Thalamus facts
[[Home]] -> [[BiologicalLifeResearch]] -> [[BiologicalHierarchyFull]] -> [[bioThalamus]] ---- * this page is about dorsal thalamus (DTH=TH/D) * other parts of thalalus are: ** ventral thalamus (TH/V) = RN, SVG, ZI ** epithalamus = habenula, pineal gland '''see also''': * [http://en.wikipedia.org/wiki/Thalamus Wikipedia] == Overview == * thalamus sorts sensory input, helps sort REALITY from FICTION == Structure == http://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Constudthal.gif/637px-Constudthal.gif * [http://www.scholarpedia.org/article/Thalamus Scholarpedia] http://www.scholarpedia.org/w/images/8/80/ThalamusFigure4.gif '''inputs''' * 90%-95% of synaptic inputs onto the relay cells, arise from: ** local GABAergic neurons ** reticular cells ** interneurons ** feedback projection from layer 6 of cortex ** ascending projection from various scattered cell groups in the brainstem reticular formation * relayed inputs ** sensory inputs * modulatory inputs ** from cerebral cortex ** limbic pathways make input ** cerebellar and basal ganglia inputs ** from reticular thalamic nucleus ** from various brain stem areas '''functions:''' * site where sensory inputs can be modulated * relay for cerebellar and basal ganglia inputs to the cerebral cortex ** these are feedback pathways, since the cerebellum and basal ganglia respond to outputs from the cerebral cortex '''paths''' * thalamus nucleus -> cortex -> thalamus nucleus (the same) ** filtering thalamic inputs to the cerebral cortex http://www.twow.net/ObjText/BrainDgms/MamBSubAsr.gif http://www.scholarpedia.org/w/images/thumb/e/e9/ThalamusFigure5_new.gif/400px-ThalamusFigure5_new.gif '''contents''' * many inhibitory interneurons * many neuromodulatory neurotransmitter systems (such as 5HT and NE systems) have terminations within thalamic nuclei * the relay cell to interneuron ratio is between 3 and 4 to one == Divisions == * anterior nucleus (AN) - '''association''' - connections similar to the LD nucleus * lateral subnuclei ** reticular thalamic nucleus - '''nonspecific''' - brain stem reticular formation, cerebral cortex, thalamus -> inhibitory input to thalamic nuclei (arousal and alertness) ** ventral tiers subnuclei (total 15 nuclei, project to neocortex) *** ventral posterior nuclei (VP) **** ventral posteromedial nuclei (VPM) - '''ff/relay''' - trigeminothalamic -> cortex **** ventral posterolateral nuclei (VPL) - '''ff/relay''' - medial lemniscal and spinothalamic connections -> cortex *** ventral lateral nuclei (VL) - '''fb/relay''' - cerebellum/dentate nucleus, basal ganglia -> primary motor, premotor cortex (motor feedback from the cerebellum and basal ganglia to the cerebral cortex) *** ventral anterior nuclei (VA) - '''fb/relay''' - basal ganglia (medial globus pallidus, substantia nigra, parts reticulata) -> premotor cortex, supplementary motor area ** dorsal tiers subnuclei *** pulvinar (PV) - '''association''' - superior colliculus, association cortex -> secondary visual areas, association areas in parietotemporal region (visual perception and eye movements, probably relating to attention) *** lateral posterior nuclei (LP) - '''association''' - like pulvinar *** lateral dorsal nuclei (LD) - '''association''' - hippocampus -> mamillary bodies -> LD -> posterior cingulate cortex (emotional learning) * medial subnuclei ** medial dorsal nucleus (MD) *** medial subdivision - '''association''' - solitary nucleus, substantia nigra reticulata, amygdala and ventral pallidum -> insular cortex, orbital frontal cortex and subcallosal region (autonomic regulation and emotions) *** lateral subdivision - '''association''' - superior colliculus, olfactory cortex and the ventral pallidum -> frontal eye fields, anterior cingulate cortex (controlling eye movements, attending to visual stimuli, emotional tone) ** midline nuclei - '''nonspecific''' ** intralaminar nuclei *** central median - '''fb/relay''' - (reciprocal connections with the globus pallidus and with the premotor cortex) *** parafascicular nuclei - '''nonspecific''' * metathalamus (near pulvinar) ** MGB - medial geniculate body (auditory relay nucleus) - '''ff/relay''' - tonotopically auditory afferents from inferior colliculus -> primary auditory cortex ** LGB - lateral geniculate body (principal visual relay) - '''ff/relay''' - retinotopic input -> primary visual cortex == Projection == * each thalamic projection neuron can exist in one of two basic physiological states: ** "tonic mode" *** neurons respond like other neurons to depolarization and hyperpolarization ** "burst mode" *** oscillatory mode" *** neurons in this state have an intrinsic rythmicity *** during sleep, most thalamic neurons are in burst mode *** neurons cannot communicate specific information *** if a novel stimulus is presented, the sudden change from burst to tonic mode may be a major factor in alerting the cortex == Functional View == '''Sensory Relay:''' * sensor/retina -> '''DTH/V/LGB''' -> PCA/V1 (1-order visual relay) * sensor/inferior colliculus -> '''DTH/V/MGB''' -> PCA/A1,2 (1-order auditory relay) * BSA/medial lemniscus, ALS, TTT, STT -> '''DTH/V/VP''' -> {PCA/S1,2,3 (1-order somatic relay); HCA/insula (1-order taste relay); ACA/M/4 (?)} * {BSA/anterior olfactory nucleus; SCA (pain)} -> '''DTH/M/MD''' -> {HCA/insula (1-order olfactory relay); ACA/PFC (1-order pain relay)} * {SCA; BSA/olfactory} -> '''DTH/I/sheet''' -> (diffuse) * BSA/SN,SC,PAG,CR -> '''DTH/V/VM''' -> ACA,PCA/layer1 (attention) '''Motor relay:''' * {BSA/CR; BGA/GP,SN} -> '''DTH/V/VL,VA''' -> ACA/M,PM,SM * BGA/GP,SN -> '''DTH/I/CM''' -> ACA/M '''Association:''' * (many) -> '''DTH/L/PV''' -> {PCA/occipital,parietal; HCA/temporal} * limbic/mammillary -> '''DTH/A/AV,AM,AD''' -> ACA/CG * limbic -> DTH/L/LD -> ACA/CG == Axons terminated in Thalamus == * 2 types - R (round) and E (extended), excitatory, using GLU * R-type terminals are characteristically large (3 nm in diameter), although variable in size and actual shape. They conform to the classical type-2 endings, as described in specific thalamic nuclei. The associated axonal terminations are concentrated in sharply delimited, round arbors and '''carry of the order of 100 terminals''', that typically '''end on proximal dendrites''' * E-type axons have stalked or spinous terminations of classic type-1 corticothalamic endings. Their axonal terminal fields are elongated and quite extended (1-3 mm) and '''carry between 500 and 1,000 E terminals''' that typically '''end on distal dendrites''' * in the LGN (and in pulvinar), the driving input from the retina is provided by R-type axon terminals, with type-2 synapses; the input back from cortical area V1 has E-type axon terminals, with type-1 synapses - modulating input, (though there are many more E-type than R-type axons) * cortical E-type axons derive from medium to small pyramidal cells in the lower cortical layers. They are located in layer 6, and as a rule always have collaterals in the thalamic reticular nucleus * cortical R-type axons originate from pyramidal cells in cortical layer 5 == Axons terminated in Cortex == * projections from thalamus to cortex also fall into two classes * first type goes mainly into layer 4 or lower layer 3, with a minority also contacting processes in layer 6 ** projection cells in magno- and parvocellular laminae of LGN are prominent examples of such a connection that can very reliably drive cortical cells, despite their small number of synapses. ** 2.8% of all excitatory synapses on a layer 4C spiny stellate cell originate from magnocellular cells in LGN * other type projects to layer 1, but not exclusively - modulating connection ** examples - cells in the interlaminar zones of the LGN that project into the superficial layers of V1 * rules ** (1) If a cortical area projects to a thalamic region from cortical layer 6, then if there is a reverse projection, it goes mainly into layer 4 or lower layer 3 ** (2) if a cortical area projects to a thalamic region from cortical layer 5, then if there is a reverse projection it avoids layer 4 and often goes mainly to cortical layer 1. These thalamocortical projections are usually much more diffuse than the layer 4 projection.