limbic system.pdf

Cingulate gyrus Thalamus Mammillary bodies Cingulum Limbic System Parahippocampal gyrus Dr. Yang V Li fornix Office: Irvine Hall 346 E-mail: [email protected] Hippocampus Hippocampus Amygdala Limbic System Major Components: Hippocampus (memory, learning) Amygdala (emotions, fear and reward) Cortical are...

Cingulate gyrus Thalamus Mammillary bodies Cingulum Limbic System Parahippocampal gyrus Dr. Yang V Li fornix Office: Irvine Hall 346 E-mail: [email protected] Hippocampus Hippocampus Amygdala Limbic System Major Components: Hippocampus (memory, learning) Amygdala (emotions, fear and reward) Cortical areas (cingulate and parahippocampal gyri) Anatomy: The limbic system includes many structures in the cortical and subcortical regions. Hippocampus Amygdala Parahippocampal gyrus Cingulate gyrus Mammillary body Anterior nucleus of the thalamus Olfactory bulb and olfactory cortex Hypothalamus Ventral striatum Nucleus accumbens Function: Emotion and Memory. Cingulate gyrus Thalamus Mammillary bodies Cingulum Limbic System Parahippocampal gyrus fornix Hippocampus Hippocampus Amygdala Cortical Loop of Limbic System Prefrontal lobe uncinate Cingulate gyrus Parahippocampal gyrus Cingulum Prefrontal lobe uncinate Cingulate gyrus Cortical loop of Limbic System Cingulum Parahippocampal gyrus Limbic System Anterior or Prefrontal Association cortex Cingulate gyrus Thalamus Cingulum Posterior or Temporal Association cortex Mammillary bodies Parahippocampal gyrus fornix Hippocampus Olfactory Amygdala To hypothalamus To ventral tegmental areas To striatum of basal ganglion Hippocampus and Memory Connections: Hippocampus articulates with other brain areas through perforant pathway and fornix. Both these pathways carry the afferent as well as the efferent projections. Perforant Pathway is the main afferents (input) to dentate gyrus to begin trisynaptic circuit (PP to DG to CA3 to CA1) Fornix is the main efferents (output), fibers arise from field CA1 and the subiculum, projects to mammillary bodies, anterior nucleus of thalamus, and to association area of neocortex. Memory and the hippocampus [H.M.] 27 year old man Suffered Bilateral temporal lobe seizure Surgery to remove hippocampal formation Dr. William Scoville (1906—1984), the neurosurgeon who operated on Case H. M. in 1953. MRI images of the brain of patient H.M. consequences of H.M.’s surgery… reduced the frequency of H.M.’s seizures.. produced a profound anterograde amnesia anterograde amnesia - can’t make new memories retrograde amnesia - can’t recall past memories [H.M.] exhibits a profound anterograde amnesia, and does not know where he lives, who cares for him, or what he ate at his last meal. There are two important aspects of H.M.’s case that we shall consider... the nature of his memory impairment the brain regions affected by his surgery the nature of H.M.’s memory impairment Anterograde amnesia Explicit (declarative) memories – memory for everyday facts and event involving conscious recollection spared Implicit (non-declarative) memory-memory for motor skills or procedures recalled without conscious awareness Explicit vs. Implicit Memories Explicit memory – medial temporal lobe – factual information – autobiographical information Implicit memory – tied to sensory and motor systems – repetition memory; recall is automatic – can be studied in simple organisms Explicit memory: can be concisely expressed in declarative statements. Semantic: a memory for facts, e.g. we use semantic memory to store and recall objective knowledge that we learn in school and from books. Episodic: a memory for events and personal experience, e.g. We use episodic memory when we recall that we saw the first flowers of spring. “Right now, I'm wondering, have I done or said anything amiss? You see, at this moment everything looks clear to me, but what happened just before? That's what worries me. It's like waking from a dream. I just don't remember.“ - HM Significance of the case. HM has not only been important for the knowledge he has provided about memory impairment and amnesia, but also because his exact brain surgery has allowed a good understanding of how particular areas of the brain may be linked to specific processes hypothesized to occur in memory formation. In this way, he has provided vital information about brain pathology, as well as having helped form theories of normal memory function. Classification: Memory Can be Grouped According to: Temporal Classification Anterograde / Retrograde Short term memory (STM), and Long term memory (LTM) Consolidation of LTM. STM --> LTM? Most information in STM is forgotten LTM is improved by many meaningful associations Increasing time in STM increases chances of STM-->LTM Information Type (Long term memory) Explicit/Declaritive Memory Episodic (events and personal experience) Semantic (a memory for facts) Implicit/Procedural/Skill Memory Information Modality (Verbal, Visual, Spatial) Working Memory Formation and Storage of Explicit memories Encoding, the processes by which newly learned information is attended to and processed when first encountered. Consolidation, the processes that alter the newly stored and still labile information to make it more stable for long-term storage. May involve expression of genes and the synthesis of new protein, structural changes, and LTP. Storage, the mechanism and sites by which memory is retained over time (unlimited memory?) Retrieval, processes that permit the recall and use of the stored information. The Importance of Experience or Association in Information Storage From Purves Neuroscience Brain Systems Underlying Long-Term Storage of Declarative Memory The cerebral cortex is the major long-term repository for many aspects of declarative memory. From Purves Neuroscience Hippocampus Removal of this organ results in an inability to transfer memory from short term to long term storage – specifically what was affected were explicit memories (those that can be stated) Studies show that hippocampal lesions alone can result in profound anterograde amnesia for declarative memory. Hippocampus & Long-term Potentiation (LTP) Neuron types: Pyramidal neurons: CA1, CA3 regions Granule neurons (dentate region) LTP is a feature of the hippocampal pathways Schaffer collateral (CA1) Mossy fiber (CA3) Perforant (Dentate) LTP is formed in all three regions From Purves Neuroscience What molecular mechanisms allow these properties to manifest themselves? Structural Changes in Synapses during the development of Memory Increase the release of neurotransmitter Increase in number of transmitter vesicles Increase in number of synapses Changes in structures of the dendritic spines Increase in number of receptors Changes in the configuration of receptors Structural Changes in Synapses during the development of Memory (Cont.) Is LTP involved in memory formation? Mice that lack the NMDA receptor in the hippocampus have a defect in LTP and spatial memory. LTP is reduced Spatial learning is effected Hippocampus: Clinical Implications Alzheimer’s Disease Epilepsy Depression and stress Schizophrenia Amygdala Amygdala Function: Emotion (emotional learning/memory, fear and reward, feeding behaviors) Facial expression or facial recognition Anatomy & connections Receiving signals from olfactory system and neocortices Anterior commissure connects the two amygdala. To hypothalamus ( via stria terminalias) To Cingulate gyrus To Mammillary body To the nuclei in the brainstem To striatum of basal ganglion To Hippocampus Learned Emotional Responses are Processed in the Amygdala Fear-Potentiated Startle Amygdala to: Parabrachial Nucleus: increased respiratory rate Lateral Hypothalamus: sympathetic discharge Cingulate Gyrus & Locus Coeruleus: NE release, increased HR, BP and fear Periaquaductal Grey: Defensive behavior, freezing, jumping and running. Amygdala: Facial expression and Facial recognition There are two anatomically separate neural systems; (1) Located in the amygdala, is concerned with the implicit memory of the appropriate cues that signal emotions expressed (by faces). (2) Located in the inferotemporal cortex (hippocampus?), is involved in the explicit memory of facial identity. Case of S.M. Amygdala: Reward Pathway Mesolimbic pathway: ventral tegmental area to Amygdala & Nucleus Accumbens Addiction Ventral tegmental Area (VTA) Reward and desire Motivation and emotional response Memory Addiction & Reward center Nucleus Accumbens Amygdala Limbic cortex can cause hallucinations and schizophrenia if not functioning properly Effects of Stimulating the Amygdala Same effects as those by direct stimulating hypothalamus Several types of involuntary movement Emotional responses (rage, or pleasure) Sexual activities Effects of Bilateral Ablation of the Amygdala —The Klüver-Bucy Syndrome (1) not afraid of anything (fearless) (2) extreme curiosity about everything (3) forgets rapidly (4) Hyperorality (5) Hypersexuality Amygdala Clinical Implications Depression and stress or emotional dysregulation Autism Alzheimer’s Disease Epilepsy Schizophrenia Parahippocampal gyrus A grey matter that surrounds the hippocampus Input to hippocampus Complex thought associations from Wernicke’s area Function: Important in memory encoding and retrieval. Clinical Implications from fMRI studies Loss of spatial memory Schizophrenia Seizure Alzheimer’s disease Cingulate gyrus Receives inputs from the anterior nucleus of the thalamus and the neocortex, as well as from somatosensory areas Projects to the parahippocampal gyrus or entorhinal cortex via the cingulum. Projects to the insular Function: emotion formation and learning, and memory Affective and emotional response to pain. Clinical Implications from Lesion: Pain Bipolar disorders and depression Schizophrenia Alcohol dependence Attention deficit hyperactivity disorder Mammillary Bodies Consist of two groups of nuclei, the medial mammillary nuclei and the lateral mammillary nuclei. Relay for impulses coming from the hippocampi (& amygdalae), via the mamillothalamic tract to the thalamus and cerebral cortex. Function: vital for memory Affection & emotion Clinical Implications: Alcohol intoxication (thiamine deficiency) Autism Amnesia Henry Gustav Molaison