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Joined 2026-09-21 Message
Incoming links: Telencephalon
Forebrain 2026-11-05
The forebrain, also called the prosencephalon in embryological terminology, is the anterior major division of the developing vertebrate brain. It subdivides into the telencephalon and diencephalon. The name describes a developmental and anatomical grouping, rather than one nucleus with a single task.[ref]
Prosencephalon in NLM MeSH. Scope note and Forebrain entry term: anterior primitive cerebral vesicle derived from the neural tube and its two subdivisions.
The telencephalon includes the cerebral-hemisphere system, while the diencephalon includes regions such as the thalamus, hypothalamus and epithalamus. Thus the visible cerebral cortex is part of the forebrain but does not exhaust it. Deep nuclei and connecting pathways also belong to the region.[ref]
Neuroscience, 2nd edition edited by D. Purves and others. Gross organization of the brain and ventricular-system anatomical landmarks.
The ventricular spaces provide an illuminating map. The lateral ventricles lie within the cerebral hemispheres, while the third ventricle is associated with the diencephalic region. A fluid-filled cavity and its surrounding neural tissue are different structures: locating the cavity helps orient the tissue, but does not make the cavity itself a neuron-processing center.[ref]
This developmental grouping is useful when comparing brains whose proportions differ greatly. Expansion of one forebrain component does not erase the distinction among its components. Likewise, observing a response in the lateral habenula identifies activity in one forebrain circuit, not a computation performed uniformly by the entire forebrain.
Telencephalon 2026-11-05
The telencephalon is the anterior subdivision of the embryonic forebrain and the corresponding territory of the mature brain. Its derivatives include the cerebral hemispheres, with cerebral cortex, deeper basal ganglia and associated structures, including the olfactory bulbs. It is an anatomical and developmental division, rather than a name for one behavior or one type of neuron.[ref]
Telencephalon in NLM MeSH. D013687 scope note and anatomy hierarchy: anterior prosencephalic subdivision; cerebral and associated structures.
The forebrain divides into telencephalon and diencephalon. These names should not be treated as interchangeable: the thalamus belongs to the diencephalon, whereas cerebral cortex belongs to the telencephalon. The large cerebral hemispheres can cover deeper regions in a surface view, so apparent position in a photograph alone is a poor guide to developmental membership.[ref]
Prosencephalon in NLM MeSH. D016548 scope note: subdivision into diencephalon and telencephalon.
A practical example is classifying structures in a section through the brain. A region of cerebral cortex and a deep basal ganglia nucleus can both be telencephalic even though one is superficial and the other deep. Conversely, an adjacent thalamus is diencephalic. This distinction makes the telencephalon useful as a map of related structures without assuming that everything within that map performs the same computation.