LIMBIC SYSTEM Judith Molnr Department of Anatomy Histology

LIMBIC SYSTEM Judith Molnár Department of Anatomy, Histology and Embryology, 2018

Cerebral cortex • Isocortex – 6 layers (neocortex) • Allocortex – 3 -4 layers (limbic cortex) – Archicortex • Hippocampus, dentate gyrus – Paleocortex • Olfactory bulb, tuberculum olfactorium and the piriform cortex (amygdala, uncus, gyrus parahippocampalis ant. ) – Periallocortex (transitional regions)

archipallum paleopallium neopallium striatum

Development of telencephalon

arcipallium paleopallum neopallium striatum

• The brain stem and basal ganglia are the parts of the brain what is called reptilian brain, and this is the most ancient part of the brain. Supervise the balance, territority, sexual behaviour, feeding, and other vital functions. • The midlle part is the limbic system, what inludes the septum, amygdala, hypothalamus, hippocampal complex, and the cingulate gyrus, is the mammalian brain, which direct emotions, memory and social behaviour. • The primate brain is the cerebral cortex. The human brain is the latest „product” of evolution, what makes possible the higher functions, like language, planning, abstraction etc.

Primates brain Inelligence Racionality Mammalian brain Memory Emocional Reptile brain Survival Instinctual

Limbic system • Broca: 1878, limbic lobe – Cingulate gyrus, parahppocampal gyrus • Papez: 1937 – Hippocampal formation – emotions • Mac. Lean: 1949 – Limbic system – racional behaviour

The limbic system • The functions of the limbic system: storing, recalling memories, establishing the emotional state, linking the conscious, intellectual functions of the cortex with the unconscious and vegetative functions of the brainstem. • Cooperation between sensory, motor and association cortical areas makes it possible to perform tasks. The operation of the limbic system influences the will to perform the tasks

Structures of the limbic system • • • Olfactory bulb Hippocampus, dentate gyrus Hypothalamus Amygdala Nucleus anterior thalami Corpus mamillare Septum pellucidum Commissura habenularum Cingulate gyrus Parahippocampal gyrus Entorhinal cortex Limbic brain stem structures

Structures of the limbic system

Schematic illustration of the location of the limbic system between the diencephalon and the neocortical hemispheres

Schematic illustration of the concentric main components of the limbic system.

Connections of the limbic system • Fornix – hippocampus-corpus mamillare – Fasciculus mamllothalamicus – Fasciculus mamillotegmentalis • Stria terminalis – amygdala-hypothalamus • Stria medullaris thalami – septum-habenula • Striae longitudinales • Cingulum – hippocampus-prefrontalis cortex • Fasciculus retroflexus • Medial forebrain bandle

• Hippocampus • Amygdala

Hippocampal formation • Dentate gyrus • Hippocampus • Subiculum

Formation of the hyppocampal complex

Histological structure of hippocampus • Layers – Stratum moleculare • Entorhinalis cortex afferents (perforant branches) • Mossy fibers from dentate nucleus • Schaffer collaterals (CA 1 – CA 3) – Stratum pyramidale – Stratum oriens • Basket cells

Pyramidal cells of hippocampus • The dendrites are parallel to one another resulting in summation of extracellular current flow and hyperexcitability seen in epilepsy. • The pyramidal dendrites are perpendicular to the cortical surface resulting in different layers of cortex impinging at different points along the dendritic tree. • The pyramidal dendrites contain dendritic spines that amplify currents (inputs) so that distant synaptic sites can more easily generate action potentials. • The pyramidal cells (dendrites) receive inputs from basket cells that regulate excitability of the pyramidal cells through recurrent inhibition.

Efferents of the entorhinal cortex • From the entorhinal cortex to hippocampus – two pathways – Perforants branches – dentate gyrus – Alvear branches – hippocampus

Fornix • • Alveus Fimbria hippocampi Crus fornicis Commissura fornicis Fornix Columna fornicis Corpus mamillare

Fornix • Precommissural fornix: septal nuclei, ventral striatum and cingulate gyrus • Commissural fornix: contralateral hippocampus • Postcommissural fornix: columna fornicis, corpus mamillare, mamillothalamic tract, anterior thalamic nucleus

Connections of the hippocampus

Afferents of the hippocampus • Entorhinal cortex – Neocortex – Temporal lobe – Orbital cortex – Cingulate gyrus – Olfactory bulb • Fornix – Septal areas, hypothalamus • Amygdala • Contralateral hippocampus

Hippocampus • The memories are not stored in the hippocampusban but the cognitive and sensory experiences are organized in long-term memory, stored in different brain regions. • Learning • Consolidation of memory • Long term memory

Hippocampus • Hippocampus mediates many cognitive functions – reciprocal connections with cortex • Allocentric and spatial learning and memory – cognitive map • Decision-making mechanisms – predicting future events helps to make decisions

Learning processes • When using spatial strategies, the hippocampus has greater activation. • In striatum, response strategies have greater activity. • There is a reverse ratio of gray matter activity in striatum and hippocampus.

Amygdala • Afferents – Lateral olfactory stria – Ventral amygdalofugal patways – Stria terminalis – Temporal lobe • Efferents – Ventral amygdalofugal pathways – Stria terminalis – Hippocampus – Entorhinal cortex – Dorsomedial thalamic nucleus

The pathways of the amygdala • • • Ventralis amygdalofugal pathway – Nucleus accumbens septi – Globus pallidus, ventral striatum – Nucleus olfactorius anterior – Gyrus cinguli anterior part – Septum – Hypothalamus Stria terminalis – Septalis area – Hypothalamus – Habenula – Contralateral amygdala Direct connections – Hippocampus – Entorhinal cortex – Thalamus, dorsomedial nucleus – Brain stem

Amygdala • Amygdala is an integration center: emotions, mediation between emotion-directed behavior and motivation. • It organizes appropriate emotional reactions triggered by information received from sensory organs. • Amygdala's efferentes to hypothalamus – visceral and somatic motor responses and prefrontal cortex – conscious emotional decisions.

Gyrus cinguli • The gyrus cinguli plays a role in expressing emotions – gestures

• Proust: In search of lost time • H. M. – Bilateral medial temporal lobectomy to surgically resect the anterior two thirds of hippocampus, parahippocampal cortices, entorhinal cortices, piriform cortices, and amygdalae. Severe side effect was that he became unable to form new memories. • Korsakoff psychosis – B 1 vitamin deficiency – anterograde amnesia, amnesia of fixation, confabulation, – apathy – the patients lose interest in things quickly • Taxi drivers – London • Newborn mitotic activity in hippocampus • Nobel prize: John O’Keefe, May-Britt Moser and Edvard I. Moser – for their discoveries of cells that constitute a positioning system in the brain – Hippocampus and entorhinal cortex

References • Barr, M. L. , Kiernan, J. A. The Human Nervous System. An Anatomical Viewpoint. Philadelphia, 1993. • Burt, A. M. , Textbook of Neuroanatomy. 1993. W. B. Saunders Company • Hajdu, F. , Vezérfonal a Neuroanatómiához. Semmelweis Orvostudományi Egyetem, 1996. • Kahle, W. , Leonhardt, H. , Platzer, W. Color Atlas/Text of Human Anatomy, Vol. 3. Nervous System and Sensory Organs. Stuttgart, New York, 1993. • Komoly, S. , Palkovits, M. , Gyakorlati Neurológia és Neuroanatómia. 2018. Medicina • Szentágothai J, Réthelyi M: Functional Anatomy, Medicina, 2019 • https: //nba. uth. tmc. edu/neuroscience/toc. htm • https: //www. mcb 80 x. org/lessons