THALAMUS This course outline is designed to provide you with a study guide. Use the lecture, book, and other resources to expand on its contents.

Lesson Objectives

1. Describe the function of the archithalamic nuclei.

2. Describe the function of the neothalamic nuclei.

3. Explain the function of the intralaminar and reticular nuclei.

4. What are the intrinsic nuclei of the thalamus and how do they function differently from the other groups.

5. Describe the primary input from the thalamus to the prefrontal cortex and discuss the function.

6. How might the thalamus function as an integrative system similar to the cortex?

Functional Subdivisions

(forms 80% of diencephalon)

Archithalamus:

• Oldest;
• Animals with rudimentary cortex;
• Sense of smell;
  • Afferents -- reticular formation & limbic system.
  • Efferents -- cortical connections & basal ganglia
  • Functions as a diffuse thalamic activation system.
    • Produces cortical desynchronization.
    • Critical for perception of stimuli.
    • Decreased activity during sleep.

Paleothalamus:

Preliminary processing of sensory information to cortex.

Two way connections

Neothalamus:

• Largest division of nuclei
• Projects to association areas of the cortex.
• Larger in animals with well-developed cortex.
• Intrinsic nuclei -- input from other thalamic nuclei.

Archithalamus

Description

• Oldest division of thalamus; animals with rudimentary cortex; sense of smell.
• Functions as a diffuse thalamic activation system
• Produces cortical desynchronization
• Critical for perception of stimuli
• Decreased activity during sleep
• Afferents and Efferents
  • Afferents-- reticular formation & limbic system
  • Efferents--cortical connections & basal ganglia

Archithalamic Nucleus:

• Internal medullary lamina - divides medial and lateral segments

Archithalamus has midline connections with:

• Hypothalamus, basal ganglia, amygdala, orbital gyri (diffuse fibers to association cortex)

• Intralaminar (in internal medullary lamina)
  • Largest (centrum medianum)
  • Receives diffuse spinal and RF connections
  • Diffuse cortical projections
• Reticular - lateral to external medullary lamina
  • Diffuse efferent system to cortex

• Anteroventral nucleus -- from mammilothalamic tract to cingulate gyrus

Paleothalamus

Description

• Preliminary processing of sensory information to cortex; two-way cortical connections

Paleothalamic Nuclei:

1. Lateral Geniculate
   • project to area 17
   • Primary Vision pathway
   • Largest ganglion cell axons

2. Medial Geniculate
   • Projects to middle 1/3 of superior temporal gyrus
   • Audition

3. Posterior Ventral lateral nucleus
   • Fibers from Medial Lemniscus
   • all somatosensory pathways
   • Project to post central gyrus

Neothalamus

Description

• Largest division of nuclei
• Projects to association areas of cortex
• Larger in animals with well-developed cortex
• Intrinsic nuclei--input from thalamus

Neothalamic Nuclei:

1. Medial nucleus--projects frontal cortex (non-motor)
   • Afferents--from ventral nuclei, hypothalamus
   • Dorsal lateral nucleus & posterior lateral -- parietal projection nuclei

2. Nucleus lateral posterior--parietal and temporal
   • Temporal pole area has no thalamic connections
   • Receives medial geniculate connections
   • Projects to audio-psychic zone of temporal lobe

3. Nucleus lateralis dorsalis
   • Afferents--somatic sensory nerves
   • Efferent--area 7 of parietal lobe

4. Pulvinar
   • Afferent--lateral and medial geniculate bodies
   • Two-way connection with visuopsychic area

5. Ventral anterior nucleus
   • From globus pallidus to limbic areas and back

Functions of the Thalamus

• Thalamus and cortex have area-to-area connections
• These connections are usually two-way
• If the thalamus were only a relay, it would be an inconvenient relic
• Transmission of sensory message does not concern the neothalamus
• May play role as a level of sensory integration
• Attention

Terms to Know