Limbic Thalamic Nuclei Size

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.