Claustrum is a thin, curved and wavy sheet of gray matter which is well demonstrated in cross section of cerebrum. It is situated lateral to lentiform nucleus from which it is separated by external capsule. Laterally claustrum is related to insular cortex, but separated by extreme capsule. Developmentally, claustrum is a component of archistriatum. Connections and functions of claustrum are not known.

Connections of corpus striatum
Fundamentals of connections of corpus striatum are to be understood first. Neostriatum (caudate nucleus and putamen) receive inputs from various parts of central nervous system. Informations are thenintegrated. Next, directives are sent to palleostriatum (globus pallidus) which sends output.
Afferent fibers (to neostriatum):

  1. Corticostriate fibers: Fibers from each part of motor as well as sensory areas of cerebral cortex project to a specific part of caudate-putamen complex. The fibers are mostly ipsilateral. Maximum number of inputs are from motor and sensory cortex. Neurotransmitter is glutamate.
  2. Thalamostriate fibers: These fibers originate from intralaminar nuclei of thalamus.
  3. Nigrostriate fibers: Neurons of substantia nigra send axons which end in caudate nucleus and putamen to release dopamine which is inhibitory in function.
  4. Ascending fibers from brainstem and spinal cord: From different centers of brainstem otherthan substantia nigra, fibers ascend to neostriatum to liberate serotonin which is also inhibitory in function. Similar functional fibers also ascend from spinal cord.

Interconnecting fibers (Striopallidal fibers): These fibers pass from neostriatum (caudate nucleus and putamen) to pallidum (globus pallidus). Neurotransmitter released by these fibers are Gamma-aminobutyric acid (GABA). Some of the fibers from caudate nucleus – putamen complex pass back to substantia nigra. Neurotransmitters released from these fibers are GABA or acetylcholine.
Efferent fibers (Pallidofugal fibers):
After the informations (inputs) from different centers of central nervous system are received and integrated in corpus striatum (caudate nucleus and putamen), these are channelled to globus pallidus. Globus pallidus then influences activities of motor areas of cerebral cortex and other motor centers in brainstem. Globus pallidus influence directly to brainstem centers. But cerebral cortex, so also spinal cord are influenced indirectly through thalamus. So direct pallidofugal fibers are to:
  1. Thalamus
  2. Subthalamus
  3. Brainstem tegmental centers.

These pallidofugal fiber are as follows:
  • Ansalenticularis : These pallidofugal fibers loop around posterior limb of internal capsule to reach ventroanterior and ventrolateral nuclei of thalamus.
  • Fasciculus lenticularis: These fibers also reach the same nuclei of thalamus, but traversing through posterior limb of internal capsule.
  • Subthalamic fasciculus: These pallidofugal fibers connect subthalamic nucleus in both directions. Subthalamic nucleus is a small mass of gray matter which presents biconvex appearance in coronal section. It is located caudal to thalamus and inferomedial to globus pallidus from which it is separated by fibers of internal capsule. Subthalamic fasciculus connect globus pallidus with subthalamic nucleus in both directions. The fibers of the fasciculus traverse internal capsule.
  • Pallidotegmental fibers: These fibers descend from globus pallidus to motor centers situated in tegmentum of brainstem.

Source: Easy and Interesting Approach to Human Neuroanatomy (Clinically Oriented) (2014)