Thalamus & Internal Capsule

What are the 4 divisions of the diencephalon?

1. Thalamus

2. Subthalamus

3. Epithalamus

4. Hypothalamus

What is the thalamus?

• Relay station b/w subcortical & cortical areas associated with conscious sensory perception, motor planning, cognition, memory, & emotion

• 80% of diencephalon

• Acts as selective filter for cortex

The internal medullary lamina divides the thalamus into what 3 main portions?

1. Anterior group (anterior nucleus)

2. Medial group (dorsomedial nucleus)

3. Lateral group (dorsal/ventral tiers)

What is the subthalamus?

Relay station b/w basal nuclei & cortical areas to regulate motor activity

What is the epithalamus?

Relay station b/w subcortical & cortical areas regulating limbic system & circadian rhythms

What is the hypothalamus?

Relay station b/w subcortical & cortical areas regulating limbic system & ANS for control of visceral function

What do relay nuclei do?

• Convey info from sensory systems, basal nuclei, & cerebellum to cortex

• Send info to specific, localized areas

• Found in ventral tier of lateral nuclear group

What do association nuclei do?

• Process emotional & some memory info

• Integrate different types of sensations

• Connect reciprocally with large areas of cortex

• Found in anterior, medial, & dorsal tier of lateral thalamus

What do nonspecific nuclei do?

• Regulate consciousness, arousal, & attention

• Receive multiple types of inputs & project to widespread areas of cortex

• Found in midline, reticular, & intralaminar nuclei

Describe the anterior group of the thalamus.

• Anterior nucleus

• Function → attention, memory, & emotions (limbic)

• Afferent → info from mammilothalamic tract, hippocampus

• Efferent → sends info to cingulate gyrus

Describe the medial group of the thalamus.

• Dorsomedial nucleus

• Function → “gut feelings”, memory, affect, foresight, goal-directed behavior

• Afferent → info from prefrontal cortex, olfactory, & limbic structures

• Efferent → sends info to prefrontal cortex

Describe the intralaminar nuclei of the thalamus.

• Centromedian & parafascicular nucleus

• Function → arousal & attention

• Afferent → info from ascending reticular system

• Efferent → sends info to many areas of cortex

Describe the reticular nucleus of the thalamus.

• Does NOT send info to the cortex

• Sends inhibitory (GABA) projections to other thalamic nuclei

• Functions → adjusts thalamic activity

• Afferent → info from cortex & thalamic projection neurons

• Efferent → sends info to other thalamic nuclei

Describe the lateral group (dorsal tier) of the thalamus.

• Lateral dorsal nucleus (LD) → memory

  • Afferent → hippocampus

  • Efferent → cingulate gyrus

• Lateral posterior nucleus (LP) → sensory integration

  • Reciprocal afferent/efferent w/ parietal lobe

• Pulvinar nucleus → sensory integration

  • Reciprocal afferent/efferent w/ parietal, occipital, temporal lobes

Describe the lateral group (ventral tier) of the thalamus.

• Ventral anterior nucleus (VA) → motor

  • Afferent → basal nuclei

  • Efferent → motor planning areas

• Ventral lateral nucleus (VL) → motor

  • Afferent → cerebellum

  • Efferent → motor cortex, motor planning areas

• Ventral posterior medial nucleus (VPM) → relay somatosensory of head

• Ventral posterior lateral nucleus (VPL) → relay somatosensory of body

What are the geniculate nuclei?

• Lateral Geniculate Nucleus (LGN) → “light”

  • Relay for visual info

• Medial Geniculate Nucleus (MGN) → “music”

  • Relay for auditory info

Where does majority of the blood supply for the thalamus come from?

Posterior cerebral artery (PCA)

What impairments come from lesions to the ventral thalamus (VA & VL)?

• Contralateral chorea, athetosis, ballismus

• Hypotonia or contralateral limb ataxia

What impairments come from lesions to the ventral posterior thalamus (VPM & VPL)?

• Initial contralateral hemianesthesia

• Later thalamic pain

What impairments come from lesions to the lateral geniculate (LGN)?

• Visual processing dificulty

• Hemianopsia

What impairments come from lesions to the anterior nuclei?

• Emotional lability

• Not in control of emotions

What impairments come from lesions to the dorsomedial nucleus?

• Decreased affect

• Loss of facial expression indicating mood

• Inability to express emotions

Where is the internal capsule located?

• Surrounded by lentiform nucleus (laterally) & thalamus and head of caudate nucleus (medially)

• Fibers fan out as corona radiata

What are the 5 divisions of the internal capsule?

1. Anterior Limb

2. Posterior Limb

3. Genu

4. Retrolenticular part

5. Sublenticular part

Describe the anterior limb of the IC.

• Carries info from ant nucleus of thalamus → cingulate gyrus

  • Attention, emotions, & memory

• Carries info from dorsomedial nucleus of thalamus → prefrontal cortex

  • Memory, affect, foresight, & goal-directed behavior

Describe the posterior limb of the IC.

• Carries info from VA & VL nuclei → premotor/primary motor cortex

  • Motor info from cerebellum/basal ganglia

• Carries CST & CBT fibers → brainstem & SC

• Carries info from VPL & VPM → primary somatosensory cortex

Describe the genu of the IC.

• Additional frontopontine fibers

• Additional fibers connecting VA & VL with premotor & primary motor cortex

Describe the retrolenticular part of the IC.

• Pulvinar/LP ←→ Parieto-occipital-temporal association cortex

  • Sensory integration

• LGN → primary visual cortex

  • Part of optic radiation

• Parietal lobe → pons

  • Corticopontine fibers

Describe the sublenticular part of the IC.

• Runs continuous w/ retrolenticular

• LGN → primary visual cortex

  • Part of optic radiation

• MGN → primary auditory cortex

Where does the blood supply of the IC come from?

• Middle Cerebral Artery (MCA)

• Internal Carotid

• Anterior Cerebral Artery (ACA)

What impairments are caused by lesions to the posterior limb of the IC?

• Contralateral impairments

• Motor → spastic paralysis, CN dysfunction

• Sensory → hemianesthesia, thalamic pain

What impairments are caused by lesions to the anterior limb of the IC?

• Cognitive fatigue (mental exhaustion) → behavior changes

• Psychiatric symptoms → OCD

What impairments are caused by lesions to the retrolenticular & sublenticular parts of the IC?

Contralateral hemianopsia