The article "Habenula" by Okihide Hikosaka is very interesting. It is a very well written short overview of the place and role of the habenula in the brain, complemented with outstanding recently published data (Matsumoto and Hikosaka).
I just have very minor concerns. I will go from top to bottom.
1) First paragraph: line 10. I would put "a" before "phylogenetically".
2) "Outputs" paragraph. I would add "," after "located" (line 4).
3) "Function of medial habenula" paragraph: I would put a "as" after "acting" (line 10).
4) "Function of medial habenula" paragraph: I would re-phrase the sentence line 9 as follow: "Interleukin-18, which is a pro-inflammatory cytokine acting as a modulator of immune functions, is localized in the brain in the interpeduncular nucleus, ependymal cells and also in the medial habenula where restraint stress increases its release (Sugama et al., 2002)."
5) "Cognitive function" paragraph. (line 8) rather than the "Lecourtier et al. (2006)" reference I would put the references of the original articles that showed in the hippocampus increased noradrenaline (Kalen et al., 1989) and acetylcholine (Nilsson et al., 1990) release after habenular stimulation.
6) "Dysfunctions of habenula: implication in psychosis" paragraph: I would add the reference by Caputo et al. (1998) to strengthen the point about calcification of the habenula and schizophrenia.
Caputo A, Ghiringhelli L, Dieci M, Giobbio GM, Tenconi F, Ferrari L, Gimosti E, Prato K, Vita A. Epithalamus calcifications in schizophrenia. Eur Arch Psychiatry Clin Neurosci. 1998;248(6):272-6.
Kalén P, Lindvall O, Björklund A. Electrical stimulation of the lateral habenula increases hippocampal noradrenaline release as monitored by in vivo microdialysis. Exp Brain Res. 1989;76(1):239-45.
Nilsson OG, Kalén P, Rosengren E, Björklund A. Acetylcholine release in the rat hippocampus as studied by microdialysis is dependent on axonal impulse flow and increases during behavioural activation. Neuroscience. 1990;36(2):325-38.
User 2: This page needs more pictures!
It would be great to see more images of the habenula. Three-dimensional models always work wonders.