Sensory Thalamic Nuclei Size

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True   Likely   Speculative
Human Uniqueness Compared to "Great Apes": 
Relative Difference
Human Universality: 
Individual Universal (All Individuals Everywhere)
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The thalamus is a neural structure found in all vertebrates, located at the dorsal end (top) of the brain stem. It consists of 30 to 40 “nuclei”, or interconnected groups of neurons. “Association” nuclei include the pulvinar nuclei, the lateral dorsal nucleus (LD; also known as the “visual pulvinar”), and the dorsomedial nucleus. The pulvinar is itself a conglomerate of 6-8 nuclei, and is associated with connections to higher-order visual and auditory cortex.

The total volume of the pulvinar and LD together shows positive allometry; the combined volume fits within expectations for an ape with a large brain. Individually, the pulvinar is slightly larger, and the LD slightly smaller, than expected. The pulvinar has about twice as many neurons as the great ape pulivinar, while the number of neurons in the human LD is not significantly different than that of gorillas (the only great ape measured) (Armstrong, 1981).  The dorsomedial nucleus, which has heavy connectivity to frontal cortex, also shows more neurons than expected.

Besides these differences, the pulvinar (along with other dorsal thalamic nuclei), attracts migrating GABA-ergic interneurons during development (Letinic & Racic, 2001). This developmental pattern has not been observed in any other primates, including the great apes (Sherwood et al, 2008).  The migratory pattern of GABA-ergic interneurons to the dorsal thalamus is believed to be unique to humans, and has also been suggested to contribute to higher-order functions as well (Sherwood et al, 2008). This is consistent with the view that most of the thalamus plays a critical role in cortico-cortico communication (Sherman, 2007), and as a hub for attentional modulation and other global brain states, such as sleep (McCormick, 1991; Steriade, 2001).

It has been suggested that sub-nuclei of the pulvinar may have differentially expanded/contracted during human evolution, due to specializations in higher-order functions of humans (Armstrong, 1981). This is supported by the fact that the “pars inferior” aspect of the pulvinar, which has well-described visual functions shared with other great apes, does not show the increased allometry that the rest of the pulvinar does (Armstrong, 1981).  In addition, left (and not right) pulvinar has been associated with some language-related functions, such as naming and verbal memory (Johnson and Ojemann, 2000).


Timing

Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Possible Appearance: 
6,000 thousand years ago
Definite Appearance: 
100 thousand years ago
Occurrence in Other Animals: 

The pulvinar and LP are considerably different between prosimians and anthropoid primates (Wong et al, 2009), suggesting an early origin of the basic structure of the human pulvinar.

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Referenced By:
Title Certainty
Limbic Thalamic Nuclei Size Speculative
Motor Thalamic Nuclei Size Speculative
Size of Sensory Thalamic Nuclei Speculative

References

  1. Cortical connections of the visual pulvinar complex in prosimian galagos (Otolemur garnetti)., Wong, P., Collins C. E., Baldwin M. K. L., and Kaas J. H. , J Comp Neurol, 12/2009, Volume 517, Issue 4, p.493-511, (2009)
  2. A natural history of the human mind: tracing evolutionary changes in brain and cognition., Sherwood, C. C., Subiaul F., and Zawidzki T. W. , J Anat, 04/2008, Volume 212, Issue 4, p.426-54, (2008)
  3. The thalamus is more than just a relay., S Sherman, Murray , Curr Opin Neurobiol, 2007 Aug, Volume 17, Issue 4, p.417-22, (2007)
  4. Telencephalic origin of human thalamic GABAergic neurons., Letinic, K, and Rakic P , Nat Neurosci, 09/2001, Volume 4, Issue 9, p.931-6, (2001)
  5. Thalamus, Steriade, M. , eLS, (2001)
  6. The role of the human thalamus in language and memory: evidence from electrophysiological studies., Johnson, M D., and Ojemann G A. , Brain Cogn, 03/2000, Volume 42, Issue 2, p.218-30, (2000)