DOC-20241208-WA0004.

22 Central Control of Emotion - Motivation (Limbic system) ILOs By the end of this lecture, students will be able to 1. 1. Classify the major components of the limbic system 2. 2. Explain reinforcement functions of the limbic system. 3. 3. Specify functions of the hippoc...

22 Central Control of Emotion - Motivation (Limbic system) ILOs By the end of this lecture, students will be able to 1. 1. Classify the major components of the limbic system 2. 2. Explain reinforcement functions of the limbic system. 3. 3. Specify functions of the hippocampus and amygdala 4. 5. Discuss the role of limbic system in controlling human behavior. Introduction The limbic system is the part of the brain involved in our behavioural and emotional responses, especially when it comes to behaviours we need for survival: feeding, reproduction and caring for our young, and fight or flight responses. Limbic system controls emotional behaviour and the internal factors that motivate animals and people to adapt to a constantly changing external environment. Control of behavior is a function of the entire nervous system. The limbic system constitutes several cortical and subcortical strucures that interact together to mediate emotions. Control of emotions involve : a visceral sensory component caused by endocrine and autonomic stimuli (a ‘gut feeling’), a motor component involving the facial muscles to communicate the pleasantness or unpleasantness of the situation to others, a cognitive–evaluative component to consciously assess the situation. The cortical structures are formed of a band of primitive cortical tissue that encircles the upper brainstem and include : the cingulate gyrus the parahippocampal gyrus. The subcortical structures include : thalamus, the hippocampus, he hypothalamus and the amygdala. The limbic system is also strongly linked to the oribitofrontal cortex. Figure 1: Structures of the limbic system James Papez demonstrated in 1937 that emotions involve a circuit comprising the hypothalamic mamillary bodies, thalamus, cingulate gyrus and Hippocampus. Disruption of this circuit leads to Emotional disturbance and inability to create memories. Page 1 of 5  Figure 2: Papez circuit Input to the limbic system comes from the association cortex areas, the olfactory cortex and the medial temporal lobe regions, and is ultimately passed on to the hypothalamus, which controls the endocrine system and the autonomic nervous system The limbic system is tightly connected to the prefrontal cortex, and together they funnel emotional input to the hypothalamus. The amygdala receives input from the hippocampus, olfactory cortex and temporal lobe association cortex. Its main outputs are to the septal nucleus and hypothalamus. Figure 3: connections of the limbic system There is frontal lobe asymmetry in regard to emotional processing. Activation in the LEFT prefrontal regions may be part of a mechanism that inhibits ‘negative’ affect (e.g. sadness and disgust). Conversely, the RIGHT prefrontal regions may inhibit positive emotions (e.g. happiness). People with increased left prefrontal activity are described as more ‘optimistic’ and more adept at minimizing negative emotions. Lesions of the left prefrontal neocortex are more likely to be associated with depression than lesions in the homologous location in the right hemisphere. During the Wada test, when the left hemisphere is temporarily anaesthetized, patients report negative changes in mood (e.g. sadness). Page 2 of 5 Specific functions of areas of limbic system ▪ Amygdala It is a collection of subnuclei in the medial temporal lobe. 1. The amygdala is necessary for emotional memories ( fear ). 2. Processing distressing stimuli related to threat (fight and flight ). The amygdalae are involved in detecting and learning what parts of our surroundings are important and have emotional significance. 3. Emotional responses to olfactory stimuli, Figure 4: The amygdala 4. other emotions (empathy). 5. Recognizing the emotions indicated by other peoples’ facial expressions. ▪ Stimulation of amygdala--→ FEAR and anxiety or euphoria Example: This is the structure that is responsible for the feelings of fear or dread when you are walking home late at night and hear footsteps behind you ▪ Damage to amygdala ---→not common but when done experimentally leads to inability to perceive situations as dangerous. Bilateral temporal lobectomy in monkeys produced a dramatic effect on the animals’ responses to fearful situations. The animal has bizarre behavioural abnormalities sucha as oral exploration of all objects, hypermetamorphosis (a compulsion to touch everything, and place each found object into the mouth), altered and increased sexual behaviour and emotional changes, including fearlessness and decreased facial expressions usually associated with emotion also been found in humans with temporal lobe lesions. In addition to oral tendencies and hypersexuality, people appear to have ‘flattened’ emotions. ▪ Hippocampus Hippocampus is involved in the production of longterm memories and the recall of such information. Example: The hippocampus allows humans to compare the conditions of a present situation, such as danger, with similar past experiences, in order to decide which is the best option to guarantee survival. Figure 5: The hippocampus Bilateral damage to the hippocampi impairs the formation of new memories, and nothing can be retained; information is soon forgotten. The hippocampus is also damaged in disease states such as dementia and epilepsy, and is a pathological hallmark of rabies. ▪ Hypothalamus Regulates the physical response to emotions through controlling the endocrine and autonomic nervous systems. Additionally in expressions of emotions: stimulation of the of lateral hypothalamus (rage center) crates a feeling of rage and anger while stimulation of the ventromedial nucleus creates placidity. ▪ Anterior cingulate gyrus The anterior cingulate gyrus communicates between the prefrontal cortex and subcortical areas of the limbic system. The anterior cingulate is also part of a network that mediates motivation. The anterior cingulate is mainly involved in the mediating: Page 3 of 5  1. Ethics 2. Moral emotions (processing) 3. Impulsive behavior (control) 4. Motivation : Motivation is the desire to do something due to some expected reward. Therefore, the reward and punishment centres constitute one of the most important of all the controllers of our bodily activities, our drives, our motivations. The major reward centres have been found to be located along the course of the medial forebrain bundle, especially in the lateral and ventromedial nuclei of the hypothalamus- nucleus accumbens. Less potent reward centres, are found in the septum, the amygdala, certain areas of the thalamus and basal ganglia. Stimulation of reward centers gives a rewarding sensation as satisfaction and enjoyment. The most potent areas for Punishment and escape tendencies have been found in the central gray area surrounding the aqueduct of Sylvius in the mesencephalon and extending upward into the periventricular zones of the hypothalamus and thalamus. Stimulation of punishment areas gives the sense of punishment as terror, pain, fear, defense and escape reactions. It is particularly interesting that stimulation in the punishment centres can frequently inhibit the reward and pleasure centres completely, demonstrating that punishment and fear can take precedence over pleasure and reward. ▪ Nucleus accumbens (Latin for nucleus adjacent to the septum) Each cerebral hemisphere has its own nucleus accumbens. The nucleus accumbens has a significant role in the cognitive processing of motivation, pleasure, and reward and hence has significant role in addiction. DOPMAINE triggers rewarding sensitivity. Figure 6: The brain's reward system Reward & addiction The reward pathway of the brain is connected to areas of the brain that control behavior and memory. It begins in the ventral tegmental area, where neurons release dopamine to make you feel pleasure. The brain begins to make connections between the activity and the pleasure, ensuring that we will repeat the behavior. Sometimes this pathway is helpful but other times, it can be devastating. For example, certain drugs can trigger the reward pathway and increase the levels of dopamine in the reward system, increasing action potentials continuous stimulation creating a prolonged sense of euphoria. Over time, an addiction can develop where repeated exposrure to dopamine surges eventually desensitizes the reward system ie: no longer to everyday normal stimuli. The only thing rewarding is the drug and by time higher doses are needed to achieve the same pleasurable effect. Page 4 of 5  Figure 7: summary of the functions of different parts of the limbic system Neurotransmitters of emotions SEROTONIN and NOREPINEPHRINE are synaptic messengers in the limbic regions of the brain involved in pleasure and motivation, suggesting that the pervasive sadness and lack of interest (no motivation) in depressed patients are related at least in part to deficiencies or decreased effectiveness of these neurotransmitters. Events perceived as being stressful can trigger depression, but the underlying link has not been determined. Figure 8: functions of Serotonin and Dopamine in regulating mood and emotions Page 5 of 5