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Function of limbic system and the cerebral cortex Prof. Romana Šlamberová, MD PhD Department of Normal, Pathological and Clinical Physiology Limbic system from Latin limbus, means "border" or "belt„ Main parts: Hippocampus Amygdala anterior thalamic nuclei limbic cortex Function: Emotion Behavior Long-term memory Olfaction History in 1878 - French physician Paul Broca first called this part of the brain „le grand lobe limbique“ in 1937 - American physician James Papez described his anatomical model of emotion, the Papez circuit. in 1952 - American physician Paul D. MacLean expanded these ideas to include additional structures in a more dispersed "limbic system" Limbic system - basic parts Amygdala - emotions (reward, fear, social functions) Hippocampus – cognition (long-term memories, map navigation, spatial memory) Parahippocampal gyrus – cognition (spatial memory) Cingulate gyrus - autonomic functions (heart rate, blood pressure) and cognition (attentional processing) Fornix - carries signals from the hippocampus to the mammillary bodies and septal nuclei Hypothalamus - autonomic functions (hormones, blood pressure, heart rate, hunger, thirst, sexual arousal, sleep/wake cycle) Thalamus - The "relay station" to the cerebral cortex Limbic system – additional parts Mammillary body - cognition (formation of memory) Pituitary gland – regulating homeostasis (hormones) Dentate gyrus – cognition (new memories) and emotions (happiness) Entorhinal cortex and piriform cortex - sensation (smell input in the olfactory system) Olfactory bulb - sensation (olfactory sensory input) Nucleus accumbens - reward, pleasure, and addiction Orbitofrontal cortex - decision making Papez circuit the major pathways of the limbic system involved in the cortical control of emotion plays a role in storing memory Papez discovered the circuit after injecting rabies virus into a cat's hippocampus and monitoring its progression through the brain. Amygdala (1) from Greek = Almond primary role in the processing and memory of emotional reactions related to many psychological disorders (social phobia, autism, bipolar disorder) Nuclei: basolateral complex (lateral, basal, accessory basal nuclei) centromedial nucleus cortical nucleus Amygdala (2) Connections to: hypothalamus - important activation of the sympathetic nervous system thalamic reticular nucleus - increased reflexes nuclei of the trigeminal nerve and facial nerve - facial expressions of fear ventral tegmental area, locus coeruleus, and laterodorsal tegmental nucleus - activation of DA, NE and E Inputs from: from the olfactory bulb and olfactory cortex to the cortical nucleus - sense of smell and pheromone-processing. from the sensory systems to the lateral amygdalae Emotions Emotions can be differentiated: Feelings are best understood as a subjective representation of emotions Moods are diffuse affective states that generally last for much longer durations than feelings and are also usually less intense than feelings Affect is an encompassing term, used to describe the topics of emotion, feelings, and moods together A distinction can be made between emotional episodes and emotional dispositions. Emotions can be measured by multidimensional scaling. The emotional experiences are divided into two dimensions known as: valences (how negative or positive the experience was) arousal (extent of reaction to stimuli) Bipolar disorder Bipolar affective disorder, manic-depressive disorder, or manic depression) is a mental illness typically classified as a mood disorder Characterized by episodes of an elevated or agitated mood known as mania, usually alternating with episodes of depression About 3% of people, a proportion consistent for both men and women and across racial and ethnic groups Causes - both genetic and environmental risk factors are believed to play a role Treatment: Psychotherapy Medication lithium, effective in treating acute manic episodes, preventing relapses, reduces the risk of suicide anticonvulsants (carbamazepin, sodium valproate, lamotrigine) Antipsychotic medications – only for short-term treatment of bipolar manic episodes Benzodiazepines may be used in addition to other medications until mood stabilizing become effective Emotions and memory Emotion can have a powerful impact on memory. The most vivid autobiographical memories tend to be of emotional events. The activity of emotionally enhanced memory retention can be linked to human evolution. The process of learning became genetically embedded in humans and all animal species in what is known as flight or fight instinct. Emotionally arousing stimuli can lead to retrograde amnesia for preceding events and anterograde amnesia for subsequent events. Hippocampus From Greek - hippos = horse, kampos = sea monster) part of the telencephalon (forebrain) located inside the medial temporal lobe of the cerebral cortex The strongest connections of the hippocampus are with the entorhinal cortex (EC). History In 1564 - the anatomist Giulio Cesare Aranzi - first used the term hippocampus (connected with the sense of smell) Around 1900 - the Russian neurophysiologist Vladimir Bekhterev - the role of the hippocampus in memory the 1950s - HM (patient) (Henry Gustav Molaison (1926– 2008) - memory-impaired patient In 1953 – William Scoville (surgeon at Hartford Hospital) removed twothirds of his hippocampus, parahippocampal gyrus, and amygdala (for diagnosed focal epilepsy in medial temporal lobes) After the surgery - severe anterograde amnesia (he could not commit new events to long-term memory). His ability to form long-term procedural memories was intact - he could learn new motor skills, despite not being able to remember learning them. Function storing and processing spatial information (London's taxi drivers – larger hippocampus) important role in the formation of new memories about experienced events (episodic or autobiographical memory) Damage to the hippocampus profound difficulties in forming new memories (anterograde amnesia) also affects access to memories prior to the damage (retrograde amnesia) Damage to the hippocampus does not affect the ability to learn new skills (playing a musical instrument) LTP – Long-term potentiation long-lasting improvement in communication between two neurons that results from stimulating them simultaneously one of the major cellular mechanisms that underlies learning and memory LTP was first observed by Terje Lømo in 1966 in the Oslo, Norway who studied the hippocampus of rabits for short-term memory. electrical stimulation to a fiber of the perforant pathway caused an excitatory postsynaptic potential (EPSP) in a cell of the dentate gyrus Basic hippocampal circuit The alveus - most superficial layer - contains axons from pyramidal neurons Stratum oriens - cell bodies of inhibitory basket cells Stratum pyramidale - cell bodies of the pyramidal neurons Stratum lucidum - mossy fibers from DG granule cells Stratum lacunosum Schaffer collateral fibers and perforant path Stratum moleculare – synaps between perforant path fibers and dendrites of pyramidal cells The hippocampal sulcus or fissure - cell-free region that separates CA1 from DG Parahippocampal gyrus a grey matter cortical region of the brain that surrounds the hippocampus important role in memory encoding and retrieval The anterior part of the gyrus includes the perirhinal and entorhinal cortices. Memory disorders Amnesia - loss of memory Hyperthymesia - condition of possessing an extremely detailed autobiographical memory reason is not known Alzheimer's disease - the most common form of dementia caused by brain damage, disease, or psychological trauma two main types of amnesia: retrograde amnesia and anterograde amnesia Cause – genetic in 1-5% Cholinergic hypothesis - reduced synthesis of the neurotransmitter acetylcholine Amyloid hypothesis - extracellular beta-amyloid (Aβ) deposits Tau hypothesis - tau protein abnormalities initiate the disease cascade Korsakoff's syndrome - a neurological disorder caused by a lack of thiamine (vitamin B1) in the brain Cause - chronic alcohol abuse and/or severe malnutrition Symptoms – retrograde and anterograde amnesia, confabulation, apathy The Hypothalamus (1) A division of the diencephalon It sub serves 3 major systems: AUTONOMIC NERVOUS SYSTEM ENDOCRINE SYSTEM LIMBIC SYSTEM 11 important nuclei: MEDIAL PREOPTIC NUCLEUS Regulates the release of gonadotropic hormones from the Adenohypophysis SUPRACHIASMIC NUCLEUS Receives input directly form the retina. Plays a role in regulating circadian rhythm ANTERIOR NUCLEUS Important in temperature regulation Stimulates PNS It’s destruction results in hyperthermia PARAVENTRICULAR NUCLEUS Synthesizes ADH- and thus regulates water balance Releases oxytocin Projects directly to autonomic nuclei of brain stem and all spinal cord levels The Hypothalamus (2) SUPRAOPTIC NUCLEUS DORSOMEDIAL NUCLEUS Contains neurons that produce factors that stimulate or inhibit action of hypothalamus Contains neurons that produce Dopamine MAMILLARY NUCLEUS Induces eating ARCUATE (INFUNDIBULAR) NUCLEUS Is the satiety center- this means that once it is stimulates, it inhibits the urge to eat LATERAL HYPOTHALAMIC NUCLEUS When stimulated in animals, causes savage behavior! VENTROMEDIAL NUCLEUS Synthesizes ADH- and thus regulates water balance Releases oxytocin Lesions (in Wernicke’s Encephalopathy patients) are associated with thiamine deficiency and alcoholicism POSTERIOR HYPOTHALAMIC NUCLEUS Plays a role in thermoregulation Lesion results in poikilothermia Hypothalamic nuclei Function of the hypothalamus AUTONOMIC Stimulation of the ANTERIOR HYPOTHALAMUS: excitatory effect on parasympathetic system Stimulation of POSTERIOR HYPOTHALAMUS: excitatory effect of sympathetic system THERMOREGULATION Stimulation of ANTERIOR HYPOTHALAMUS: regulates and maintains temperature Stimulation of POSTERIOR HYPOTHAMUS: produces and conserves heat WATER BALANCE Paraventricular (Supraoptic) nuclei synthesize ADH and control kidney water excretion FOOD INTAKE Stimulation of VENTROMEDIAL NUCLEUS inhibits the urge to eat Stimulation of LATERAL HYPOTHALAMIC NUCLEUS induces the urge to eat Cerebral cortex In humans - 2–4 mm (0.08–0.16 inches) thick neocortex (isocortex) - phylogenetically most recent part of the cerebral cortex (older part = hippocampus – archicortex) Layers from outside (pial surface) to inside (white matter): molecular layer I - apical dendrites, horizontally-oriented axons, glial cells external granular layer II - small pyramidal neurons and stellate neurons external pyramidal layer III - small and medium-size pyramidal neurons, non-pyramidal neurons with vertically-oriented intracortical axons (main cortico-cortico efferents) internal granular layer IV - stellate and pyramidal neurons (main thalamo-cortical afferents) internal pyramidal layer V - large pyramidal neurons (Betz cells in the primary motor cortex) multiform layer VI - small spindle-like pyramidal and multiform neurons (efferents to thalamus) Sensory areas Primary sensory areas - receive sensory inputs from the thalamus In general, the two hemispheres receive information from the contralateral side of the body. Topographic maps - the organization of sensory maps in the cortex correspond with the sensing organs the primary visual cortex - retinotopic map the primary auditory cortex - tonotopic map the primary somatosensory cortex - somatotopic map (homunculus) Visual cortex Located and around the calcarine fissure in the occipital lobe. Anatomically - Brodmann area BA 17 6 layers - Layer 4, which receives most visual input from the lateral geniculate nucleus Primary visual cortex – V1 (visual orientations, spatial frequencies and colors) Extrastriate visual cortical areas – V2, V3, V4, V5 – BA 18, 19 (attention, working memory, and reward expectation) Function: The dorsal stream ("Where Pathway" or “How Pathway“) - motion, object locations, control of the eyes and arms The ventral stream (“What Pathway“) - The dorsal stream (green) and ventral form recognition and object stream (purple) are shown. They representation, storage of long-term originate from primary visual cortex. memory. Auditory cortex Anatomically – BA 41, 42 Inputs from the medial geniculate nucleus of the thalamus. Function: Primary auditory cortex - in the superior temporal lobe sensation of basic characteristics of sound (pitch and rhythm) Additional areas - in the frontal and parietal lobes processing of acoustic signals (distinguished between speech, music, noise) Association auditory cortex Broca's area (pars opercularis and pars triangularis of the inferior frontal gyrus) BA 44, 45 Wernicke's area (where the temporal lobe meets the parietal lobe) posterior part of BA 22 responsible for speech production Broca’s (motor) aphasia – understands, but problems with fluent speaking responsible for understanding Wernicke’s (receptive, sensory) aphasia – can speak, but does not understand In the left hemisphere (in most people specialized for language skills) Somatosensory cortex The postcentral gyrus - the sense of touch Primary somatosensory cortex - BA 3, 1 and 2 Secondary somatosensory cortex – BA 5, 7 Lesions: Agraphesthesia - disorder of directional cutaneous kinesthesia (writing on skin) Astereognosia (tactile agnosia) - impaired ability to recognize or identify objects by touch alone Loss of vibration, proprioception, fine touch Hemineglect - ignoring the contralesional side of their body (no shaving, no make-up) It could also reduce nociception, thermoception and crude touch (but these are more in insular cortex and cingulate gyrus). Somatosensory homunculus Motor areas The primary motor cortex (M1) - the posterior portion of the frontal lobe. Precentral gyrus = BA 4 M1 contains large neurons known as Betz cells (pyramidal cells in layer V) - long axons to alpha motoneurons in the spinal cord. Involved in: planning actions (basal ganglia) refining movements (cerebellum) Motor homunculus Motor tracts The corticospinal tract originates from pyramidal cells in layer V of the cerebral cortex. About half of its fibres arise from the primary motor cortex. Other contributions come from: supplementary motor area premotor cortex somatosensory cortex parietal lobe cingulate gyrus Supplementary motor area BA 6 - on the medial face of the hemisphere, just in front of primary motor cortex (premotor cortex) Function: planning of motor actions bimanual control In contrast to M1 - actions that are under internal control (performance of a sequence of movements from memory) involved in retrieving the sequence of movements Frontal lobe Reaches full maturity around age 25 increased myelin in the frontal lobe white matter of young adults compared to that of teens A typical onset of schizophrenia in early adult years correlates with poorly myelinated (inefficient) connections between cells in the forebrain. The frontal lobe contains most of the dopamine-sensitive neurons in the cerebral cortex. Functions (involved in higher mental functions): to recognize future consequences resulting from current actions to choose between good and bad actions override and suppress unacceptable social responses determine similarities and differences between things or events Psychosurgery In the early 20th century - Portuguese neurologist Egas Moniz developed a medical treatment for mental illness Damage of the pathways connecting the frontal lobe and the limbic system Frontal lobotomy successfully reduced distress, but suppressed emotions, volition and personality. Damage of the frontal lobes Impaired mental flexibility and spontaneity, but IQ is not reduced. Talking may increase or decrease dramatically. Increase of risk taking behavior. Socialization can diminish or increase. Orbital frontal lobe damage can result in perverse sexual habits. Diminished creativity and problem solving skills. Frequent distractions. Prefrontal cortex the anterior part of the frontal lobes defined by the presence of an internal granular layer IV (in contrast to the agranular premotor cortex) Parts: orbitofrontal (OFC) and ventromedial areas (vm-PFC) dorsolateral prefrontal cortex (dl-PFC) anterior and ventral cingulate cortex ventrolateral cortex (vl-PFC) medial prefrontal cortex (m-PFC) anterior prefrontal cortex (a-PFC). Function: planning complex cognitive behaviors personality expression decision making moderating correct social behavior Prefrontal cortex