The paleothalamus is an obsolete term for the portion of the

thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...

that is believed to be

phylogenetically In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

(or

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

arily) older than other parts of the thalamus. Specifically, the midline and medial nuclei of the thalamus, as well as the intralaminar nucleus, are considered to belong to the paleothalamus The term "paleothalamus" is opposed to the paired term neothalamus (also considered to be obsolete), which designates the phylogenetically (or evolutionarily) newer or younger parts of the thalamus, specifically, lateral nuclei of the thalamus, the pulvinar and the geniculate bodies. Initially, the paleothalamus was distinguished from other parts of the thalamus (i.e. from the neothalamus) on the basis that paleothalamic nuclei were believed to lack reciprocal connections with

neocortex The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, ...

( isocortex), unlike neothalamic nuclei, which have manifold reciprocal connections to the neocortex. Today it is known that thalamic nuclei which were previously termed "paleothalamic" also have such reciprocal connections with neocortex. This was the main reason why the terms "paleothalamus" and "neothalamus" were felt obsolete and fell into disfavor.

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Thalamus {{neuroanatomy-stub