notes-science-neuro-thalamus

Evolution / comparative

mice and rats seem to lack dorsal thalamic interneurons, but other mammals have them

"Features shared by the dorsal thalamus of reptiles and that of mammals include projection to the telencephalon, specific and non-specific non-telencephalic afferents, and input from the thalamic reticular nucleus. Differences between the dorsal thalamus of reptiles and that of mammals are the absence of reciprocal telencephalic efferents to the dorsal thalamus and lack of local circuit neurons in reptiles (with the exception of the dorsal geniculate complex in turtles) and their presence in mammals. A thalamic reticular nucleus is present in both reptiles and mammals. In both of these classes of vertebrates, this neuronal aggregate surrounds the dorsal thalamus along its lateral surface, projects to the dorsal thalamus, and is organized into sectors" -- http://www.ncbi.nlm.nih.gov/pubmed/8564463 (abstract) The thalamus of reptiles and mammals: similarities and differences

" For many years it was thought that the olfactory pathway also passes through the thalamus, from olfac- tory cortex through the mediodorsal thalamic nucleus to prefrontal cortex. However, recent careful anatomical studies have shown that the pathway between olfac- tory cortex and prefrontal cortex is mostly direct, with only a small contingent of fibers going to mediodorsal thalamus ( Ongur and Price, 2000 ). Within prefrontal cor- tex, the primary olfactory area consists of the medial and lateral orbitofrontal cortex. " -- http://www.cell.com/neuron/retrieve/pii/S0896627305002333 Perception without a Thalamus, Shepherd

The Shepherd article also notes tht the olfactory cortex has sleep states synchronized with neocortex.

http://www.ncbi.nlm.nih.gov/pubmed/17161473 "An argument for an olfactory thalamus" details many similarities between the olfactory bulb and the thalamus

sherman and guillery chapter 2 fig 2.8 and corresponding text gives the strong impression that although each species has an orderly specification of cell type x ipsilaterality to layers, this not preserved across species. This reminds me of the evidence that avians have a cortex homology that has gone unrecognized because it has no layers; and http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2951601/ Specificity and randomness in the visual cortex Kenichi Ohki, M.D., Ph.D. and R. Clay Reid, M.D., Ph.D. and Chklovskii's work about the salt-and-pepper arrangement of rodent visual cortex orientation maps vs the ordered arrangement of primate visual cortex orientation maps. The general picture seems to be that strikingly orderly maps are often species-specific and that other species often manage similiar connectivity with similiar function without precise spatial order. This suggests that the researcher interested in general principals of brain architecture should not spend much time on the details of strikingly orderly maps without first confirming them in multiple taxonomic orders, except insofar as they suggest semantic dimensions of the local topology of connectivity (for example "orientation") which may be generic but difficult to observe in other species.