THE LIMBIC SYSTEM

FSPhysiology Unit.,AIMST University.

Happy New Year - My Dear MBBS batch 20 Students.

Objective ?

• The objective of this lecture is to discuss the limbic cortex; differences between limbic and neocortex; reward and punishment centres in the brain and the connections of the limbic system with the hypothalamus

The Learning Outcomes :

At the end of the lecture, students should be able to:

1. Describe the limbic cortex; differences between limbic and neocortex.

2. Describe the reward and punishment centres in the brain.

3. Describe the connections of the limbic system with the hypothalamus.

4. Describe the role of limbic system and hypothalamus in the emotional behavior.

The General Organisation of the Nervous System:

The Human Brain :

The Human Brain :

Imaging of cerebral blood flow during different mental activities, shown by positron emission tomography (PET)

The nucleus accumbens (NA) has been implicated as an especially important structure of the brain reward pathway.

Other structures important in brain reward include the amygdala and the ventral tegmental area .

Brain Reward / Punishment System:

 Molecular Physiology of the Reward Pathway Dopamine Binding at the Neuron Level.

The primary neurotransmitter of the reward pathway is dopamine. 

Serotonin, Endogenous opiates, as well as GABA also modulate dopamine levels in the brain reward pathway.

Punishment circuit (the periventricular system, or PVS), which enables us to cope with unpleasant situations.

It includes various brain structures, such as the hypothalamus, the thalamus, and the central grey substance surrounding the aqueduct of Sylvius.

Some secondary centres of this circuit are found in the amygdala and the hippocampus.

Brain Punishment System:

The punishment circuit functions by means of acetylcholine, which stimulates the secretion of adrenal cortico-trophic hormone (ACTH). ACTH in turn stimulates the adrenal glands to release adrenalin to prepare the body’s organs for fight or flight.

Molecular Physiology of the Punishment Pathway

So, the Punishment centers are the following:

1. Lateral part of the posterior hypothalamus.

2. Dorsal part of the mid brain

3. Entorhinal Cortex.

Limbic systemLimbic System mainly includes:1.Limbic lobe (the cingulate gyrus & the

hippocampel gyrus.),2.Some parts of Olfactory Cortex & The

parahippocampal gyrus, 3.Hippocampus,4.Amygdala,5.Mamillary bodies (Hypothalamus) 6.Anterior nucleus of thalamus.

04/27/23 15

Limbic system

• Supports a variety of functions including:

• Emotion, • Behavior, • Long term memory, and • Olfaction

04/27/23 16

Limbic system

• The components of the limbic system located in the cerebral cortex generally have fewer layers than the classical 6-layered Neocortex, and are usually classified as Allocortex or archicortex.

• The limbic system includes many structures in the cerebral pre-cortex and sub-cortex of the brain. The term has been used in psychiatry and neurology.

04/27/23 17

• Limbic lobe–Parahippocampal gyrus: Plays a role in

the formation of spatial memory.

–Cingulate gyrus: Autonomic functions regulating heart rate, blood pressure and cognitive and attentional processing

04/27/23 18

• Hippocampus and associated structures:–Hippocampus: Required for the

formation of long-term memories and implicated in maintenance of cognitive maps for navigation.

04/27/23 19

Hippocampe ( Sea Horse), similar structure in the Limbic System called Hippocampus; Required for the formation of long-term memories

• Amygdala: Involved in signaling the cortex of motivationally significant stimuli such as those related to reward and fear in addition to social functions such as mating.

04/27/23 21

• Fornix: carries signals from the hippocampus to the mammillary bodies and septal nuclei.

• Mammillary body: Important for the formation of memory;

• Dentate gyrus: thought to contribute to new memories and to regulate happiness.

04/27/23 24

04/27/23 25

THE LIMBIC SYSTEM:

Characteristics of Limbic System

• Sparse connections between limbic system and neocortex.

• Neocortical activity can modify emotional behavior.

• Emotions cannot be turned off and on by will. There is prolonged after discharge following stimulation.

Functions• “Emotional brain”

Emotional and motivational aspects of behavior.

Provides emotional component to learning process:

Especially the amygdala.

• Associated with memoryEspecially the hippocampus.

• Associated with pain/pleasure, rage

Amygdala• Large nuclei in temporal lobe.• Afferents:

Olfactory tractSolitary nucleusParabrachial nucleusLimbic neocortex:

Cingulate gyrusParahippocampal gyrus

Amygdala Connections

Cerebral cortexOlfactory system

ThalamusBrainstem reticular formation

Hypothalamus

AMYGDALA

Striaterminalis

Ventral Amygdalofugalfibers

Regions of the Amygdala

• Large basolateral region:Provides direct input to basal ganglia and

motor system.• Small corticomedial group of nuclei:

Related to olfactory cortex.• Medial and central nuclei:

Connected to hypothalamus.

Amygdala Inputs

AMYGDALA

Corticomedial NuclearGroup

Basolateral NuclearGroup

Central Nucleus

OlfactorySystem

Temporal Lobe(associated with visual,auditory, tactile senses)

Brainstem (viscerosensory relayNuclei: solitary nucleus

and parbrachial nucleus)

VentralAmygdalofugal

Fibers

Amygdala Outputs

AMYGDALA

Corticomedial NuclearGroup

Basolateral NuclearGroup

Central Nucleus

VentralAmygdalofugal

Fibers

Septal NucleiHypothalamus

Dorsal Medial Thalamic NucleusNucleus Accumbens

Hypothalamus

Nuclei ofANS

VentralAmygdalofugal

Fibers

Stria Terminalis

Amygdala and Anger

• Electrical stimulation of the amygdala in animals and humans can elicit anger.

• Seizures involving the amygdala have been associated with violence,

• Amygdalectomy has been done for behavioral control through psychosurgery

• The effects of bilateral amygdaloid lesions generally are calming, a remarkable docility that may last months

Functions of the Amygdala• Relate environmental stimuli to coordinated behavioral

autonomic and endocrine responses seen in species-preservation.

• Responses include:Feeding and drinkingAggressive behaviorMating and maternal careResponses to physical or emotional stresses.

Hippocampus• Any sensory stimulus will go to the hippocampus ,and from

there to the Thalamus, hypothalamus and other limbic structures through FORNIX.

• Stimulation of hippocampus can cause pleasure, rage, sex drive etc.

• Important feature of hippocampus is that it creates prolonged response

• It has only three layered cortex.• It has role in learning and memory

Afferent and efferent connections of Hippocampus

• Prefrontal cortex --cingulate gyrus– septal nuclei– hippocampus—anterior nucleus of thalamus– mammillary region of hypothalamus.

• Main function: Learning and memory of complex cognitive information (new information between object and environment).

Applied Physiology - Hippocampus

• Memory loss:Damage to hippocampus portion:

Cells undergoing calcium-induced changes associated with memory

KLUVER - BUCY SYNDROMEBilateral temporal lobectomy – by Kluver & Bucy in 1937.

Features: 1.Docility 2.Hypersexuality 3.Hyperphagia 4.Manipulation & oral exploration 5.Visual agnosia.(Visual agnosia is an

impairment in recognition of visually presented objects.)

Summery:

Summery con……:

Thank u