Thalamus

Describe the Thalamus

• Comprised of?

• Function?

Comprised of:

• dorsal thalamus + thalamic reticular nucleus (ReT)

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Functions:

• Conveys Info (highway)

  • sensory pathways → cerebral cortex

    • (except for olfaction)

  • Lower centers → cerebral cortext

    • Lower centers ex: basal ganglia, cerebellum, hypothalamus

  • To areas involved in attention and executive functions.

• Gate transfer of info to cerebral cortex

• Coordinates cortical arousal

Describe the connections between the thalamus and the cortex projections

Thalamus Nuclei (except ReT) and Cerebral Cortext = reciprocally connected

• Via Excitatory projection neurons

• Corticothalamic fibers → individual thalamic nuclei

  • modulatory inputs (info processing)

• Corticothalamic > thalamocortical projections

Draw out the thalamic nuclei

Describe the Differences between specific and non-specific:

• Function

• Electrical stimulation produces?

Specific Vs Non

• Specific

  • send efferent (thalamocortical fibers) → specific functional cerebral cortical areas → relay information to these areas.

  • Electrical stimulation → rapid, localized responses in ipsilateral cortex.

• Non-specific

  • send efferent → widespread areas of cortex → more generalized cortical activation.

  • Electrical stimulation: → widespread activity in both hemispheres w/ longer time delay.

What are Relay Nuclei?

• A/E?

• Location

• Consists of?

Relay Nuclei:

• type of specific nuclei

• A/E:

  • A: subcortical inputs ( sensory pathways, cerebellum, basal nuclei, mammillary bodies)

  • E: primary cortical areas (e.g., Sl, VI, MI)

    • represent final segment of pathways conveying sensory info to cortex

• Location:

  • Anterior/Lat. Thalamus

• Consist of:

  • Ventral Posterior nucleus: Somatosensory

  • Lateral Geniculate Nucleus: Vision

  • Medial Geniculate Nucleus: Audition

Describe the Ventral Posterior Complex (VP):

• VPL vs VPM’s site of termination

• Projects to? location?

VP:

• VPL (ventralpostolateral):

  • site of termination of the somatosensory pathways of the body

• VPM (ventralposteromedial):

  • site of termination for trigeminothalamic pathways (face/oral cavity)

• Projects to:

  • primary somatosensory cortex (Sl)

    • in postcentral gyrus and posterior paracentral gryus of the parietal lobe.

Describe the VPI

• Location

• Function

• Projections

ventral posterior inferior nucleus (VPI)

• Location: small area in between VPL and VPM

• Function: receive vestibular information (oral part of VPL also receives this)

• Projections:

  • to parieto-insular vestibular cortex (PIVC) @ posterior end of the insula

  • Vestibular Cortex of parietal lobe

    • @ depths of the central sulcus (3a)

    • @ rostral tip of the intraparietal sulcus (2v).

Describe the VPMpc

• AKA?

• Afferent

• Efferents?

medial parvicellular portion of the ventral posteromedial nucleus (VPMpc)-

• AKA: ventromedial basal (VMb) nucleus-

• Afferents:

  • info from solitary nucleus

    • Taste (directly)

    • GVA (via parabrachial nucleus)

      • NOTE: parabrachial nucleus surrounds the SCP in dorsal lat. Pons

• Efferents:

  • Taste:

    • Conveyed to gustatory cortex of the inner frontal operculum and insula

  • GVA:

    • to Insula

    • GI tract, cardiovascular input, and respiratory input represented sequentially caudal to the taste representation.

Describe the VMpo

ventromedial posterior thalamic nucleus (VMpo)

• Location: More caudally in ventral medial thalamus

• Afferent:

  • Pain/Temp from Anterolateral Tract

• Efferent:

  • projects to dorsal posterior insula

  • caudal to the viscerosensory representation in the insula

What is the interoceptive Cortext?

The dorsal insula receiving input from VMb and VMpo can be considered "interoceptive cortex" representing the physiological condition of the body.

What constitutes the metathalamus?

The lateral and medial geniculate bodies constitute the metathalamus and may be considered the caudal continuation of the ventral nuclear mass of the lateral thalamus.

Describe the LGN:

• Location

• A/E

Describe the MGN:

• A/E

Lateral Geniculate Nucleus (LGN):

• Location:

  • small, rostrolaterally directed projection from the posterior thalamus

• A/E:

  • A: Receives input from the retina of both eyes

  • E:projects to the primary visual cortex (VI)

    • Found on banks of the calcarine sulcus on the medial surface of the occipital lobe

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Medial Geniculate Nucleus (MGN):

• A/E:

  • A: from inferior colliculus via its brachium

  • E: primary auditory cortex (A1) associated with the transverse temporal gyri of Heschl

List the nuclei associated w/ the motor relay nuclei of thalamus

• Ventral Anterior nucleus (VA)

• Ventral Lateral nucleus (VL)

Describe the VA

• A/E

• Function?

ventral anterior nucleus (VA)

• Afferents:

  • basal nuclei

  • internal segment of the globus pallidus

    • Targets parvocellular parts of VA

  • pars reticulata

    • Targets medial magnocellular part

• Efferent:

  • frontal eye fields (BA 8) and the prefrontal cortex

• Function:

  • Contributes to loop circuits of basal nuclei system (oculomotor, motor, associative)

  • Involved in motor planning and behavior.

Describe the VL

• Afferent?

• VLO vs VLp:

  • A/E

  • Function

ventral lateral nucleus (VL)

• Afferent:

  • basal nuclei and the cerebellum.

• VLO (VLa)

  • Rostral part of VL

  • A/E:

    • A: GPi

    • E: premotor cortices, including SMA.

  • Function:

    • Contributes to motor loop circuit of basal nuclei, involved in motor planning.

• VLp:

  • Caudal Portion

  • A/E:

    • A: deep nuclei of the cerebellum

    • E: primary motor cortex

  • Function:

    • Contributes to cerebellar circuits for modulating motor activities, e.g., limb movements.

Describe the Limbic Nuclei

• Function

• Consists of?

Limbic Nuclei:

• Function:

  • contribute to memory circuitry of the limbic system.

    • (Circuit of Papez)

• Consists Of:

  • Anterior nuclear group

    • NOTE: LD nucleus can be considered a dorsal extension of the anterior nucleus and has similar limbic connections.

  • Lateral dorsal nucleus (LD)

Describe the Anterior Nuclear Group

• Comprised of?

• Location

• A/E

anterior nuclear group

• Comprised of:

  • three nuclei enclosed by the split internal medullary lamina

    • NOTE: refered collectively as anterior nucleus

• Location:

  • caudal lateral to the interventricular foramen

• A/E:

  • A: hippocampal formation

    • Via fornix/Mammillary bodies (mammilothalamic tract)

  • E: cingulate cortex of the limbic lobe

Describe Association Nuclei

• Function

• Location

• Properties

• Comprised of?

Association nuclei (higher- order relay)

• Function:

  • send projections to association cortices (e.g., parieto-occipital, prefrontal) and relay information from primary cortical areas, as well as subcortical inputs.

• Location:

  • medial thalamus and posterior part of the dorsal thalamus.

• Properties:

  • Largest Nuclei of Thalamus

  • Strong reciprocal connections

• Comprised of:

  • Mediodorsal nucleus (MD)

  • Pulivinar

  • Lateral Posterior nucleus

Describe MD

• Function

• A/E

• Damage =?

mediodorsal nucleus

• Function:

  • Involved in: attention, decision making, behavioral planning

  • Via connections w/ amygdala interfaces with emotion networks of the limbic system

• A/E:

  • A: amygdala, olfactory cortex, entorhinal cortex, substantia nigra, and anterolateral system.

  • E: entire prefrontal cortext (reciprocal)

    • Including FEF and Anterior cingulate cortext

• Damage =:

  • executive functions (e.g., judgement, decision making)

  • affective behaviors.

Describe LP

• Location

• A/E

• Function

Pulvinar and Lateral posterior nucleus (LP):

• Location:

  • back of the thalamus dorsal and lateral to the midbrain.

  • merges w/ pulvinar and its caudal borders are difficult to distinguish.

  • commonly considered with the pulvinar.

  • Consists of 4 subnuclei

• A/E:

  • A:

    • superior colliculus

    • pretectum

    • visual cortex of occipital lobe (vision related)

    • unimodal sensory and association cortices of the parietal and temporal lobe.

  • E:

    • multimodal association cortices of the posterior parietal lobe and lateral temporal lobe.

• Function: spatial attention

Describe the Gating Function of the Thalamus:

• Describe the Two Gates

• What happens in non-REM sleep vs Wakefullness

Gating Function:

• Two Gates:

  • Tonic Mode:

    • During Wakefullnes/REM sleep:

    • thalamocortical relay neurons = slightly depolarized via modulatory inputs → tonic discharge → transfer into to cortex

  • Burst Mode:

    • relay neurons = hyperpolarized via inhibitory input from the ReT or withdrawal of excitatory inputs from brainstem → Bursting discharge → functional disconnection between thalamic inputs and thalamocortical projections

Non-REM sleep vs Wakefullness:

• Non-REM: rhythmic burst discharge,

• Wakefullness: many relay neurons remain in burst mode; but . Arrhythmic burst activity is proposed to increase the signal-to-noise ratio and allow these neurons to participate in detection of novel stimuli

  • Presumably, focusing attention and analysis of stimulus features would involve a switch to tonic mode.

Describe Non-specific Nuclei:

• Described as?

• Comprised of?

Non-specific Nuclei:

• traditionally described as having diffuse projections to cerebral cortex Nuclei

• Comprised of:

  • Midline nuclei (ex: paratenial nucleus and nucleus reuniens)

  • Intralaminar nuclei

Describe the midline nuclei

• Properties

• A/E

• Reciprocally connected to?

• Function

midline nuclei

• Properties:

  • small and difficult to distinguish in humans and relatively poorly understood.

• A/E:

  • A: hypothalamus, basal forebrain, and brainstem reticular formation.

  • E: ventral striatum and amydala.

• Reciprocally connected to:

  • Limbic cortex (anterior cingulate cortex, entorhinal cortex) and the hippocampus

• Function:

  • connections of the midline nuclei suggest limbic functions.

Describe the IL:

• Location

• Caudal Group

  • Consists of?

  • Afferent?

  • Function

• Rostral Group

  • Afferent

  • Function

• Efferent

Intralaminar nuclei:

• Location:

  • surrounded by the internal medullary lamina

• Caudal Group:

  • Consists of centromedian nucleus (CM) and parafascicular nucleus (Pf)

  • Afferent:

    • GPi (largely collaterals of projections to VLO).

  • Function:

    • participates in basal nuclei circuitry;

      • Increases excitability of cortical + striatal neurons → cortico-basal nuclear-thalamocortical loop circuits

• Rostral Group:

  • Afferent:

    • elements of ascending reticular activing system + anterolateral system and cerebellum

  • Function:

    • regulating the level of arousal and cognitive alertness

      • IE: an arousal and alerting function.

• Efferent:

  • striatum and widespread areas of cerebral cortex

Describe ReT:

• Properites

• Afferent

• Key Difference

• Function

Reticular nucleus (ReT):

• Properties:

  • Derivative of ventral thalamus

  • Contain GABAergic neurons that project to all thalamic nuclei

• Afferent:

  • collaterals from thalamocortical and corticothalamic projection neurons

• Key Difference:

  • Unlike nuclei of the dorsal thalamus, does NOT project to the cerebral cortex.

• Function:

  • Gates activity of neurons within thalamic nuclei e.g., related to saliency or focusing on a sensory or motor modality.

  • Important for synchronization of cortical activity during (Non-REM) sleep; contributing to sleep spindle and delta wave activity.

Describe the thalamic radiations

• What is it?

• Types

• Projects through?

Describe the four thalamic radiations:

• Consists of?

• Travels Through?

Thalamic Radiations:

• What is it?:

  • fibers connecting the thalamus with the cerebral cortex

• Types:

  • Anterior thalamic radiation

  • Superior thalamic radiation

  • Posterior thalamic radiation

  • Inferior thalamic radiation

• Projects through Internal Capsule

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Anterior Radiation:

• Consists of:

  • fibers connecting MD and anterior nucleus w/ frontal lobe and cingulate cortex.

• Travels Through:

  • anterior limb of internal capsule

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Superior Radiation:

• Consists of

  • fibers connecting VP w/ parietal lobe and VA-VL w/ frontal lobe.

• Travels through

  • posterior limb of internal capsule.

NOTE: May also be referred to as the central thalamic radiation.

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Posterior Radiation: •

• Consist of:

  • fibers connecting LGN w/occipital lobe (geniculocalcarine tract- optic radiations)

• Travels Through:

  • retrolenticular part of the internal capsule

Note: Also, contains pulvinar projections to the occipital lobe and posterior parietal lobe.

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Inferior Radiation:

• Consists of

  • fibers connecting the MGN w/ temporal lobe (auditory radiations).

• Travels through

  • sublenticular part of internal capsule.

Note: Also, contains pulvinar projections to the temporal lobe.