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    LIMBIC SYSTEM

    - SAMANTHA CARNEIRO

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    The limbic system consists of the limbic

    lobe and other subcortical structures andtheir connections. Although not

    empirically proven, the limbic system is

    a functional concept which may be

    employed to explain various brain

    functions.

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    COMPONENTS OF THE LIMBIC SYSTEMCOMPONENTS OF THE LIMBIC SYSTEM

    The brain regions that constitute the limbic system are:

    Limbic cortex

    Cingulate gyrus

    Parahippocampal gyrus

    Hippocampal formation

    The dentate gyrusHippocampus

    Subicular Complex

    Amygdala

    Septal areaHypothalamus

    These structures form a complex network for

    controlling emotion.

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    Circuits ofCircuits of amygdalaamygdalaAmygdala serves to integrate information

    processing between prefrontal / temporal

    association cortices and the hypothalamus.

    The amygdala has two major output pathways:

    Dorsal route and Ventral routeBasolateral circuit

    This circuit encodes information about social

    signals and social plans for social acts. The circuithas been proposed as a substrate for the human

    ability to infer the intentions of others from their

    language, gaze and gestures

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    Amygdala Connections

    Cerebral cortex

    Thalamus

    Brainstem reticular formation

    Hypothalamus

    AMYGDALA

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    Limbic System and Basal NucleiLimbic System and Basal Nuclei

    Temporal lobe

    Hippocampus

    Amygdala

    Ventral Striatum

    Caudate Nucleus

    Anterior Cingulate Gyrus

    Globus Pallidus

    Substantia nigra

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    FUNCTIONSOFTHE LIMBIC SYSTEM

    Olfaction

    The limbic structures are closely related to theolfactory cortex and have a role in the processing

    of olfactory sensation. Amygdala is involved in

    the emotional response to smell

    Appetite and eating behaviours:

    Amygdala plays a role in food choice. The lateral

    nucleus of the hypothalamus is the centre for

    control of feeding whereas the ventromedial

    nucleus functions as the satiety centre

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    Sleep and dreams:

    The limbic system is one of the most active brain

    areas during the process of dreaming. Thesuprachiasmatic nucleus of hypothalamus is the

    circadian rhythm generator

    Emotional responsesFear:

    Fear responses are produced by the stimulation of

    the hypothalamus and amygdala. Amygdalardestruction abolishes fear and its autonomic and

    endocrine responses. Amygdala is also involved in

    fear learning

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    Autonomic and endocrine responses to

    emotion: Limbic stimulation causes changes in

    respiration and blood pressure. The stimulation ofthe cingulate gyrus and hypothalamus can elicit

    autonomic responses. The massive sympathetic

    discharge during stress is called the flight or frightresponse.

    SexualSexual behaviorbehavior::

    The medial preoptic area of the hypothalamus is

    a key structure in the central control of male

    sexual behavior.

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    Addiction and motivationAddiction and motivation

    The reward circuitry underlying addictive behavio

    includes amygdala and nucleus. This pathway isinvolved in the motivation to take drugs of abuse

    and the compulsive nature of drug-taking

    MemoryMemory

    Emotional memory: Emotion has powerful

    influence on learning and memory. Amygdala, in

    conjunction with prefrontal cortex and medial

    temporal lobe, is involved in consolidation and

    retrieval of emotional memories. Hippocampus is

    critical for long-term memory storage.

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    Diencephalic memory system:The diencephalic

    memory circuit consists of the hypothalamus,

    mammillary body and the dorsomedial nucleus of

    thalamus. This circuit is important for the storage

    of recent memory

    Social cognition:Social cognition:

    Social cognition refers to thought processes

    involved in understanding and dealing with otherpeople. Limbic structures involved are the

    cingulate gyrus and amygdala.

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    CLINICAL IMPLICATIONSEpilepsy

    Temporal lobe epilepsy most often caused by

    hippocampal sclerosis.

    Limbic encephalitisLimbic encephalitis is a paraneoplastic syndrome

    that has been reported with carcinoma of the lung,

    breast and some other primaries. Afflicted patientsdevelop subacute onset of memory loss, dementia,

    involuntary movements and ataxia.

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    DementiaDementia

    Degenerative changes in the limbic system have a

    role in neurodegenerative diseases, particularlyAlzheimer's

    Anxiety disordersAnxiety disordersAnxiety disorders may be the result of a failure of

    the anterior cingulate and hippocampus to

    modulate the activity of the amygdala

    SchizophreniaSchizophrenia

    There is reduced limbic volumes in schizophrenia.

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    Affective disordersAffective disorders

    The dysfunction of this system especially the

    anterior limbic network is suggested in bipolardisorder

    AutismAutismAutism and Asperger's syndrome involve the

    disproportionate impairment in specific aspects of

    social cognition.L

    imbic structures involvedinclude the cingulate gyrus and amygdala

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    ADHDADHD

    Limbic structures have been implicated in the

    genesis of ADHD. Enlarged hippocampus andDisrupted connections between the amygdala and

    orbitofrontal cortex is seen in children and

    adolescents with ADHD

    Korsakoff's psychosisKorsakoff's psychosis

    Korsakoff's psychosis is caused by damage to

    mammillary bodies, dorsomedial nucleus of

    thalamus and hypothalamus. It is a syndrome

    associated with chronic prominent impairment of

    recent and remote memory

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