, whilst anthropologists consider emotions as patterns of feelings, cognitions, and behaviors related to social functions and determined mostly by culture. Neuroscientists conceptualize emotions as feelings, cognitions, and behaviors that result from activation in specific brain circuits (Roberts, 1988).
Some emotions consist mostly of feelings whilst others consist of specific behaviors which may or may not have social consequences. Feelings are sometimes considered as constituting the emotion, or as a somatic feature of emotions. Moreover, these somatic features may be just “inner feelings” or objective physiological attributes. Some emotions are characterized by specific facial expressions, whilst a nonspecific bodily arousal may be shared by different emotions. The behavioral expression of emotions may be either voluntary or involuntary. Some emotions consist of rational analysis producing feelings of pain or pleasure; some emotions are specific to given cultures whilst others are shared by most cultures. Finally, context plays a critical role for some emotions, providing the background against which the emotion may be correctly understood (Roberts, 1988).
The question also arises as to what are the differences between emotions and moods. Emotions have specific objects and causes (e.g., a snake is the object of fear, but the cause of fear is the knowledge that a snake bite may be dangerous), whilst moods are considered to lack objects or causes (e.g., free-floating anxiety). Emotions are usually short-lasting events, whilst moods are defined as long-term dispositional states of mind which are related to typical behaviors (e.g., depression usually features sad mood, changes in sleep, appetite, and energy, and anhedonia) (Damasio, 1999). Nevertheless, the conceptual border between emotions and moods is not sharp. For instance, depression may fit the definition of emotion when it sometimes has an object and a cause (e.g., bereavement depression), whilst an individual with an anxious personality is predisposed to bouts of fear and worrying (Bennet and Hacker, 2003).
Research carried out during the past 30 years has consistently demonstrated a high frequency of emotional and mood disorders among patients with acute or chronic neurological conditions. In fact, psychiatric disorders following neurological disease are not only a source of suffering for patients and their caregivers, but are also related to worse motor and cognitive outcomes, increased disability, and higher mortality.
The first part of this chapter will review the frequency, correlates, longitudinal evolution, and treatment of some of the most frequent psychiatric and emotional conditions in neurological disorders, namely depression, apathy, and loss of insight (anosognosia). These conditions will be discussed for common acute and chronic neurological conditions, including Alzheimer's disease (AD), stroke, Parkinson's disease (PD), and traumatic brain injury (TBI). The second part of the chapter will discuss the neurology of emotion from a brain–behavior relationship perspective. The review will focus on neuroanatomical structures that have been well documented to play critical roles in emotional processing, including various right hemisphere structures, the amygdala, the ventromedial prefrontal cortex (vmPFC), and the basal ganglia.
Section snippets
Depression
The first challenge is how to diagnose depression in neurological disorders when the putative symptoms of depression may be related to cognitive and physical aspects of the neurological condition. Four different strategies have been used to diagnose depression in neurological disorders. The inclusive approach is currently the most favored one, and consists of diagnosing depression based on symptoms which may or may not be related to the medical illness (Marsh et al., 2006). The exclusive
Apathy in neurological disorders
The term “apathy” is used to refer to a syndrome characterized by poor motivation, as manifested by reduced goal-directed cognition, behavior, and emotion. Already in the 19th century the term “apathy” was used to refer to states of physical and psychological hypoactivity. Currently, apathy is considered one of the most common behavioral changes among patients with neurological disorders. Marin (1991) defined motivation as “the direction, intensity and persistence of goal-directed behavior,”
Loss of insight
Loss of insight was described by Babinski (1918) in 2 patients with a left hemiplegia who denied their motor deficit. He termed this condition “anosognosia,” and coined the term “anosodiaphoria” to refer to patients who would acknowledge their motor deficit but would show indifference about their condition. Loss of insight is a well-known consequence of TBI, especially after orbitofrontal lesions, and is usually accompanied by a disinhibition syndrome (Starkstein et al., 1988b). Anosognosia is
Right hemisphere structures
There has been a long-standing emphasis on right hemisphere structures as being especially important for emotional processing, and both clinical and experimental studies have supported the conclusion that the right hemisphere is preferentially involved in processing emotion in humans and other primates. This may reflect or be associated with some of the underlying hemispheric specializations typically associated with the right hemisphere (it should be noted that, for the sake of exposition, we
Conclusions and future directions
The past 30 years have witnessed an exponential interest in the neurological and psychiatric aspects of emotion. A variety of emotional disorders have been identified in both acute and chronic neurological disorders. Moreover, an increasing number of studies show a negative impact of emotional disorders upon the rehabilitation of neurological patients and the well-being of their respective caregivers. Future studies will validate specific diagnostic criteria for the various emotional problems
Acknowledgments
SES is supported by NHMRC 634412. DT is supported by NIDA R01 DA022549 and NINDS P50 NS19632.
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