Thalamus

KC 6 The thalamus relays subcortical input to the cortex, but also performs...

synthesis and integration functions, participating in enhancing or diminishing the signal. and degrees of cortical arousal

Clinical considerations Thalamic pathology can cause- Both abnormal voluntary and involuntary movements can occur with

thalamic pathology

KC 2 The thalamus is closely interconnected with the cerebral cortex, sending ...

thalamocortical axons to a part of the cortex and receiving corticothalamic axons in return

Clinical considerations Thalamic pathology can cause- Memory impairments can occur w/ thalamic pathology, the most notable being...

the alcoholic-Korsakoff or Wernicke-Korsakoff syndrome -damge occurs to the MD and REN and may or may not have accompanying mammillary body damage -thiamine deficiency accompanies this illness

KC 10 The thalamus plays a role in emotional behavior via interconnections with...

the limbic cortices (cingulated and parahippocampal cortex) thereby having a role in memory, mood, and motivation

KC 13 The Dejerine-Roussy or thalamic pain syndrome can occur with strokes involving...

the posterior and ventral part of the thalamus

Reticular nucleus of the thalamus Cholinergic brainstem and basal forebrain input into the reticular nucleus is thought to switch its mode from...

the short bursts of deep sleep to the tonic sustained mode of wakefulness -not working when sleep walking

Clinical considerations Thalamic pathology can cause- Contralateral hemianesthesia (loss of sensation on one side of body, loss of pain and temperature on opposite side), hemihypoancusis (decreased sensitivity to sound stimuli), and contralateral hemianopsia (decreased vision or blindness in half of visual field) can occur if...

the thalamic relay nuclei of the somatosensory auditory or visual pathways are damage (VA and VL)

Reticular nucleus of the thalamus During wakefulness...

tonic low frequency activity is observed

Blood supply

-mainly from the top of the basilar artery and proximal PCAs -paramedian branches arising from the top of the basilar artery

Intro Thalamus

-nearly all pathways that project to the cortex do so via synaptic pathways in the thalamus -major sensory relay station -conveys nearly all other inputs to the cortex -including: cerebellum and basal ganglia, limbic inputs, modulatory inputs involved in arousal and sleep- wake cycles and others -nuclei of thalamus have reciprocal feedback connections from the cortical areas they project

KC 7 The reticular nucleus participates in sleep by...

disengaging the cortex from sensory channels

KC 4 The reticular nucleus is the only thalamic nucleus that...

does not project to the cortex

KC 9 The thalamus plays a role in associative functions by being...

interconnected with cortical areas that play a role in complex thought, attention, decision making and higher mental processes including language

Functions and connections of key thalamic nuclei SENSORY specific thalamic nuclei- relay nuclei (all w/ reciprocal thalamocortical and return corticothalamic connections)

*sensory information from all modalities is brought to the level of conscious perception via these thalamocortical projections

Association specific nuclei- relay nuclei (all w/ reciprocal thalamocortical and corticothalamic connections) Pulvinar nucleus

- receives superior colliculus output -projects to the visual association cortex of the occipital and temporal lobes and visually relate parts of the parietal lobe

Topography of Thalamus: thalamus is part of the diencephalon Laterally

-bounded by its external medullary lamina between thalamic gray matter and the white matter or axons of the posterior limb of the internal capsule -the thalamic reticular nucleus is embedded in the external medullary lamina external medullary lamina= white matter bundles that carry ascending axon from the thalamus to the cortex via the internal capsule, and has descending axons from the cortex to the thalamus

Topography of Thalamus: thalamus is part of the diencephalon Anteriorly

-bounded by the foramen of Munro -and the bulge of tissue immediately posterior to the fornix- its anterior nucleus

Topography of Thalamus: thalamus is part of the diencephalon Ventrally

-bounded by the groove known as the hypothalamic sulcus

Left Thalamus damage: VPL and VPM damaged by stroke

-clinical signs 3-5 in terms of mechanisms seem paradoxical and are not understood -may take time (2-3 weeks) to develop

Topography of Thalamus: thalamus is part of the diencephalon Dorsally

-forms the floor of the body of the lateral ventricle

Topography of Thalamus: thalamus is part of the diencephalon Posteriorly

-in direct continuity with the midbrain tegmentum -junction is overlaid by the large pulvinar nucleus of the thalamus

Limbic specific nuclei- relay nuclei (w/ specific thalamocortical and corticothalamic connections) Anterior

-receives input from the mammillary body of hypothalamus (mammillothalamic tract) and hippocampus (via fimbria-fornix) -projects to cingulate and parahippocampal cortex

Association specific nuclei- relay nuclei (all w/ reciprocal thalamocortical and corticothalamic connections) Dorsomedial nuclei (DM)

-receives olfactory, basal forebrain, hypothalamic and amygdale input -projects to prefrontal cortex (i.e. the association cortex anterior to the motor cortex that forms the frontal pole and orbitofrontal part of the frontal lobe) -clinical note: sever connection b/w dorsomedial nuclei and prefrontal cortex

Functions and connections of key thalamic nuclei SENSORY specific thalamic nuclei- relay nuclei (all w/ reciprocal thalamocortical and return corticothalamic connections) Ventral posterior lateral nucleus (VPL)

-receives spinothalamic tract and medial lemniscus information -projects to the non-face parts of the post-central gyrus (now all the sensory fibers from the STT and DCML are all traveling together)

Functions and connections of key thalamic nuclei SENSORY specific thalamic nuclei- relay nuclei (all w/ reciprocal thalamocortical and return corticothalamic connections) Medial geniculate nucleus (MGN)

-receives the axons from the auditory system of the brachium of the inferior colliculus -gives rise to the acoustic radiation that ends is Heschl's gyrus

Functions and connections of key thalamic nuclei MOTOR specific thalamic nuclei- relay nuclei (all w/ reciprocal thalamocortical and corticothalamic connections) Ventral lateral (VL)

-receives the output of contralateral deep cerebellar nuclei (mainly dentate nucleus) -projects to the motor cortex of the precentral gyrus

Functions and connections of key thalamic nuclei SENSORY specific thalamic nuclei- relay nuclei (all w/ reciprocal thalamocortical and return corticothalamic connections) Lateral geniculate nucleus (LGN)

-receives the output of retinal ganglion cells from the ipsilateral temporal retina and contralateral nasal retina -gives rise to the optic radiation which ends in the calcarine cortex above (cuneus) and below (lingual gyrus) the calcarine fissure -FYI retinal input from the nasal retina ends on LGN layers 1,4, and 6 and that form the temporal retina on layers 2,3, and 5. This nucleus is the only one that is laminated

Functions and connections of key thalamic nuclei MOTOR specific thalamic nuclei- relay nuclei (all w/ reciprocal thalamocortical and corticothalamic connections) Ventral anterior (VA)

-receives the output of the ipsilateral basal ganglia -projects to premotor and frontal eye field cortex

Functions and connections of key thalamic nuclei SENSORY specific thalamic nuclei- relay nuclei (all w/ reciprocal thalamocortical and return corticothalamic connections) Ventral posterior medial nucleus (VPM)

-recieves the trigeminal lemniscus (ventral and dorsal trigeminal thalamic tracts) which carries sensory information from the head and face -projects to the face part of the post central gyrus

Left Thalamus damage: VPL and VPM damaged by stroke Key point clinically and therapeutically is that these clinical signs are diagnostic for...

-thalamic pathology in the brain contralateral to the face and body side where somatosensory changes occur -and the pt is miserable, possibly facing a long regimen of analgesic medication which is some instances may not proved relief

Clinical considerations

-thalamus not immune from neurological diseases -pin-pointing their clinical correlates is always a challenge -sensory, motor, association, and limbic nuclei are adjacent to each other in many locations and may share a common vascular supply -axon bundles carrying specific info may pass through or b/w nuclei concerned w/ other functions -proximity of the hypothalamus may impose endocrine abnormalities if damaged

Topography of Thalamus: thalamus is part of the diencephalon Medially

-the thalami of each hemisphere are separated by the 3rd ventricle -in 70% of human brains a bride known as the mass intermedia or inter thalamic adhesion connects across the midline

Clinical considerations Thalamic pathology can cause- Somatosensory changes following pathology in the posterior and ventral thalamus are both complex and diagnostic damage to this part of the brain

-this complex is known as Dejerine-Roussy or thalamic pain syndrome

Thalamic divisions and nuclear groupings The ovoid shaped thalamus can be divided into 2 tiers

1. Dorsal tier of nuclei (pulvinar nucleus) 2. Ventral tier of nuclei (sensory and motor ventral nuclei= VA, VL, VPM, VPL) *don't worry about LD and LP 3. also divided into relay, intralaminar, and reticular nuclei (discussed in more detail in text)

Left Thalamus damage: VPL and VPM damaged by stroke explanations:

1. few surviving and/or damaged neurons in the injured left thalamus are sending abnormal messages to the cortex 2. there may be pathways not know carrying info that bypasses the somatosensory thalamus (VPL+VPM) 3. peripheral stimuli to tissue receptors may trigger dual (1) somatosensory messages such as pain, temp, and touch and (2) emotional message -somatosensory message is altered by thalamic damage -emotional message is perceived in other brain areas not damaged

Reticular nucleus of the thalamus

= the GATEKEEPER OF THE THALAMUS -provides GABAergic inhibitory input to all thalamic nuclei -does NOT project to the cortex -receives collaterals of corticothalamic axons and collaterals of thalamocortical axons *in a perfect position to monitor both cortex and thalamus

Dorsomedial nuclei

Input: amygdala, olfactory cortex, basal ganglia Output: prefrontal cortex

Ventral Lateral nucleus:

Input: deep cerebellar nuclei Output: motor and premotor cortex

Medial Geniculate nucleus:

Input: inferior colliculus Output: auditory cortex

Anterior nucleus

Input: mamillothalamic tract, fornix Output: cingulate gyrus

Ventral Lateral Posterior nucleus:

Input: medial lemiscus and spinaltholamic tracts Output: somatosensory cortex

Lateral Geniculate nucleus:

Input: optic tract Output: visual cortex

Ventral Anterior nucleus

Input: substantia nigra, pars reticulata, internal globus pallidus Output: frontal cortex

Pulvinar:

Input: superior colliculus Output: parieto-occipital cortex

Ventral Medial Posterior nucleus:

Input: trigeminal lemniscus, trigeminothalamic tract, gustatory inputs Outputs: somatosensory cortex

Left Thalamus damage: VPL and VPM damaged by stroke=>

Right face and body clinical signs 1. hemianesthesis=loss of sensation on one side of body, loss of pain and temperature on opposite side 2. asterognosis= lack of ability to recognize objects in hands 3. paroxysmal pain= severe pain and intolerable occurring spontaneously 4. dysesthesia= highly unpleasant emotional reactions to tactile or temperature stimuli that may not be perceived or only slightly perceived 5. hyperpathia= painful reactions to minor stimuli such as pressure or light touch, and from clothing

Reticular nucleus of the thalamus During deep sleep the cortex is...

disengaged from sensory input with only occasional short bursts of activity

KC 8 The thalamus is an integral structure for the...

basal ganglia and cerebellum in motor behavior

*** Basal Ganglia disease (i.e. hemorrhage) is always expressed...

contralaterally (ipsilateral basal ganglia to ipsilateral premotor cortex-but the output of the motor cortex decussates)

***Cerebellar disease is always expressed...

ipsilaterally (deep cerebellar output to VL, then VL projects to motor cortex but its output (corticospinal tract) decussates back to ipsilateral side)

Key Concept 1 Thalamus is the largest component...

of the diencephalon

KC 11 Clinical signs from thalamic strokes and vascular abnormalities are complex...

reflecting that the vascular territories from penetrating vessels overlap and many functions may be compromised

KC 12 The motor nuclei of the thalamus have been targets for lesion and stimulation studies aimed at...

relieving tremor in Parkinsonism and the debilitating coactivation of extensors and flexors in dystonia

KC 5 The reticular nucleus governs the flow of activity through the thalamus by...

sending inhibitory projections to all thalamic nuclei

KC 3 The thalamus is functionally diverse...

with distinct sensory, motor, associative limbic parts