Vertebrate brain theory

4.7   The hyperpallium of birds - a convergence system and a vertical convergence grid

In birds, the output of the spinocerebellum, which increased extremely in number due to the signal divergence in the nucleus olivaris, did not only remain inside the cranial turning loop in order to be processed by the neurons of the dorsal ventricular ridge (DVR).

When the number of signals had reached a certain threshold, there was no more room in the ventricle space. The DVR had displaced the ventricular fluid to the maximum and took its place. Further growth had become impossible.

For reptiles this meant the end of a further spiritual development. But for birds it meant the end of a further spiritual development.

It seems that in birds, the axons with the other cerebellar signals found a way to the outer surface of the brain, thus creating a kind of new turning loop. In contrast to the frontal cortex of mammals, however, this was not a horizontal convergence grid, but was vertically oriented, just like the DVR. Thus, this turning loop was a vertical convergence lattice and had virtually the same cytoarchitectonic structure as the DVR in the ventricular space of reptiles and birds. Today it is called hyperpallium. However, this only concerns the areas that received the output of the spinocerebellum after the formation of the signal divergence. The remaining areas of the cortical turning loops - which in mammals form the temporal lobe, the parietal lobe and the occipital lobe - probably developed into vertical divergence grids on the sensory side in birds, while the motor side represented a vertical convergence grid. This monograph is not intended to say more; this problem could be the subject of a separate monograph.

Regardless of whether the DVR, hyperpallium or motor frontal cortex was a horizontal or vertical convergence grating, the further signal processing remained more or less the same. The output was fed to the basal ganglion system, the cerebellum (more precisely the pontocerebellum) and the motor system of the spinal cord. This will be described in more detail later for mammals, but the principle of signal processing remained the same. The basal ganglions provided the signals for the generation of a time-sensitive differential image for motion detection. The pontocerebellum was used to bind elementary signals to complex signals and the spinal output was used for motor control depending on the result of signal superposition in the association areas.

Theorem of the hyperpallium as convergence lattice

The hyperpallium of birds is a vertical convergence grid, which corresponds to the frontal cortex of mammals in its mode of operation, but is not oriented horizontally in the plane, but vertically in space. It reverses the signal divergence of the nucleus olivaris so that the output can be used for motor control.