The hippocampus of birds in a view of evolutionary connectomics

The avian brain displays a different brain architecture compared to mammals. This has ledthe first pioneers of comparative neuroanatomy to wrong conclusions about bird brainevolution by assuming that the avian telencephalon is a hypertrophied striatum. Based ongrowing evidence from divers analysis demonstrating that most of the avian forebrain ispallial in nature, this view has substantially changed during the past decades. Further, birdsshow cognitive abilities comparable to or even exceeding those of some mammals, evenwithout a “six-layered” cortex. Beside higher associative regions, most of these cognitivefunctions include the processing of information in the hippocampal formation (HF) thatshares a homologue structure in birds and mammals. Here we show with 3D polarized lightimaging (3D-PLI) that the HF of pigeons like the mammalian HF shows regional specializationsalong the anterioreposterior axis in connectivity. In addition, different levels of adultneurogenesis were observed in the subdivisions of the HF per se and in the most caudalregions pointing towards a functional specialization along the anterioreposterior axis.Taken together our results point to species specific morphologies but still conservedhippocampal characteristics of connectivity, cells and adult neurogenesis if compared to themammalian situation. Here our data provides new aspects for the ongoing discussion onhippocampal evolution and mind