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StraightforwardLogic5266

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Cardiff University

2024

Cardiff University

Sean Wyatt

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neuroanatomy thalamus neuroscience biology

Summary

This lecture notes covers the thalamus, focusing on its structure and function in the brain. Diagrams help illustrate the relationships between different nuclei and how the thalamus acts as an essential relay for sensory information to the cortex and other brain regions.

Full Transcript

BI2432: Fundamental Neuroscience Thalamus Dr Sean Wyatt (wyattsl@cf.ac.uk) Coronal section Horizontal section Where is the...

BI2432: Fundamental Neuroscience Thalamus Dr Sean Wyatt (wyattsl@cf.ac.uk) Coronal section Horizontal section Where is the caudate thalamus? internal nucleus capsule thalamus caudate posterior lentiform nucleus thalamus anterior nucleus Lies in the diencephalon of the forebrain 3rd ventricle The diencephalon also internal incorporates capsule - Epithalamus pons lentiform cerebellum nucleus - Subthalamus - Metathalamus Mid-sagittal section - Hypothalamus thalamic adhesion thalamus The thalamus can be thought of as the “gatekeeper” for the cortex and modulator of its midbrain function 4th ventricle pons The thalamus is made up of many individual nuclei Internal medullary Anterior group ANT = anterior nucleus lamina Medial group DM = dorsomedial LD = lateral dorsal Transverse Dorsal tier LP = lateral posterior section PUL = pulvinar TRN Lateral group VA = ventral anterior Ventral tier VL = ventral lateral Internal medullary lamina VPL = ventral posterior lateral VPM = ventral posterior medial LGN = lateral geniculate dorsal nucleus MGN = medial geniculate nucleus Intralaminar CM = centromedian PF = parafascicular (not shown) ventral LGN MGN Reticular TRN = thalamic reticular nucleus Thalamic nuclei have discrete roles in regulating the access of information to the cortex Thalamic nuclei can be categorized as: - Relay nuclei - Association nuclei - “other” nuclei Relay nuclei (motor, sensory and limbic relay nuclei) receive information from the periphery and forward it to the cortex Association nuclei connect different areas of the cortex with each other (pulvinar and dorsomedial nucleus) “Other” nuclei include: intralaminar nuclei - interact with projecting pathways of the brainstem and the basal ganglia (drive and consciousness) reticular nucleus – master regulator of information flow to the cortex - synchronizes the activity of the thalamus with cortical activity allowing a conscious appreciation of stimuli and events All thalamic nuclei have bidirectional communication with the cortex > 75% of thalamic neurons are projection neurons and the rest are inhibitory interneurons Inputs to thalamic nuclei Example: sensory inputs to cortex Inputs to thalamic nuclei can be divided into two categories Specific inputs (drivers) contain information that needs to be Regulatory forwarded to the cortex Cortex input Regulatory inputs (modulators) modulate the driver inputs Modulation and and determine whether it is sent to the cortex prioritizing of information to be Regulatory inputs arise from: Output sent to the cortex to - cortex cortex TRN regulatory input - thalamic reticular nucleus (TRN) Control of - projection systems of the brainstem selective Thalamus attention Regulatory input (cholinergic, dopaminergic, Projection systems of the serotonergic and noradrenergic) brainstem Examples of selective attention Blocking of much sensory input to the cortex during sleep Driver input Specific Filtering out extraneous noise when listening to a conversation Sensory information in a noisy environment intended for the information cortex Ignoring distracting visual and auditory stimuli when concentrating on reading a book or playing an instrument Functions of the Thalamus Control of sensory information entering primary sensory cortex (except olfaction) Control of selective attention - descending input from the cortex commands what information needs to reach the cortex and this is executed by the thalamus – avoids information overload and confusion Emotional and subjective response to sensation - achieved via connections with the limbic system and prefrontal cortex - e.g. sensations agreeable, not agreeable, effects on mood etc. (limbic system has links to the dopaminergic brainstem reward system) Awareness of nociceptive input (from tissue damage) as pain - nociceptive input from tissue damage is not perceived as “pain” until it reaches the thalamus and is relayed to the cortex – the perception of pain due to tissue damage can be delayed in extreme situations to promote survival Motor integration through links with the basal ganglia, cerebellum and motor cortex - the thalamus forms an essential component of the extrapyramidal motor system Aspects of memory - e.g. the thalamus has links to the hippocampus and factual-declarative and geographic memory is relayed to the cortex via the thalamus Control of cortical arousal and consciousness by linking the brainstem Ascending Reticular Activating System to the cortex Special senses and the thalamus Primary auditory Cochlea Cochlear nuclei Inferior colliculus MGN and auditory association cortices thalamus Primary visual and Retina Optic tract LGN visual association cortices Inferior colliculus MGN = Medial geniculate nucleus LGN = Lateral geniculate nucleus Connections between the medial geniculate nucleus (MGN) and the auditory cortices are reciprocal Connections between the lateral geniculate nucleus (LGN) and the visual cortices are reciprocal Optic tract MGN This allows the flow of auditory and visual LGN information to the cortex to be controlled by the cortex and other thalamic nuclei (e.g. the thalamic reticular nucleus (TRN)) Control of selective attention Somatosensation and the thalamus Trigeminothalamic tract VPM =ventral posteromedial nucleus (a.k.a. trigeminal lemniscus) VPM thalamus Somatosensory cortex Spinothalamic tract and Dorsal column – medial lemniscus VPL VPL =ventral posterolateral nucleus The trigeminothalamic tract carries information on simple and complex touch, temperature, itch, nociception and conscious proprioception to the VPM The spinothalamic tract carries information Face VPL representation on simple touch, temperature, itch and VPM nociception to the VPL The dorsal column-medial lemiscus pathway Spinothalamic tract Dorsal column – carries information on complex touch and medial lemniscus conscious proprioception to the VPL Trigeminothalamic tract Connections between the VPM and cortex and the VPL and cortex are reciprocal Thalamus roles in motor integration Caudate The caudate nucleus, putamen and globus nucleus pallidus are part of the basal ganglia system Basal ganglia, cerebellum and thalamus are VA components of the extrapyramidal motor system Motor thalamus cortex The ventral anterior (VA) and ventral lateral (VL) VL nuclei of the thalamus are motor relay nuclei The caudate and putamen (striatum) receive input from primary and association motor cortices Putamen Driver input to the VA is from the globus pallidus cerebellum Globus Driver input to the VL is from the cerebellum pallidus Motor input is integrated in the thalamus with thalamic inputs from other sources The VA and VL nuclei relay information to the primary and association motor cortices The VA and VL nuclei provide feedback to the caudate nucleus, putamen and cerebellum VPM... and receive feedback from motor cortices Limbic relay thalamic nuclei (anterior, lateral dorsal and dorsomedial nuclei) Limbic System - a system of cortical and other forebrain structures involved in the control of emotional and drive-related responses (e.g. fear, rage, defence) functional outcome Consolidation of memories Mammillary bodies Anterior nucleus Cingulate cortex + Selective attention Cingulate cortex functional outcome Motivation Entorhinal cortex Lateral dorsal nucleus + Selective attention Parietal cortex Cingulate cortex functional Inhibition of inappropriate Diffuse input from outcome behaviour + Dorsomedial nucleus Prefrontal cortex limbic system Mediates executive function Orbitofrontal cortex ANT DM Anterior nucleus – main driver input from mammillary bodies Lateral dorsal nucleus – main driver input from entorhinal cortex Dorsomedial nucleus – diffuse driver input from limbic system Thalamic association nuclei (pulvinar and dorsomedial nuclei) Thalamic association nuclei regulate interactions between one part of the cortex and another Association nuclei receive inputs from a number of subcortical structures:- - basal ganglia - brainstem reticular formation association nuclei integrate information from subcortical structures with inputs from association cortices to modulate the - other brainstem nuclei interactions of different cortical areas with each other - parts of the limbic system Direct corticocortical connections Transthalamic Frontal Frontal connections Parietal Association Thalamic association Parietal Association between cortices nuclei cortices Occipital Occipital association “gating” function Temporal Temporal cortices Subcortical structures Dorsomedial (DM) thalamic nucleus The DM thalamic nucleus has input from the prefrontal cortex Gating of information to prefrontal cortex It also has inputs from basal ganglia, entorhinal cortex and parts of the limbic system (e.g. amygdala and hippocampus) Executive control Outputs from the DM nucleus are mainly to the prefrontal cortex with some output to the basal ganglia, cingulate cortex (limbic Prefrontal Association Basal system) entorhinal cortex and association cortices cortex cortices ganglia The DM nucleus through its output to the prefrontal cortex has a role in executive control including planning of goal Limbic circuit directed behaviour - includes suppressing other behaviours Motivational and that would conflict with those ongoing DM emotional aspects of motor behaviour The DM nucleus through its multiple reciprocal connections has a role in memory encoding – particularly declarative Entorhinal Limbic memory but also emotional memory cortex system Through its reciprocal connections with the entorhinal cortex the DM nucleus has a role in olfactory learning, odour memory and odour discrimination Olfactory learning Reciprocal connections of the DM nucleus with the limbic and odour memory + system and basal ganglia regulate motivational and odour discrimination emotional aspects of motor behaviour The pulvinar nucleus and higher-order visual processing The pulvinar nucleus makes extensive reciprocal connections with parietal, temporal, frontal and occipital association areas of the cortex It is functionally connected to the DM nucleus and has Visual association cortex similar connections to the limbic system and prefrontal cortex as the DM Pulvinar Visual salience The pulvinar nucleus also receives input from the visual VPM nucleus Attention to a specific visual stimulus association cortex (and retina) Visuospatial working memory The pulvinar nucleus integrates visual information with Frontal information from other cortical association areas Parietal Association Occipital cortices allows an evaluation of which particular visual stimuli Temporal are most important (visual salience) directs attention to specific visual stimuli The pulvinar nucleus plays an important role in visuospatial working memory The pulvinar nucleus and higher-order auditory processing The pulvinar nucleus also plays an important role in auditory processing and language auditory association cortex The pulvinar nucleus has reciprocal connections with the auditory association cortex In particular, the pulvinar nucleus has reciprocal Pulvinar Understanding auditory information connections with the superior temporal gyrus which is VPM nucleus Auditory short-term memory important for the understanding of language and for Language tasks auditory short-term memory Frontal The pulvinar nucleus integrates auditory information with information from other cortical association areas Parietal Association Occipital cortices Temporal facilitates the understanding of auditory information and enhances auditory short-term memory The pulvinar nucleus engages and coordinates cortical areas that are important for auditory tasks Intralaminar thalamic nuclei (centromedian (CM) and parafascicular (PF) nuclei) Consciousness and drive The CM/PF complex receives cholinergic input from the brainstem reticular system (ascending reticular activating system) The CM/PF complex also receives dopaminergic input from Centromedian nucleus ventral tegmental area (VTA) of the midbrain Diffuse, nonspecific VTA is part of the dopaminergic “reward system” providing cortical areas drive to prioritize essential behaviours like eating, drinking and reproduction Striatum Arousal, (caudate and awareness Output from the CM/PF complex is to diffuse cortical areas putamen) and vigilance and influences the overall function and arousal state of the cortex (level of awareness and vigilance) Prioritizing and selecting CM/PF cortical inputs to the The CM/PF complex also projects to the striatum basal ganglia helps prioritize cortical inputs to the striatum Cholinergic input Dopaminergic input from brainstem from brainstem (VTA) Important for facilitating goal-orientated behaviours The Thalamic reticular nucleus (TRN) The TRN is a sheet of neurons that surrounds the thalamus TRN Example: sensory processing All cortex – thalamus reciprocal projections give rise to a collateral branch which innervates the TRN The TRN in turn projects back to the thalamus to the exact area from where the afferent input to the TRN originated + Cortex All TRN neurons are GABAergic and inhibitory and can modulate excitatory input from thalamic nuclei to the cortex Sensory information + + The TRN regulates the flow of information from the relayed to the cortex - Thalamic reticular Thalamus nucleus (TRN) thalamus to the cortex and is an important component of + regulating selective attention The TRN has been proposed to be the primary Driver input sensory determinant of consciousness because it ultimately controls access of all thalamic nuclei to the cortex Learning outcomes After assimilating the content of this lecture, you should: Have an appreciation that the thalamus is more than a mere “relay station” and that it is comprised of many nuclei that work together to tightly regulate the flow of information to the cortex and thereby modulate cortical function and behavioural outcomes Be able to outline the principal functional roles of the thalamus as a whole and identify some of the specific functions of each thalamic nucleus

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