Limbic system: peripheral and intermediate mechanism of emotions.

Limbic system: peripheral and intermediate mechanism of emotions.

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  LIMBIC SYSTEM: PERIPHERAL AND INTERMEDIATE MECHANISMOF EMOTIONS Sumitted by, Sandra sukumaran
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  Limbic system • Theterm limbic means border. The term "limbic system" originally referred to the border structures around the basal cerebrum but now encompasses the entire neuronal circuitry for emotional behavior and motivational drives. • It is located in the brain's medial temporal lobe and includes structures such as the hippocampus, amygdala, and cingulate gyrus. It extends into the diencephalon and other regions, playing a key role in emotion, memory, and motivation. • Major functions of limbic system involves: Emotional Regulation - The limbic system processes and regulates emotions like fear, pleasure, and anger. It influences how we experience and react to emotional stimuli. Memory Formation - Structures like the hippocampus are crucial for encoding and retrieving memories. The limbic system helps integrate emotional experiences with memory. Motivation and Reward - The limbic system is involved in the brain’s reward circuitry, influencing motivation, pleasure, and reinforcement learning. Behavioral Responses - It modulates behavioral responses to emotional and environmental stimuli, affecting actions related to survival, social interactions, and overall well-being.
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  • An importantroute of comminication between the limbic system and the brain stem is the medial forebrain bundle, which extends from the septal and orbitofrontal regions of the cerebral cortex downward through the middle of the hypothalamus to the brain stem reticular formation. This bundle carres fibers in both directions, forming a trunk line communication system. • A second route is through short pathways among the reticular formation of the brain stem, thalamus, hypothalamus and most other contiguous areas of the basal brain. • The limbic system is composed of several interconnected structures that play key roles in emotion, memory, and behavior. Here are the main parts of the limbic system: Hypothalamus • The hypothalamus is a small but crucial structure in the brain located in the diencephalon, situated just below the thalamus and above the brainstem. It is relatively small, about the size of an almond, and is shaped like a small, rounded mass of gray matter.
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  The hypothalamus playsa crucial role vegetative functioning and emotions include: • Emotional Regulation - The hypothalamus helps regulate emotional responses, such as fear, anger, and aggression, by interacting with the amygdala and other limbic structures. • Motivation and Drive - It helps modulate motivation, appetite, and thirst by integrating sensory information and emotional state. • Memory and Learning - The hypothalamus interacts with the hippocampus to facilitate memory formation and spatial navigation. • Reward and Pleasure - The hypothalamus is involved in processing rewarding stimuli and pleasure, associating with the ventral tegmental area and nucleus accumbens. • Social Behavior - It influences social behavior, attachment, and bonding by interacting with the oxytocin and vasopressin systems. • Hormonal Regulation - The hypothalamus controls the release of hormones that impact emotional states, such as oxytocin, vasopressin, and cortisol.
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  • Body Temperature- The hypothalamus helps regulate body temperature, which can be influenced by emotional states like stress or excitement. • Sleep and Arousal - It helps modulate sleep-wake cycles and arousal levels, impacting emotional processing and regulation. Lesions in hypothalamus leads to: • Altered hunger and satiety signals, leading to changes in appetite and body weight • Sleep disturbances (insomnia or hypersomnia) • Emotional changes, such as: Aggression, Apathy, Anxiety, Depression • Memory and cognitive impairments • Changes in sexual behavior and reproductive functions Reward and punishment functions of limbic system An animal is caged , which contains a lever at the side arranged in a manner that depressing it makes electrical contact with stimulator. Electrodes are placed at different areas of the brain so that the animal can stimulate areas of the brain by pressing the lever. If stimulating the particular area gives the animal a sense of reward then the animal presses lever again and again. Furthermore when offered the choice of eating some delectable food they opposed to eat and often chooses the electrical
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  At the sametime when electrodes are placed at some other particular areas of the brain, the animal immediately learns to off the stimulus. Stimulation of such areas causes animal to show displeasure, fear, terror, pain, and sickness. Thus punishment centers was spotted. Reward centers: 1. Ventral Tegmental Area (VTA): releases dopamine, a neurotransmitter associated with pleasure, reward, and motivation. 2. Nucleus Accumbens (NAcc): receives dopamine from VTA, involved in processing rewarding stimuli, motivation, and pleasure. 3. Hippocampus: plays a role in associating rewards with memories and learning. Punishment Centers: 1. Amygdala: processes fear, anxiety, and aversive stimuli, associated with punishment and negative emotions. 2. Hypothalamus: regulates emotional responses, including fear and anxiety, and is involved in punishment processing.
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  Key neurotransmitters: Dopamine:reward, pleasure, motivation; Serotonin: mood regulation, punishment processing; Glutamate: excitatory neurotransmitter involved in reward and punishment processing; GABA: inhibitory neurotransmitter involved in reward and punishment processing. Rage: • Strong stimulation of punishment centers of the brain causes the animal to develop a defense postures such as extending its claws lifting its tail, hissing Pitting growling and develop piloerection wide-opening of eyes and dilated pupils. • Furthermore slighter provocation causes an immediate savage attack. This pattern of behavior is called rage. • When reward centers are stimulated exactly opposite emotions of rage is shown such as placidity and tameness.
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  Amygdala The amygdala isa small, almond-shaped structure in the temporal lobe of the brain that plays a crucial role in processing emotions, particularly fear and anxiety. Its main functions include: 1. Emotional processing: The amygdala helps interpret emotional stimuli, such as facial expressions, sounds, and smells, and associates them with fear or danger. 2. Fear response: The amygdala triggers the body's "fight or flight" response, releasing stress hormones like adrenaline and cortisol, preparing the body to react to threats. 3. Memory formation: The amygdala helps store memories of emotional events, especially traumatic ones, making it easier to recall and respond to similar situations in the future. 4. Emotional regulation: The amygdala interacts with other brain regions to regulate emotional responses, preventing excessive or inappropriate emotional reactions. 5. Social behavior: The amygdala is involved in social cognition, helping us recognize and interpret social cues, like facial expressions and body language. Damage to the amygdala can lead to impaired emotional processing, reduced fear response, and altered social behavior. Understanding the amygdala's functions can provide insights into emotional regulation, anxiety disorders, and PTSD.
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  Hippocampus • The hippocampusis a structure in the temporal lobe of the brain. • It plays a crucial role in consolidating new memories, especially emotional and autobiographical ones (memory formation), Regulating emotional responses, particularly fear and anxiety (emotional processing), Providing context to memories, allowing us to recall the setting and emotions associated with an event. Helping distinguish between similar memories, preventing confusion or overlap, Generating new neurons, which is linked to improved mood and reduced stress (neurogenesis). • The hippocampus regulates emotions by interacting with the amygdala to modulate fear responses, facilitating the formation of emotional memories, influencing the prefrontal cortex's decision-making processes, regulating the release of stress hormones like cortisol, enabling the recall of emotional experiences, allowing us to learn from them. • Damage to the hippocampus can lead to: Impaired memory formation, Enhanced emotional reactivity, Increased anxiety and stress, Decreased ability to contextualize emotions.
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  Thalamus • The thalamus,a structure in the diencephalon, plays a crucial role in regulating emotions by transmitting sensory data from the environment to the cortex, influencing emotional responses, regulating the flow of information between the amygdala and cortex, impacting emotional intensity, combining sensory, cognitive, and emotional data to create a unified emotional experience, influencing the motor systems responsible for emotional displays, like facial expressions and body language, communicating with the amygdala, hippocampus, and prefrontal cortex to fine-tune emotional processing. • The thalamus regulates emotions by filtering out irrelevant sensory information, preventing emotional overload, amplifying or dampening emotional signals, depending on the context, facilitating the synchronization of neural activity across different brain regions, promoting emotional cohesion. • Damage to the thalamus can lead to: Emotional dysregulation, Altered emotional reactivity, Impaired sensory processing, Disrupted sleep and arousal patterns, Increased risk of psychiatric conditions like schizophrenia and bipolar disorder. • The thalamus acts as a critical relay station, influencing the flow of emotional information
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  Cingulate gyrus • Thecingulate gyrus is a structure in the medial part of the brain that plays a key role in various higher-level cognitive and emotional processes, including: Identifying mistakes and discrepancies between expected and actual outcomes. Modulating emotional responses, particularly in relation to empathy, guilt, and anxiety. Facilitating understanding of others' perspectives and emotions. Contributing to the consolidation of memories, especially emotional ones. Regulating attentional resources and motivation towards goals. Processing and integrating pain information. • The cingulate gyrus is divided into sub-regions, each with distinct functions: Anterior cingulate cortex (ACC): Involved in error detection, conflict monitoring, and emotion regulation. Posterior cingulate cortex (PCC): Engaged in memory retrieval, attention, and default mode processing. Mid-cingulate cortex (MCC): Participates in motor control, error detection, and motivation. • Damage to the cingulate gyrus can lead to: Emotional dysregulation, Impaired empathy and social cognition, Memory deficits, Attentional difficulties, Altered pain perception, Psychiatric conditions like depression, anxiety disorders, and schizophrenia.
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  Basal ganglia The basalganglia are a group of structures in the brain that play a crucial role in movement control, habit formation, and emotion regulation. Functions of the basal ganglia includes: • Motor control: Facilitates smooth, coordinated movements by regulating the flow of information from the cortex to the thalamus. • Habit formation: Involved in the formation and execution of habitual behaviors, such as routines and skills. • Emotion regulation: Contributes to emotional processing, particularly in relation to motivation, pleasure, and reward. • Cognitive processing: Participates in attention, working memory, and executive functions. • Reward-based learning: Plays a role in learning from rewards and punishments. Damage to the basal ganglia can lead to: Movement disorders (e.g., Parkinson's disease, Huntington's disease), Habit formation deficits, Emotional dysregulation, Cognitive impairments, Addiction and impulsivity. The basal ganglia act as a critical interface between the cortex and thalamus, regulating the flow of information and facilitating adaptive behaviors. Dysfunction in the basal ganglia has been implicated
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  Reference Guyton and Hall:medical physiology: pg:731-738