Limbic Thalamic Nuclei Size

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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. Nuclei that interconnect heavily with the limbic system include the anterior thalamic nuclei and lateral dorsal nucleus, which have dense connections with the hippocampus (a structure critical for forming new episodic memories) and with cingulate cortex (an area of cortex which has many functions).

The anterior thalamic nuclei generally scale with negative allometry (i.e. they become proportionally smaller in larger brains) in anthropoid primates. While the human anterior thalamic nuclei follow this pattern, the density of neurons in these nuclei decrease less than expected. This results in a larger total number of neurons than expected in human limbic thalamic nuclei, among the largest increases of thalamic nuclei observed.

The functional significance of these nuclei is unknown.  These differences may be related to human-specific changes in the hippocampus, amygdala, or prefrontal cortex, and related to social and memory functions.


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
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