Why is the thalamic reticular nucleus called a nucleus? In the Wikipedia article on nuclei) I read: > A nucleus is one of the two most common forms of nerve cell organization, the other being layered structures. Is there a specific and plausible reason, why the thalamic reticular nucleus is called a nucleus, even though it is - anatomically - a layer? Has the TRN once been a somehow spherical nucleus and evolved into a two-dimensional layer? Or does the TRN play a functional role that normally nuclei play, but not layers?

The thalamic reticular nucleus (TRN) is a thin layer of GABAergic cells adjacent to the thalamus (Fig. 1). Because of its strategic location between the thalamus and cortex, the TRN is often suggested to be important to attention and regulation of information flow between the thalamus and cortex (Lam & Sherman, 2011).

A **nucleus** is defined as a

> [p]ortion of tissue that are compact accumulations of neurons having roughly similar connections and functions

**Reticular** is defined as

> **A fine network or net-like structure**.

So reticular nucleus translates itself as a **net-like accumulation of neurons**.

In contrast to the wikipedia meaning, therefore, I interpret _nucleus_ as more of a **cluster of functional organizational units** rather than a _morphological characteristic_ of that cluster _per se_.

![TRN](
Fig. 1. Thalamic reticular nucleus. source: Dana Foundation

**Reference**
**-** Lam & Sherman, _J Neurosci_ (2011); **31** (18): 6791-9