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By the end of the lecture, the student should be able to :  Describe main functions of the thalamus  Name and identify different nuclei of thalamus.  Describe the connections and functions of thalamic nuclei.  Describe the effects of lesions of the thalamus.  Describe main functions of the limbic system.  Name and identify different parts of the limbic system.  Describe the effects of lesions of the limbic system. Objectives

Thalamus  Part of diencephalon (thalamus, hypothalamus, subthalamus & epithalamus) is the largest nuclear mass of the whole body  Formed of 2 oval masses of grey matter & is the largest nuclear mass of the body  Together with the hypothalamus, it forms the lateral wall of the 3 rd ventricle.

4  It is the gateway to the cortex and relays received information to the cerebral cortex from diverse brain regions.  Axons from every sensory system (except olfaction) synapse in the thalamus as the last relay site before the information reaches the cerebral cortex. cerebellar nuclei, basal  There are some thalamic nuclei that receive input from cerebellar nuclei, basal ganglia and limbic-related brain regions. Thalamus

Thalamus has 4 surfaces & 2 ends. Surfaces  Lateral :  Medial : frequently connected to the thalamus of the opposite side by the interthalamic adhesion (massa intermedia)  Superior :  Infer ior: Ends Anterior: Forms a projection called anterior tubercle which lies just behind the interventricular foramen. Posterior: Forms a projection called Pulvinar which lies above the superior colliculus and the lateral & medial Geniculate bodies. L M S I * * interventricular foramen.

6 Relations LV IC C Thalamus 3 rd V F H ST  Lateral : Posterior limb of the internal capsule (IC)  Medial : Together with hypothalamus, forms the lateral wall of the 3 rd ventricle  Superior : Caudate nucleus (C) fornix (F) & lateral ventricle (LV)  Infer ior: Hypothalamus (H), anteromedially & Subthalamus (ST) posterolaterally.

Internal Structure  2 sheaths of white matter pass through the thalamic mass and divide it into nuclei:  External medullary lamina: lies laterally, separating the reticular nucleus from the rest of nuclei. It consists of thalamocortical & corticothalamic fibers.  Internal medullary lamina: Y- shaped bundle of myelinated fibers (afferent & efferent), dividing the thalamus into anterior, medial & lateral nuclear groups. Each group is subdivided into a number of named nuclei. 7 Extrnal Medullary lamina

8  Dorsal tier, which contains:  lateral dorsal (LD)  lateral posterior nuclei (LP)  pulvinar.  Ventral tier, which contains  ventral anterior (VA)  ventral lateral (VL)  ventral posterior (VP) nuclei  medial & lateral geniculate bodies. Lateral group is divided into:

Functional Organization of Thalamic Nuclei  All thalamic nuclei project to the ipsilateral cerebral cortex EXCEPT reticular nucleus.  Precise Point to Point projections sometimes exist between individual thalamic nuclei and restricted cortical zones. This type of nuclei are called ‘ Specific nuclei’  All specific nuclei lie within the ventral tire of the lateral nuclear group. 9

Classification of thalamic nuclei according to their projection A) Simple sensory relay nuclei: receive sensory impulses, and relay them to the sensory cortex. 1. Ventral posterolateral nucleus (VPL). 2. Ventral posteromedial nucleus (VPM). 3. Lateral geniculate body (LGB). 4. Medial geniculate body (MGB). 10  They could be classified into 3 groups, each group contains 4 nuclei: Simple sensory relay nuclei Circuit relay nuclei Associative nuclei

11 C) Associative nuclei: receive impulses from other thalamic nuclei, associate these impulses & then send processed information to the association areas of the cerebral cortex. They include: 1.Part of dorsomedial nucleus. 2.Pulvinar. 3.Lateral dorsal nucleus. 4.Lateral posterior nucleus B) Circuit relay nuclei : receive impulses from different areas of CNS and relay them to specific areas in cerebral cortex. They include: 1. Lateral ventral nucleus (project to primary motor cortex). 2. Anterior ventral nucleus ( project to premotor cortex). 3. Anterior nucleus ( project to cingulate gyrus) 4. Part of dorsomedial nucleus.

Functional Organization of the Thalamic nuclei NucleusFunctionInputsOutputs AnteriorAssociationHippocampus &mammillary body Cingulate cortex Medial nuclear groupAssociationAmygdala, Olfactory cortex & hippocampus Prefrontal cortex, hippocampus Lateral dorsalAssociationAmygdala, Olfactory cortex & hippocampus Cingulate cortex and other limbic regions Lateral posteriorAssociationSuperior colliculus, pretectumOccipital parietal, temporal association Medial geniculateSpecific nucleusInferior colliculus1ry auditory cortex Lateral geniculateSpecific nucleusLeft and right eyes1ry visual cortex VentroposteromedialSpecific nucleusTrigeminothalamic tract1ry somatosensory VentroposterolateralMed. & spinal Lemnisci1ry somatosensory Posterior nucleusSup. & Inf. Colliculi1ry somatosensory Ventral lateralSpecific nucleusGlobus pallidus1ry motor cortex Ventral anteriorSpecific nucleusGlobus pallidus1ry motor cortex IntralaminarDiffuse nucleusSpinal cord, spinothalamic, reticular formation, cerebellar nuclei, globus pallidus, sup. Colliculus. Cerebral cortex & stratum ReticularDiffuse nucleusReticular formation, corticothalamic, thalamocortical Dorsal thalamic nuclei 12

Latin  The term "limbic" is from the Latin word Limbus, for "border" or "edge".  The limbic system is a set of evolutionarily primitive brain structures located on top of the brainstem and buried under the cortex  It separates the medial surface of the cerebral cortex from diencephalon  It consists of a number of cortical & subcortical structures with complex and often looped connections that all project to the hypothalamus.

15 1. Limbic lobe. 2. Hippocampal formation. 3. Septal area. 4. Prefrontal area. 5. Amygdala 6. Anterior thalamic nuclei 7. Hypothalamus (mammillary body) 8. Fornix 9. Olfactory system. 10. Habenular nuclei The limbic system includes:

It control a variety of functions including:  Emotions, emotional responses  Behaviour & mood (happy, cry, laugh, sad, fear, anger, aggression, depression)  Motivation.  Memory.  Visceral & Motor responses involved in (sex, pleasure, hunger, and reproduction).  Olfaction. FUNCTION OF THE LIMBIC SYSTEM

Limbic lobe  C-shaped ring of grey matter on the medial side of each cerebral hemisphere, surrounding the corpus callosum.  It includes: 1. Subcallosal area 2. Cingulate gyrus 3. Isthmus 4. Parahippocampal gyrus and the 5. Uncus

 It is a seahorse shaped paired structure, one in each hemisphere.  Located in the inferomedial part of the temporal lobe.  Involved in formation, organization, storage and retrieval of memory Hippocampus

 Its principal efferent projection is to the mammillary body via a C-shaped bundle of fibers called the Fornix.  Fornix consists of: 1. Fimbria 2. Crus 3. Body 4. Column  The Fornix is an important component of PAPEZ CIRCUIT

 1937: Papez was the first to describe a relationship between limbic system components.  Papez’s circuit connects the parahippocampal gyrus, hippocampus, fornix, mamillary body, anterior thalamic nucelus and cingulate gyrus. 20 Since the initial description, connections to additional subcortical structures have been identified. Papez circuit

 The hippocampal formation is a compound structure in the medial temporal lobe of the brain  It consists of:  Hippocampus  Dentate gyrus : Which lies between hippocampus & Parahippocampal gyrus.  Subiculum (at the base of the hippocampus)  Entorhinal area (area 28)  Induseum gresium (grey matter on the upper surface of the corpus callosum). Hippocampal formation. Dentate gyrus Indusium grsium

Amygdala  Almond shaped mass of nuclei, lies near the temporal pole, close to the tail of the caudte nucleus. Connections:  Input: from association areas of visual, auditory & somatosensory cortices.  Output : to hypothalamus & brainstem autonomic nuclei, to control the autonomic centers. Function: It is involved in emotional responses, fear, anger, hormonal secretions, and memory. Lesion: results in lack of emotional responses & docility.

Site: Located anterior to the interventricular foramen Main connections: 1. To hypothalamus through medial forebrain bundle. 2. To habenular nuclei through stria medullaris thalami. Function : It provides critical interconnections and it is the pleasure zone. Septal nuclei

 Korsakoff’s psychosis (retrograde & anterogdrade amnesia)  Temporal lobe epilepsy  The hippocampus is a common focus site in epilepsy, and can be damaged through chronic seizures.  It is sometimes damaged in diseases such as herpes encephalitis,  Alzheimer’s disease : The hippocampus is one of the first brain areas to show damage in Alzheimer's disease  Schizophrenia. Limbic lobe disorders