Emotions

Emotions

EMOTIONS 



Emotion: refers to positive or negative feelings that are produced by particular situations. An emotional response consists of : 1. 2. 3.

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Behavioural Autonomic Hormonal components

These components are controlled by separate neural structures and systems.

The Amygdala  The

amygdala plays a special role in physiological and behavioral reactions to objects and situations that have special biological significance, such as those that warn of pain or other unpleasant consequences or signify the presence of food, water, salt, potential mates or rivals, or infants in need of care.

amygdala  The

amygdala is located within the temporal lobes. It consists of several groups of nuclei, each with different inputs and outputs and with different functions It has been twelve regions, each containing several subregions. The key area involved in emotions is the central nucleus.

central nucleus (CE).  The

central nucleus projects to regions of the hypothalamus, midbrain, pons, and medulla that are responsible for the expression of the various components of emotional responses.  activation of the central nucleus elicits a variety of emotional responses: behavioral, autonomic, and hormonal.

central nucleus (CE).  The

central nucleus of the amygdala is the single most important part of the brain for the expression of emotional responses provoked by aversive stimuli. When threatening stimuli are presented, both the neural activity of the central nucleus and the production of Fos protein increase.

 Damage

to the CE (or to the nuclei that provide it with sensory information) reduces or abolishes a wide range of emotional behaviors and physiological responses.

 After

the CE has been destroyed, animals no longer show signs of fear when confronted with stimuli that have been paired with aversive events.  They also act more tamely when handled by humans, their blood levels of stress hormones are lower, and they are less likely to develop ulcers or other forms of stress-induced illnesses.

 In

contrast, when the CE of the amygdala is stimulated by means of electricity or by an injection of an excitatory amino acid, the animal shows physiological and behavioral signs of fear and agitation and long-term stimulation of the central nucleus produces stress-induced illnesses such as gastric ulcers .

 The

CE of the amygdala is particularly important for aversive emotional learning. We learn that a particular situation is dangerous or threatening, therefore once the learning has taken place, we will become frightened when we encounter that situation. Our heart rate and blood pressure will increase, our muscles will become more tense, our adrenal glands will secrete epinephrine, and we will proceed cautiously, alert and ready to respond.

 One

of the earliest studies observed the reactions of people who were being evaluated for surgical removal of parts of the brain to treat severe seizure disorders. These studies found that stimulation of parts of the brain,e.g. the hypothalamus, produced autonomic responses that are often associated with fear and anxiety but that only when the amygdala was stimulated did people also report that they actually felt afraid.

amygdala  Lesions

of the amygdala decrease people's emotional responses. People with lesions of the amygdala showed impaired acquisition of a conditioned emotional response.  Damage to the amygdala also interferes with the effects of emotions on memory. Alzheimer's patients memory of a frightening event (earthquake) was inversely correlated with amygdala damage: The more a patient's amygdala was degenerated, the less likely it was that the patient remembered the earthquake.

 The

amygdala plays a role in recognition of facial expressions of emotions;  lesions of the amygdala disrupt this ability, and PET scans show increased activity of the amygdala while the subject is engaging in this task.

 Neural  The

Control of Aggressive Behavior.

activity of the brain stem circuits appears to be controlled by the hypothalamus and the amygdala, which also influence many other species-typical behaviors( hissing , striking, posturing). And, of course, the activity of the limbic system is controlled by perceptual systems that detect the status of the environment, including the presence of other animals.

Role of the Prefrontal Cortex  The

analysis of social situations involves much more than sensory analysis; it involves experiences and memories, inferences and judgments. These skills are not localized in anyone part of the cerebral cortex, but the right hemisphere is more important than the left and a region of the prefrontal cortex, the orbitofrontal cortex plays an important role.

Orbitofrontal Cortex

Anger & Aggression  The

fact that the orbitofrontal cortex plays an important role in the control of emotional behavior is shown by the effects of damage to this region. (1800s:- Phineas Gage, Before his injury he was serious, industrious, and energetic. Afterward, he became childish, irresponsible, and thoughtless of others)  His accident largely destroyed the orbitofrontal cortex.

Thus, moral judgments appear to be guided by emotional reactions and are not simply the products of rational, logical decision making processes and that the prefrontal cortex plays a role in these judgments.

Hormonal Control of Aggressive Behaviour (MALES)  Inter-male

aggressiveness begins around the time of puberty, which suggests that the behavior is controlled by neural circuits that are stimulated by androgens.  Castration reduced aggressiveness and that injections of testosterone reinstated it.

Hormonal Control of Aggressive Behaviour (MALES)  Males

readily attack other males but usually do not attack females. Their ability to discriminate the sex of the intruder appears to be based on the presence of particular pheromones.

Hormonal Control of Aggressive Behaviour (FEMALES)  Aggression

between females, like aggression between males, appears to be facilitated by testosterone.  Female rats are ovariectomized and then given them daily injections of testosterone, estradiol, or a placebo for 14 days. The animals were then placed in a test cage, and an unfamiliar female was introduced. It was found that testosterone increased aggressiveness, whereas estradiol had no effect.