Isothalamic parts or regions Isothalamus

1 isothalamic parts or regions

1.1 superior region s (including anterior nucleus)
1.2 medial region: medial nucleus
1.3 posterior region. pulvinar. pu (with lp part)
1.4 basal region b

1.4.1 geniculate region. g

1.4.1.1 medial geniculate nucleus gm
1.4.1.2 lateral geniculate nucleus gl


1.4.2 lateral region l (or v)

1.4.2.1 gustatory territory varc
1.4.2.2 tactile lemniscal territory vpc=vpl+vpm
1.4.2.3 deep lemniscal territory vpo (or vps)
1.4.2.4 cerebellar territory vim or vl
1.4.2.5 pallidal territory vo
1.4.2.6 nigral territory va

isothalamic parts or regions

the different functional modalities represented in thalamus segregated in specific anatomical regions, differentiated cerebral systems receive afferent projections. there more corticothalamic thalamocortical axons. corticothalamic endings of 2 kinds. classical projection emanates layer vi of cortex, axons thin , have long, straight, trajectory through thalamus, not respecting intrathalamic borders. emit short perpendicular collaterals (the arborization formin thin cylinder (globus , scheibel). terminal synapses glutamatergic. second kind of corticothamic axons rockland type ii (1994). emanates larger pyramidal cells , thicker. ending small, dense , globular. synapses located close soma of thalamic neuron, forming center of glomerular complexes. isothalamus serves function of transforming , distributing prethalamic information cortex.

the thalamic parts delineated lamellar , cellular limiting elements, according founding system of burdach (1822), constituted classic thalamic nuclei. these have been later further subdivided. louvain symposium (in dewulf, 1971) made recommendation call classical subdivisions region . 1 region may made of 1 or several nuclei. these may have 1 (or several) partes, if there particular coafference instance.

the region separated superior lamella anterior region (a). region separated medially medial lamina lateral region (l). separated thalamic mass geniculate bodies (g). remaining isothalamus made of medial region (m, medial medial lamina) , posteriorly, no complete separation in man, of posterior regio or pulvinar (pu). last 2 represent huge medioposterior ensemble. classical separation relay nuclei, receiving specific subcortical afferences or association nuclei, not, cannot retained absolute. lateral region , geniculate bodies indeed receive strong lower specific afferences , can seen sensorimotor part of thalamus. medioposterior ensemble, in of volume not receive subcortical afferents , abundant afferences associative cortex in some, ventral parts, in fact receives subcortical afferences, such tectal, spinothalamic or amygdalar. anterior region receives particular afference not entirely subcortical (directly or indirectly subiculum).

thalamic regions may functionally inhomogeneous. elements of lateral region have been separated ventral , dorsal (in fact named lateral) nuclei. subdivision no more hold true. cytoarchitectonics have partly failed. differentiates anatomofunctional parts major afferent systems present in thalamus terminal parts of axons , axonal arborisations. three-dimensional analyses of distribution of axonal ending coming same source show occupy own space in thalamus, called territory. such main territory no mix or overlap in primates neighbouring territories (percheron et al. 1998). made possible solid partition of thalamus. these territories may cover 1 or several nuclei. analyses of three-dimensional geometry of main afferent territories in macaques have shown dorsal element on transverse sections posterior part of preceding territory. there no dorsal nuclei . 1 reason why nomenclature selected nomina anatomica , terminologia anatomica (1998) hardly applicable. evolution of thalamus follows of cortex , there differences including between primates (new world monkeys , old world; old world , humans), means universal nomenclature valid in species not reachable.

superior region s (including anterior nucleus)

the superior region comprises 2 elements linked during long time , later wrongly separated: nucleus anterior , nucleus superficialis, or superior (previous nucleus lateralis dorsalis). nucleus anterior, divided several entities in non-human species, undivided in man. two, anterior , superficial, nuclei separated lateral , medial regions lamella superior , everywhere surrounded capsule of white matter, including lamina terminalis. second nucleus (superficialis or superior) posterior , in succession first. 2 constituted in same manner. main difference mode of afference. both receives information subiculum of hippocampus in 1 case indirectly , in other directly. efferent axons of subiculum follow fornix. @ anterior part of fornix, part of them go down mammillary body. neurons of mammillary bodies give axons forming thick , dense mamillo-thalamic tract (of vicq d azyr), ends in nucleus anterior. part of subicular axons not end in mamillary body as, @ level of foramen of monro, turn posteriorly. of them end anterior nucleus great quantity end in nucleus superficialis. selective target of efferent axons anterior nucleus anterior cingulate cortex, of superfial nucleus posterior cingulate, overlap. axons of these parts of cingulate cortex, linked through large cingulum (longitudinal bundle located @ base of cingulate cortex), return parahippocampal gyrus. circuit referred papez circuit (1937) said author substrate emotion. there have been many further other elaborations (including limbic system ). papez circuit in fact not close (at hippocampal level). in addition, second nucleus, superficial nucleus, not taken consideration, has similar connections , participates in other close or linked circuits. better known effect of lesion of mamillary bodies, of mamillothamic bundle , fornix, if bilateral, particular (anterograde) amnesia (korsakoff syndrom).

medial region: medial nucleus

the nucleus medialis corresponds part located medial lamina medialis. in anterior part of lamina, oral intralaminar cellular part makes clear border. no more true posteriorly pulvinar. due constitution , connection, 2 constitute common set corresponding largest mass of human thalamus. in non human primates, medial nucleus (often named dorsomedian) subdivided several subnuclei. admitted no longer case in humans, makes comparison old world monkeys difficult. subcortical afferences documented in macaques (amygdalar, tectal). there no arguments in favour of existence in humans. majority of afferences comes cortex, reciprocated corticothalamic efferences. in macaques, spatial distribution of connection said circunferential (goldman-rakic , porrino, 1985), medial cortical areas being linked medial parts of nucleus , lateral dorsal lateral dorsal. true in humans. strong interrelation between medial nucleus , frontal cortex known long. lobotomies intended cut connection. there other mediocortical connections; cingulate cortex, insular cortex , premotor cortex.

posterior region. pulvinar. pu (with lp part)

pulvinar means pillow in latin. constitutes posterior pole of thalamus , posterior border indeed smooth. anteriorly there incomplete boundary medial nucleus. 2 have in fact common connections both thalamocortical , corticothalamic. case instance frontal cortex. usual subdivisions not fit distribution of cortical afferent. common find description of nucleus lateralis posterior ( lp). part of pulvinar passing on lateral region , giving in transverse sections image of ventral , dorsal (or lateral) subdivision. sagittal sections show pulvinar(lp) ensemble single curved entity. whole receives in same identical afferences. main medial part receives flat islands of axonal terminations frontal, parietal, temporal , preoccipital cortex. 1 part of pulvinar particular, intergeniculate or inferior pulvinar, receives tectal afferents , has visuotopic map.

basal region b

in postero inferior part of thalamus place raises unsolved problems. place of endings of spinothalamic terminal axonal arborisations. spinothalamic tracts ends in 3 lateral elements , vcp, vco, , vim. secondly, ends, close these, in intralaminar-limitans elements. third place of ending, basal formation (not classical nucleus, in place attributed lower pulvinar), particular in 1 place named nucleus basalis nodalis claimed relay of pain messages layer of spinal cord. place has been shown send axons insula. in fact vcp conveys painful stimuli.

geniculate region. g

this made of 2 geniculate bodies (knee-form bodies) located ventrally @ surface of thalamus, below pulvinar. relays of highly specific functions: audition first , vision second. differentiate in ontogenesis , totally, lateral or partially medial separate thalamic mass. specialized authentical isothalamic elements.

medial geniculate nucleus gm

the nucleus geniculatus medialis receives axons auditory axons. cochlea, peripheral auditory information goes cochlear nucleus. there, through cochlear nerve, axons reach superior olivary complex of both sides. axons there constitute lateral lemniscus ends in inferior colliculus. axons inferior colliculus constitute brachium of inferior colliculus , end in medial geniculate. thalamocortical axons medial geniculate nucleus end in primary auditory cortex located in center of superior temporal plane. see auditory system.

lateral geniculate nucleus gl

the nucleus geniculatus lateralis made of different cellular strata separated lamellae, parallel surface. stratae 1 , 2, ventral, magnocellular. other mediocellular. retina, axons of optic nerves go directly geniculate nuclei. nasal component of optic nerves (the axons issued nasal field of retina of both sides) crosses @ chiasma.the axons of temporal field not cross. important in clinical neurology. after chiasma, axons form visual tracts turning around peduncles , arriving polar anterior part of geniculate nucleus. retinal axons controlateral retina end in stratae 1,4 , 6. ipsilateral retina end in 2,3 , 5. axons lateral geniculate nucleus, through optic radiation, end in primary visual cortex around calcarine fissure. see visual system.

lateral region l (or v)

this corresponds part of isothalamus located laterally medial lamina , in front of pulvinar (the noyau externe of dejerine after burdach). receives abundant , diverse infrathalamic afferences. main afferent systems occupy particular portion in lateral region. several main territories spatially separate. allows functionally significant subdivisions. other afferent systems may end in 1 or other main territories coterritories. still other can end in several main territories. topographic description of territories made using experiments in monkeys. showed no dorsal nuclei. believed dorsal posterior extension of more anterior territory. makes difficult follow terminologia anatomica (1998). follow common usage, lateral nuclei called ventral . today possible transfer data experimentally obtained in monkeys human brain using immunostaining. sequence described c. vogt (1909) hold true. starting caudally 1 may describe lemniscal territory, made of 2 components cutaneous or tactile , deep (musculoarticular), cerebellar territory made of 2 nuclei, pallidal territory , nigral territory .

gustatory territory varc

tied vcm classic arcuate nucleus (in fact heterogeneous), has neurons of own type. also, not receive lemniscal afferent , not part of vc. receives axons nucleus of solitary tract. thalamocortical neurons send axons primary gustatory area located in opercule of insula.

tactile lemniscal territory vpc=vpl+vpm

the nuclei corresponding lemniscal territory called vp. tactile part nucleus ventralis posterior caudalis vpc posterior part of lateral region, in front of pulvinar. addition of lateral nucleus vpl , of superior part of classic arcuate nucleus vpm. vpc receives axons dorsal column nuclei located in lower medulla oblongata: nucleus gracilis (goll) medial , nucleus cuneatus (burdach) lateral. starting these nuclei, axons go ventralwards , decussate (to other side) still in medulla oblongata forming lemniscal decussation . axons 2 sides form thick medial lemniscus close midline. higher, separates in order reach lower border of 2 vpc. in nucleus, axons terminate forming lamellae , somatotopic map. axons conveying information leg lateral , dorsal. conveying information mouth , tongue medial , ventral (in vpm). axonal arborisations rather small , dense. mediator of lemniscus system glutamate. thalamocortical axons of vpc send axons primary somatosensory area (areas 3b , 1) there clear somatotopic map.

deep lemniscal territory vpo (or vps)

within somesthetic nucleus, physiological maps, including in humans, have found spatial separation between representation of tactile , deep stimuli. friedman , jones (1986) designated deep region shell opposed tactile core . kaas et al. (1986) retained 1 vpo , 1 vps. present nucleus ventralis posterior oralis vpo addition of two. this, made large neurons, largest of thalamus, located in front , superior vpc. receives axons accessory cuneate nucleus of medulla. axons of nucleus conveys information muscles, tendons , joints. decussate , participate in formation of medial lemniscus. vpo receives deep information has same somatotopic map tactile. thalamocortical neurons vpo send axons in fundic area 3a (in depth of rolando sulcus) , parietal area 5.

cerebellar territory vim or vl

the nucleus ventralis intermedius receives through brachium conjunctivum axons cerebellar nuclei, more particularly dentate nucleus (percheron, 1977, asanuma et al. 1983). mediator glutamate. in primates, dentate nucleus subdivided 2 nuclei: 1 anterior , other posteroventral, first motor , other not (dum , strick, 2002). vim in fact made of 2 parts, 1 ventrolateral (viml) , 1 dorsomedian (vimm). viml (the vim of neurosurgeons) receives electively sensorimotor information. viml receives axons vestibulum , spinothalamic tract. organized according somatotopic map grossly analoguous of vpc. cortical target of viml thalamocortical neurons principally primary motor cortex (prerolandic) (schell , strick, 1984, orioli , strick, 1989) . vimm receives associative information dentate, plus tectal , spinothalamic information. organized according map, looser of viml. thalamocortical neurons send axons premotor , parietal cortex. not distinguished, there poor physiological data.

pallidal territory vo

starting cercopithecidae, 2 sources basal ganglia system medial pallidum , nigra have distinct, spatially separate, thalamic territories. pallidal territory arrives in evolution lateral addition nigal va, forming new nucleus individualized name : nucleus ventralis oralis, vo. on contrary there no more vm (which receices convergent afferences in rodents , carnivora). vo receives pallidal afferent axons medial pallidum. trajectory of pallidal afferent axons complex. axons form first ansa lenticularis , fasciculus lenticularis place axons on medial border of pallidum. there, axons cross internal capsule comb system. axons arrives @ lateral border of subthalamic nucleus. pass on h2 field of forel (1877) turn down @ h , go in h1 in direction inferior border of thalamus. distribution of pallidal axons within territory wide terminal bunches (arrechi-bouchhioua et al. 1996,1997, parent , parent, 2004 ). offers few chance fine somatotopic organization. territory stained calbindin. mediator of pallido-thalamic connection inhibitor gaba. thalamocortical neurons send axons supplementary motor area (sma), presma, premotordorsal , medial , lesser extent motor cortex.

nigral territory va

the nigral afferences come pars reticulata of substantia nigra. axons not constitute conspicuous bundle. placed medially pallidal , ascend vertically. part of territory posterior , inferior going anterior pole of central complex. part designated vm posterior continuation of nigral territory. there indeed no more vm in upper primates pallidal , nigral territories everywhere separated. in whole territory axons expand (françois et al., 2002) allowing no precise map, confirmed physiology (wichemann , kliem, 2004). va crossed mammillothalamic bundle. mediator of nigro-thalamic connection is, pallido-thalamic inhibitor gaba. in addition nigral, va receives amygdalar , tectal (superior colliculus) axons. thalamo-cortical axons go frontal cortex, cingulate cortex, premotor cortex , oculomotor fields fef , sef. important stress necessity distinguish pallidal vo , nigral va territories. fact not lead same cortical areas , systems alone 1 reason this. physiology of 2 territories different (van donkelaar et al., 1999).