Relation
- Lies below the posterior part of the thalamus
- Lies behind and lateral to the hypothalamus.
- Inferiorly, the ventral thalamus is continuous with the tegmentum of the midbrain.
- Laterally, it is related to the lowest part of the internal capsule.
Formed by two masses of grey matter
Fibre Bundles Passing Through Subthalamic Region
- Many long tracks pass through this region
- Fields of Forel (H, H1, and H2): term fields of Forel is used to designate a dense mesh of fiber bundles that lie within the subthalamus rostral to the midbrain.
- H Prerubral field
- Consist of
- Ascending tracts (medial lemniscus, spinal lemniscus, trigeminal lemniscus) pass through it on their way from the midbrain to the thalamus.
- Dentatothalamic
- Rubrothalamic fibres
- Ansa lenticularis
- Part of substantia innominata
- Connect the globus pallidus → thalamus.
- Course
- Starting from the globus pallidus, the ansa lenticularis winds round the ventral and posterior border of the internal capsule to reach the subthalamic region,
- Relations
- Lies ventral and medial to the subthalamic nucleus.
- H2 (Fasciculus lenticularis) - see below
- Nuclei of the prerubral field:
- Consist of Some neurons lying along the lower edge of the zona incerta (near the upper end of the red nucleus).
- H1 Thalamic field
- At a location medial to the subthalamic nucleus
- Consist of:
- Ansa lenticularis fibres
- Fasciculus lenticularis fibres
- Rubrothalamic fibres
- H2 (Fasciculus lenticularis)
- Connect the globus pallidus → thalamus.
- Fibres of the fasciculus lenticularis intersect those of the internal capsule to reach the subthalamic region. Here, they pass medially above the subthalamic nucleus and below the zona incerta.
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