Zinc-positive and zinc-negative connections of the claustrum

Three features often mentioned as characteristic of the claustrum are its widespread connections with cortical areas, the reciprocity of these connections in general, and the origin of cortico-claustral connections from a distinctive subtype of layer 6 pyramidal cells (Sherk, 1986; Katz, 1987; Tanne-Gariepy et al., 2002; Crick and Koch, 2005; Smythies et al., 2012). Another feature, often overlooked, is that a proportion of claustral-cortical neurons use synaptic zinc and that zinc+ terminations are moderately dense in the claustrum. This article will summarize data about zinc and the claustrum and present the case that cortico-claustral neurons might also be zinc-positive (Zn+). I conclude with comments on the likely implications for claustral identity and function.