= Epithalamus
The \b[epithalamus] is a dorsal posterior subdivision of the <diencephalon>, associated with the roof of the <third ventricle>. Its usual anatomical scope includes the <habenula> and associated fiber systems, the <pineal gland> and the epithelial ventricular roof. It is a region containing distinct structures, not merely another name for the pineal gland.<Epithalamus in NLM MeSH>[Scope note: dorsal posterior position and usual components; classification convention for paraventricular thalamic nuclei.]{ref}
One component supplies an experimentally clear example. <Masayuki Matsumoto> and <Okihide Hikosaka> recorded from the <lateral habenula> during a reward-associated eye-movement task in rhesus monkeys. Many neurons increased activity for an unrewarded target and decreased activity for a rewarded target, while recorded dopamine-neuron responses showed the opposite pattern.<Lateral habenula as a source of negative reward signals in dopamine neurons by Masayuki Matsumoto and Okihide Hikosaka>[2007 abstract: visually guided task and opposite reward-related response signs.]{ref}
Reversing which target location earned reward also reversed the responses. This is an illuminating control: a response following the reward assignment is harder to explain as a fixed preference for one screen position. Habenular excitation preceded dopamine-neuron inhibition on unrewarded trials, and weak electrical stimulation of the <lateral habenula> inhibited dopamine neurons.<Lateral habenula as a source of negative reward signals in dopamine neurons by Masayuki Matsumoto and Okihide Hikosaka>[Reward-location reversal, temporal order and stimulation results.]{ref}
Recording and intervention provide different evidence. Opposite responses and timing motivate a circuit hypothesis; stimulation tests influence on another population. Neither establishes that every epithalamic structure performs reward evaluation, nor that the influence is necessarily a direct monosynaptic inhibitory connection. Anatomical membership should not be confused with uniform physiological function.
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