Thalamus & Thalamocortical Relationships Flashcards
How are the thalamus on each side connected?
Thalamic adhesion (massa intermedia)
What are the thalamic relay nuclei (two sensory and two motor)?
Sensory:
VPL and VPM
Motor:
VA (to 6) and VL (to 4)
These project to a specific cortical area?
What are thalamic association nuclei?
These connect diffusely to multiple cortical and subcortical areas
What are all the thalamic association nuclei?
- Anterior (ANT)
- Dorsomedial (DM)
- Intralaminar (CM-PF)
- Pulvinar (PULV)
What does the epithalamus include?
Pineal body and habenula
What does the metathalamus include?
Medial and lateral geniculate nucleus
What separates the thalamus from the hypothalamus?
Hypothalamic sulcus
What divides the thalamus along its anterior-posterior axis and what is embedded in it?
Internal Medullary Lamina, includes the intralaminar nuclei. This is a myelinated axon bundle
What myelinated axon band surrounds the alteral surface of the thalamus, and what is lateral to it?
External Medullary Lamina. Lateral to it is the thalamic Reticular Nucleus
Is the thalamus lateral or medial to the posterior limb of the internal capsule? How does it relate to the ventricles?
Medial to posterior limb of internal capsule, inferior to the lateral ventricle, lateral to the third ventricle
How do you differentiate between VA and VL thalamus?
VL thalamus will be found when there are three thalamic nuclei visible, including the small Lateral Dorsal nucleus (midthalamic level)
What three nuclei are present at the mid-thalamic level? What is present here most ventrally?
LD, VL, and DM
Most ventrally, the mamillary bodies will be present here
What does VL thalamus do?
Relays basal ganglia and cerebellar motor information to primary motor cortex (area 4) for fine regulation of voluntary movement
What does VA thalamus do?
Relays basal ganglia information to premotor cortex where motor programs are stored (area 6)
Where do ANT/LD thalamus project to?
Cingulate cortex - for limbic system
Where does DM thalamus project to? Where does it receive input from?
How large is it?
Receives input from prefrontal cortex and amygdala, projects to prefrontal cortex
2nd largest thalamic nucleus, behind pulvinar
Where does LP/PULV receive input from, and which one is primary? Where does PULV project to?
Input from retina, superior colliculus, and visual cortex. Primary is visual cortex.
PULV projects to parieto-temporal-occipital cortices.
What is the primary cortical regulator of thalamocortical rhythmicity?
Reticular Thalamic Nucleus. This receives input from the cortex and projects to the thalamus, but thalamus to does not project to it
What causes thalamocortical dysrhythmia?
Loss / alteration of afferent input to the thalamus, including reticular thalamic nucleus, cerebral cortex, cerebellum, spinal cord / brainstem, or basal ganglia
What is the postulated underlying cause of Parkinsonian tremors, intention tremors, or chronic intractible pain? How is it corrected?
Dysrhythmias due to loss of afferent input into the thalamus, causing thalamocortical dysrhythmia (TCD)
It is corrected via stereotaxic thalatomy or deep brain stimulation
What causes the difference between an action tremor and a resting tremor?
Cerebellar vs GPi/SNr projections to the thalamus disrupt the rhythmicity of different motor thalamic cell populations.
Where is Vim and what is it?
Ventral intermediate nucleus, located in ventrocaudal region of VL. It is the “muscle sensor” which picks up unconscious proprioceptive information from the efferents of cerebellum (via DSCT).
What is Vim’s role in the firing rates of action vs resting tremors?
Vim cells have firing rates that are timelocked with peripheral tremors in patients with parkinson’s disease or essential tremor (a type of action tremor).
This is the nucleus that is targeted for surgical lesions (thalatomy) or deep brain stimulation.
What can cause thalamic pain syndrome?
Any disruption of the ventral posterior (VP) thalamus, including tearing away of brachial / lumbosacral plexuses, herpes neuralgia, SCI, or strokes.
This results in TCD in CM-PF and CL nuclei which are involved in the limbic system transmitting pain.
What is the CL nucleus? (central lateral) Where does it receive info from and give output to?
An intralaminar nucleus along the lateral edge of the DM thalamus.
It receives info from lamina X spinal neurons which carry viscerosensory information (organ afferents).
It projects to the limbic association and insular cortexes for mediating emotional responses to pain.
CL thalatomy has been shown to help with chronic intractable pain.
What releases histamine into the telencephalon and diencephalon?
Hypothalamus
What nuclei in the thalamus are particularly sensitive to arousal, and project to the cortex / BG?
Intralaminar thalamus (CM-PF, CL), sensitive to arousal via locus ceruleus, raphe nuclei, PPN (ACh), and hypothalamus.
They project to the cortex for arousal and alertness, and the basal ganglia via the thalamostriatal projections
What do lesions of the intralaminar thalamus cause? Unilateral or bilateral?
Altered states of consciousness (acute mania, delirium).
Unilateral = Hemispatial unawareness Bilateral = Coma
How does the hippocampus communicate with the thalamus for memory information?
Hippocampus projects to mammillary body.
Mammillary body projects ANT nucleus of thalamus via mammillothalamic tract
What lesion will cause severe memory deficits and what is one cause?
Lesion to anterior nucleus of thalamus, mammillary bodies, or mammillothalamic tract.
One cause: Korsakoff’s psychosis due to B1 deficiency
Since LD thalamus is the partner to ANT thalamus, what is its function in memory?
No direct connection to the mammillary bodies, however, it connects to the parietal cortex and functions in memory related to spatial navigation
What is the function of the DM thalamus with relation to the limbic system?
Communicates with amygdala and prefrontal cortex for emotional processing. Lesions will decrease emotional responses.
What is the function of the DM thalamus with relation to the eye movements?
It stabilizes the visual perception during eye movements, especially saccadic ones.
Superior colliculus sends copy of image to FEF via the DM thalamus, and then FEF determines which way to move eyes in saccades.
What is the general function of the pulvinar?
Functions in visual awareness and maintenance of visual attentiveness to a particular feature in a visual scene
What will people with PULV damage experience difficulty with?
Temporal visual attentiveness problems, which is needed to focus on a second visual target of behavioral relevance after already being attentive to a first object
What is the most common cause of thalamic damage?
Hemorrhagic stroke
What two arteries supply thalamus?
- Posterior communicating artery
2. Posterior cerebral artery
Why do thalamic strokes imitate other types of strokes?
Vascular accidents overlap a number of functional areas and produce a mixture of symptoms
What thalamic nuclei do “Polar Zone” hemorrhagic strokes affect, and what are the patient’s symptoms?
Affects VA / ANT nuclei. This causes problems with executive motor programs for area 6 (apraxia), and memory due to ANT (disorientation)
What thalamic nuclei do “Thalamo-Perforating Zone” hemorrhagic strokes affect, and what are the patient’s symptoms?
Affects DM and intralaminar thalamic nuclei. Produces decreased arousal and coma if bilateral (intrathalamic nuclei). Patients can show personality changes like apathy or agitation (DM), also impaired orientation and confusion
What thalamic nuclei do “Thalamo-Geniculate Zone” hemorrhagic strokes affect, and what are the patient’s symptoms?
Affects VP and VL regions, infarcts produce abnormal pain and temperature sensitivity (VP), plus variable motor signs including ataxia and chorea (VL)
What thalamic nuclei do “Posterior Choroid Zone” hemorrhagic strokes affect, and what are the patient’s symptoms?
Affects caudal CM-PF and PULV. This is relatively rare, but will lead to arousal problems and visual deficits, with varying motor deficits due to Vim, especially if it spreads to posterior limb of internal capsule.
