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The Limbic System. The Limbic System. The Limbic System. In 1878, Paul Broca defined the limbic (Latin limbus :border ) lobe as the cerebral convolutions that surround the brain stem and central commissures consisting primarily of the parahippocampal and cingulate gyri .
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The Limbic System • In 1878, Paul Broca defined the limbic (Latin limbus:border) lobe as the cerebral convolutions that surround the brain stem and central commissures consisting primarily of the parahippocampal and cingulategyri. • In 1937, Papez suggested the limbic lobe was part of a larger integrated system involved in emotional behavior that is now referred to as the limbic system. • Different authors have defined its components in various ways, but the main structures include the cingulategyrus, the parahippocampalgyrus, the hippocampal formation, the hypothalamus, the septal nucleus, the amygdala, the mammillary bodies, several thalamic nuclei, the basal forebrain, olfactory structures, and the subcallosal region as well the tracts connecting them.
The Limbic System • First it includes several regions of one form of cortex called the limbic cortex; this cortex is also known as the cingulate cortex as shown in the picture. • Besides the limbic cortex, the most important parts of the limbic system are the hippocampus and the amygdala. The fornix and mammilary bodies are also parts of the limbic system. • The limbic system has been implicated in learning and memory and emotions. The implication in emotions involves feelings and expressions of emotions, emotional memories and recognition of emotions in other people.
The Limbic System • The limbic system (or paleomammalian brain) is a complex set of brain structures that lies on both sides of the thalamus, right under the cerebrum. • It is not a separate system, but a collection of structures from the cerebrum, diencephalon, and midbrain, including the: • Hippocampus • Amygdalae • Anterior thalamic nuclei • Septum, • Limbic cortex • Fornix
The Limbic System • It supports a variety of functions, including: • Emotion • Behavior • Motivation • Long-term memory • Olfaction. • It appears to be primarily responsible for our emotional life, and has a great deal to do with the formation of memories.
The Limbic System • Anatomy • The limbic system is the set of brain structures that forms the inner border of the cortex. • 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 cerebralpre-cortex and sub-cortex of the brain. The term has been used within psychiatry and neurology, although its exact role and definition have been revised considerably since the term was introduced. • The following structures are, or have been considered to be, part of the limbic system:
The Limbic System • Hippocampus: • Required for the formation of long-term memories and implicated in maintenance of cognitive maps for navigation. • The hippocampus consists of two “horns” that curve back from the amygdalae. • It appears to be very important in converting things that are “on one's mind” at the moment (in short-term memory) into things that one will remember for the long run (long-term memory). • If the hippocampus is damaged, a person cannot build new memories and lives instead in a strange world where everything he or she experiences just fades away, even while older memories from the time before the damage are untouched.
The Limbic System • 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. • Furthermore, the anatomy of amygdalae are two almond-shaped masses of neurons on either side of the thalamus at the lower end of the hippocampus. • The amygdalae stimulate the hippocampus to remember many details surrounding the situation, as well.
The Limbic System • Fornix: • is a C shaped bundle of axon which carries signals from the hippocampus to the mammillary bodies and septal nuclei. • Mammillary body: • Locates at the ends of the anterior arches of the fornix. It is involved with the process of recognition memory. • Septal nuclei: • Located anterior to the interventricular septum, the septal nuclei provide critical interconnections. The septal area isn't related to the smell, but it is the pleasure zone in animals.
The Limbic System Mammillary Body:a small, round, paired cell group that protrudes into the interpeduncularfossa from the inferior aspect of the hypothalamus. It receives hippocampal fibers through the fornix and projects fibers to the anterior thalamic nuclei and into the brainstem tegmentum.
The Limbic System • Limbic lobe • Parahippocampalgyrus: • Plays a role in the formation of spatial memory. • Cingulategyrus: • Autonomic functions regulating heart rate, blood pressure and cognitive and attentional processing. • Dentate gyrus: • Thought to contribute to new memories.
The Limbic System • In addition, these structures are sometimes also considered to be part of the limbic system: • Entorhinal cortex: Important memory and associative components. • Piriformcortex:The function of which relates to the olfactory system. • Fornicate gyrus: Region encompassing the cingulate, hippocampus, and parahippocampalgyrus. • Nucleus accumbens: Involved in reward, pleasure, and addiction. • Orbitofrontal cortex: Required for decision making.
Fornix • Fornix: • The major efferent fiber tract arising from the hippocampal formation. • It is the direct continuation of the alveus and the fimbria. • Below the splenium of the corpus callosum, these structures become the crus of the fornix. • Under the body of the corpus callosum, the two crura fuse to become the body of the fornix which is attached to the corpus callosum superiorly by the septum pellucidum.
Fornix • Anteriorly, the body turns ventrally in front of the interventricular foramina and splits into right and left half. • These vertical portions are referred to as the columns of the fornix. The main portion of the columns (postcommissural fornix) pass inferiorly through the hypothalamus and terminate in the mammillary bodies. • A small portion of the columns (precommissural fornix) split off above the anterior commissure and terminate anteriorly in the septal nuclei.
Hippocampus and Fornix Uncus:a prominent bulge on the medial surface of the temporal lobe. The bulge contains the medial portion of two structures: anteriorly the amygdala and posteriorly the peshippocampi. These structure are separated by the most anterior portion of the temporal horn of the lateral ventricle which is lies horizontally in a coronal plane. The uncus is part of the parahippocampalgyrus.
The Papez Circuit • The Papez circuit is a neural pathway in the brain first described by American neuroanatomistJames Papezin 1937. • Papez believed that the circuit was involved with emotions. • Since the circuit's discovery, many experiments have been conducted to explore the system and how its structures work together. • Recent studies show that it has a more significant role in memory functions than in emotions. • The Papez circuit was later modified by American neuroscientist and physician Paul D. MacLean and now, the circuit is known as the limbic system. • Damage to parts of the Papez circuit have shed light on not only its function, but on possible diagnosis of many disorders relating to memory.
The Papez Circuit • The Papez circuit involves various structures of the brain. • It begins and ends with the hippocampus (or the hippocampal formation). Fiber dissection indicates that the average size of the circuit is 350 milimeters. The Papez circuit goes through the following neural pathway: • hippocampal formation (subiculum) → fornix → mammillary bodies → mammillothalamic tract → anterior thalamic nucleus → cingulum → entorhinal cortex → hippocampal formation. • A photograph of the inferior medial view of the brain when dissected clearly shows the layout of the Papez circuit. Due to the location of the structures in the circuit, the resulting shape is a limbus.
The Papez Circuit • This is what drove MacLean to call the circuit the limbic system when he later modified the circuit. • Various studies indicate that the Papez circuit is greatly influenced by the cerebellum and that perhaps the hippocampus is not the starting point of the circuit. • Anatomically, this would make sense since the cerebellum is connected to the circuit with many fine fibers and fiber bundles. • Chemical lesions on the cerebellum seem to have an inhibitory effect on the circuit. Animal behavioral studies show that electrical stimulation of the anterior cerebellum can cause arousal, predatory attack, and feeding responses, all of which are thought to be expressions of emotion. Overall, these studies provide evidence that the cerebellum may also be included in an emotional system of the brain.
Affective Behaviors Emotions Joy Anger Pleasure Fear
Limbic Function Functional Aspects of Limbic System 1.Emotion - Affective Behavior Amygdala Limbic and Prefrontal Cotex - Desire, Motivation, Goal-directed Behavior Hypothalamus and Brain Stem - ANS - maintenance of self (appetites) maintenance of species (sexual function) cf. Klüver-Bucy Syndrome 2. Memory and Learning Papez Circuit cf. Korsakoff’s syndrome
Limbic Function Evolution and Limbic System - Triune Concept of MacLean Protoreptilian Brain (R Complex) ---- Instinct Paleomammalian Brain --- Limbic System ---- Emotion Neomammalian Brain --- Neocortex --- Analytical, Reasoning
Introduction Concept of Limbic System Broca (1877) - ‘La Grand Lobe Limbique’ Papez (1937) - ‘Limbic Circuit’ - emotion MacLean (1952) - ‘Limbic System’ - visceral brain Nauta (1972) - ‘Septo-hypothalamo-mesencephalic continuum’
PAUL BROCA (1824-1880) JAMES PAPEZ (1883-1958)
Limbic System - term of Paul MacLean (1952) - Visceral Brain - triune concept of brain evolution Hypothalamus Nucleus accumbens amygdaloid nuclear complex orbitofrontal cortex Some psychiatric implications on physiological studies on fronto- temporal portions of limbic system (visceral brain). Electroencephalogr Clin Neurophysiol 4: 407-418, 1952 Paul D. MacLean
Main Components of Limbic System Olfactory Cortex Spinal Cord & Brain Stem NAUTA’SSepto-(Preoptico)-Hypothalamo- Mesencephalic Continuum Hippocampal Formation Septal Region Hypothalamus Limbic Midbrain Area Amygdaloid Nuclear Complex Limbic System
Expression of Emotion Septo- hypothalamo- mesencephalic continuum
Components of the Limbic System (I) Basal Forebrain Area Substantia Innominata Basal Nucleus of Meynert Ventral Pallidum Nucleus Accumbens (Septi) Septal Region Septal Area Paraterminal Gyrus Subcallosal Gyrus Septal Nuclei Dorsal, Lateral and Medial Septal Nuclei Nucleus of Diagonal Band of Broca Bed Nucleus of Stria Terminalis Amygdaloid Nuclear Complex Corticomedial Nuclear Group Basolateral Nuclear Group Central Nucleus TELENCEPHALON Limbic Lobe Gyrus Fornicatus Cingulate Gyrus Parahippocampal Gyrus Hippocampal Formation Hippocampus Dentate Gyrus Subiculum Hippocampal Rudiments Fasciolar Gyrus Indusium Griseum Olfactory Cortex (Rhinencephalon) - Piriform Lobe Prepiriform Cortex Periamygdaloid Cortex Entorhinal Cortex
Components of the Limbic System (II) DIENCEPHALON Thalamus, Limbic Anterior Nuclear Group Mediodorsal (MD) Nucleus Midline Nuclei Hypothalamus Preoptic Region Preoptic Periventricular Nucleus Medial Preoptic Nucleus Supraoptic Region Suprachiasmatic Nucleus Anterior Nucleus Supraoptic Nucleus Paraventricular Nucleus Tuberal Region Dorsomedial Nucleus Ventromedial Nucleus Infundibular (Arcuate) Nucleus Mammillary Region Lateral, Medial and Intermediate Mammillary Nucleus Posterior Nucleus Epithalamus Habenular Nucleus Medial Habenular Nucleus Lateral Habenular Nucleus Pineal Gland MESENCEPHALON Limbic Midbrain Area Median Raphe Nucleus Dorsal Raphe Nucleus Ventral Tegmental Area Dorsal Tegmental Nucleus Periaqueductal Gray
