Non-laminar cerebral cortex in teleost fishes?

Abstract

A large skull is disadvantageous to animals that move quickly in three-dimensional space, such as fishes and birds in water or air. A cerebral neocortex with a six-layered sheet has not evolved, most likely due to the limited cranial space. Instead of the laminar cortex, telencephalic nuclear masses seem to have evolved as the pallium in teleost fishes. We consider that the nuclear masses contain rather simple neural circuits sharing a skeleton of simple circuits in the mammalian cortex, which have been elaborated by additional circuits in mammals. Such basic similarities at the connectional level shared by nuclear and cortical pallium might underlie similar or equivalent functions.

Vertebrate brains and evolutionary connectomics: on the origins of the mammalian ‘neocortex’

“…These convey auditory and electrosensory information from the periphery to various regions within the 'dorsal ridge' of the teleost brain, with striking resemblances to corresponding pathways in mammals and birds. Yamamoto et al [37] and Maler et al [38] rstb.royalsocietypublishing.org Phil. Trans.…”

How do individuals cope with stress? Behavioural, physiological and neuronal differences between proactive and reactive coping styles in fish

“…Instead, teleostean telencephalic pallial areas contain aggregates of neurons (Ito and Yamamoto, 2009), similar to those of birds (Karten, 1991;Shimizu, 2007). Interestingly, the lack of a 6-layered pallium does not imply an absence of so-called 'higher functions', and telencephalic cortical-like functions have been reported in several fish species (Bshary and Brown, 2014;Demski, 1983;Grosenick et al, 2007;Ito et al, 2007;Ocaña et al, 2015).…”

Evolution of the forebrain — revisiting the pallium

“…One hypothesis considers the lateral part to be homologous to the hippocampus while the medial part would represent the claustroamygdaloid complex (Northcutt, 2006). A contravening hypothesis considers both the lateral and medial sensory recipient zones to be homologous to components of the neocortex, and perhaps only to its layer IV (Yamamoto et al, 2007;Ito and Yamamoto, 2009). These two sensory recipient zones in teleosts might arise from a common embryonic progenitor pool, as proposed by Jarvis et al for separated pallial fields Figure 1.…”