Limbic System
LIMBIC SYSTEM
- The neuronal circuit controlling emotional behavior & drives motivations.
COMPONENTS
Described from outer to inner
- Limbic cortex/Subcortical area
- Hippocampal formation/Subcortical structure
- Hypothalamus
1. Limbic cortex/Subcortical area:
- Forms a ring around cerebral cortex
Parts:
- Cingulate gyrus
- Rim of cortical tissue around corpus callosum
- Parahippocampal gyrus
- Subcallosal gyrus
- Orbitofrontal cortex
- Uncus
2. Hippocampal formation/Subcortical structure:
- Middle Layer
- Surrounds hypothalamus
Parts:
- Septum
- Hippocampus
- Amygdala
- Para-olfactory area
- Anterior nucleus of thalamus
- Portion of basal ganglia
3. Hypothalamus
- Central element surrounded by subcortical structures
- Major part of limbic system
NEURONAL CONNECTIONS
- Limbic system is two-way link between brainstem & neocortex
Pathways:
1. Papex circuit:
- Inter-connected closed circuit formed by union of limbic system nuclei.
Components:
- Hippocampus
- Mamillary body
- Anterior thalamic nuclei
- Cingulate gyrus
2. Medial forebrain bundle:
- Major efferent connection of limbic system
- One of reward system component
Reward center:
- Ventromedial hypothalamic nuclei + medial forebrain bundle
3. Other connections:
Subiculum
- Collection of grey matter bt. hippocampus & neocortex
- Provides reciprocal connections bt limbic system & neocortex
Amygdala:
- Located in forebrain
- One each beneath two temporal lobe
- Inter-connected to other limbic system structures.
Linking unit:
- Along with hippocampus, amygdala is extensively connected with Association cortex area & Hypothalamus.
- Thus, provides link between limbic system & neocortex.
Window of limbic system:
- Has two-way connections with hypothalamus
- Receives intputs from limbic system & higher cortical association areas.
- Hence, “Window of Limbic system”
FUNCTIONS OF LIMBIC SYSTEM:
1. Development of emotions:
- Fundamental role of limbic system: Generation of emotions
Neurophysiology of emotions:
- Emotions originate in limbic system
- Limbic system adds feelings to sensory experiences
- Allows ‘Feelings’ to direct ‘Behavior’.
Components in emotional state:
- After development of emotions, emotional state has 3 components,
- Central, peripheral & co-ordinating component
Central component:
- Limbic cortex – Central component of emotions & evaluation site.
- Direct action –
- Eg., Feeling of fear
Peripheral component:
- Hypothalamus – Co-ordinates peripheral & autonomic component of emotions.
- Effects on peripheral areas –
- Eg., sweating, dryness of mouth i.e, peripheral effects related to fear.
Co-ordinating component:
- Amygdala – Pivotal role in co-ordinating pperipheral & central component
2. Autonomic responses:
- Limbic & hypothalamic projection on reticular formation
- Important role in generation autonomic responses
- Increased BP, HR & Piloerection
- Especially in emotional states
3. Feeding behavior:
- Role in act of finding food
4. Sexual behavior:
- Basic urge for sexual behavior
5. Fear, rage, & placidity:
- Fear & rage – Emotions provoked to hostile environment
Fear
- Produced by Amygdala
Rage
- Produced by stimulation of lateral hypothalamus
Placidity
- Caused by bilateral destruction of amygdala
- Remaining calm despite grave provocation
6. Punishment & reward:
Punishment center:
- Lateral portion of posterior hypothalamus &
- Dorsal region of midbrain
Reward/pleasure center:
- Medial forebrain bundle &
- Ventromedial nuclei of hypothalamus
7. Memory & Learning:
- Memory function localized to
- Hippocampus &
- Temporal limbic cortex.
ASSOCIATED CONDITIONS:
KLUVER-BUCY SYNDROME:
- Neuro-behavioural syndrome
- Associated with bilateral lesions in anterior temporal horn or amygdala
- Heinrich Kluver & Paul Bury first described syndrome in 1937
Causes:
- In humans occurs due to destruction of amygdaloid body & inferior temporal cortex
- Commonly due to Herpes Simplex Encephalitis (HES)
Features:
Visual agnosia
- Inability to recognize familiar objects
- No visual impairment
Oral tendencies
- Examination of surrounding with mouth instead of eyes
Hypermetamorphosis:
- Desire to explore everything
Emotional changes:
- Dulled emotions
- Facial movements & vocalization – less expressive
- Loss of fear – “Placidity”
Hypersexuality
- Increase in sexual behavior including masturbation, homo- & heterosexual acts
- Attempt to copulate with inanimate objects
Shared features:
- Between humans & experimental monkey features shared in common include,
- Visual agnosia
- Loss of normal fear & anger responses
- Hypersexuality – less pronounced in humans.
Exam Question
LIMBIC SYSTEM
- The neuronal circuit controlling emotional behavior & drives motivations.
COMPONENTS
- Described from outer to inner
- Limbic cortex/Subcortical area
- Hippocampal formation/Subcortical structure
- Hypothalamus
1. Limbic cortex/Subcortical area:
- Cingulate gyrus Parahippocampal gyrus
- Subcallosal gyrus
- Orbitofrontal cortex
- Uncus
2. Hippocampal formation/Subcortical structure:
- Surrounds hypothalamus
Parts:
- Septum
- Hippocampus
- Amygdala
- Para-olfactory area
- Anterior nucleus of thalamus
- Portion of basal ganglia
3. Hypothalamus
- Central element surrounded by subcortical structures
- Major part of limbic system
NEURONAL CONNECTIONS
- Has two-way link between brainstem & neocortex
Pathways:
1. Papex circuit:
- Inter-connected closed circuit formed by union of limbic system nuclei.
Components:
- Hippocampus
- Mamillary body
- Anterior thalamic nuclei
- Cingulate gyrus
2. Medial forebrain bundle:
- Major efferent connection of limbic system
- One of reward system component
Reward center:
- Ventromedial hypothalamic nuclei + medial forebrain bundle
3. Other connections:
- Subiculum
- Provides reciprocal connections bt limbic system & neocortex
Amygdala:
Linking unit:
- Along with hippocampus, amygdala is extensively connected with Association cortex area & Hypothalamus.
- Thus, provides link between limbic system & neocortex.
Window of limbic system:
- Has two-way connections with hypothalamus
- Receives inputs from limbic system & higher cortical association areas.
- Hence, “Window of Limbic system”
FUNCTIONS OF LIMBIC SYSTEM:
1. Development of emotions:
- Fundamental role of limbic system: Generation of emotions
Neurophysiology of emotions:
- Emotions originate in limbic system
- Limbic system adds feelings to sensory experiences
Components in emotional state:
Central component:
- Limbic cortex – Central component of emotions & evaluation site.
Peripheral component:
- Hypothalamus – Co-ordinates peripheral & autonomic component of emotions.
Co-ordinating component:
- Amygdala – Pivotal role in co-ordinating pperipheral & central component
2. Autonomic responses:
- Limbic & hypothalamic projection on reticular formation
3. Fear, rage, & placidity:
Fear
- Produced by Amygdala
Rage
- Produced by stimulation of lateral hypothalamus
Placidity
- Caused by bilateral destruction of amygdala
4. Punishment & reward:
Punishment center:
- Lateral portion of posterior hypothalamus &
- Dorsal region of midbrain
Reward/pleasure center:
- Medial forebrain bundle &
- Ventromedial nuclei of hypothalamus
6. Memory & Learning:
- Memory function localized to Hippocampus & Temporal limbic cortex.
ASSOCIATED CONDITIONS:
KLUVER-BUCY SYNDROME:
- Neuro-behavioural syndrome.
- Associated with bilateral lesions in anterior temporal horn or amygdala
Causes:
- In humans occurs due to destruction of amygdaloid body & inferior temporal cortex
- Commonly due to Herpes Simplex Encephalitis (HES)
Features:
- Visual agnosia.
- Emotional changes
- Loss of normal fear & anger responses – “Placidity”.
- Hypersexuality
- Less pronounced.
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