Size of Dentate Nucleus

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Human Uniqueness Compared to "Great Apes": 
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The dentate nucleus is relatively larger in humans than in other primates.  Much like the cerebrum, the cerebellum consists of cortical gray matter overlying white matter within which lie subcortical nuclei, known as cerebellar deep nuclei. The dentate nucleus is the most lateral of these three nuclei and is distinctive in sending output to the cerebral cortex. The dentate nucleus is part of a loop linking the cerebellum with the cerebral cortex, in which information flows from cerebral cortex to lateral cerebellar cortex by way of the pons, to the dentate nucleus, to thalamus, and then back to cerebral cortex. The dentate nucleus becomes increasingly convoluted in moving from prosimians to monkeys to apes to humans. A larger surface area may allow for a greater number of synapses from purkinje cell axons from cerebellar cortex. On the basis of morphological, histological, embryological, histochemical, and pathological evidence, the dentate nucleus is thought to consist of two parts: a dorsomedial and a ventrolateral part. It has been suggested that the ventrolateral part is unique to humans and apes. Humans have a larger dentate nucleus for their body size than apes, suggesting greater cerebellar output to the cerebral cortex, and this difference is concentrated in the ventrolateral portion of the nucleus that is hypothesized to send output to non-motor regions of the frontal lobe by way of the ventrolateral thalamus. This would imply greater cerebellar involvement in cognition in humans compared with apes. Further evidence of specialization of the human dentate nucleus is provided by the observation that the relative size of the dentate nucleus compared with the other two deep nuclei is most divergent in humans, suggesting that a larger proportion of cerebellar output reaches the cerebral cortex in humans. 

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

Definite Appearance: 
100 thousand years ago
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Size of Sensory Thalamic Nuclei Speculative

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