Vertebrate brain theory

ISBN 978-3-00-064888-5

Monograph of Dr. rer. nat. Andreas Heinrich Malczan

7         The further development of the Pontocerebellum

7.1        The integration of limbic signals into the cerebellum system

In the course of the evolutionary development of the cerebellum, limbic signals were also integrated into the cerebellum system. The first step was the development of the limbic signaling pathway via the dopaminergic area tegmentalis ventralis (VTA), which was used to generate time-delayed signals. On the other hand, the basal ganglia system also used the dopaminergic signaling pathway for the elementary signals and the mean value signals. And especially the striatum with the globus pallidus served the cerebellum as signal source for the climbing fibers.

Over time, this signaling pathway has been used for the limbic system. One reason may be the use of the common transmitter dopamine. The limbic signals already went to the VTA, which initially only projected back to the limbic system, probably mainly to the amygdala. The limbic, or more precisely the olfactory system, was one of the first in the course of evolution. One could well imagine the formation of the dopaminergic substantia nigra pars compacta as an offshoot of VTA. Over time, this dopaminergic offshoot system took over the processing of motor and sensory signals. And its primary target was the striatum.

It can therefore be assumed that the striatum was also capable of taking up limbic signals from the dopaminergic region of origin of VTA. Initially, motor and sensory functions were quite elementary, so that there were not many signals to process. Apparently, a topological separation already existed at that time, so that the olfactory signals in the developing striatum were spatially separated from the motor and sensory signals. Thus, an olfactory/limbic striatum developed ventrally from the motor striatum. This neuron nucleus is today called nucleus accumbens or ventral striatum.

According to the author's theory, the ventral striatum generates the limbic climbing fiber signals for the cerebellum. However, at least at a sufficient level of evolution, most of the limbic signals were maximum coded and represented clocked and tetanic oscillations. Here, no signal transformation was required. The limbic climbing fibre signals were therefore particularly suitable for embossing. The only thing missing was access to limbic signals via the parallel fiber system. For this purpose, the limbic cortex regions had to project into the cerebellum via the bridge cores. Then, for each active limbic signal a separate Purkinj group could be imprinted, which was later activated via the climbing fiber when this signal was active. The output of the cerebellar nucleus reached the cortex and found its way back to the cerebellum via the bridge nuclei. There the limbic signals could be combined with non-limbic signals and used to imprint new complex signals. Thus, the cerebellum does not serve as an inversion system for the maximum coded limbic signals, but already as a neuronal network with climbing fiber imprinting.

Monograph of Dr. rer. nat. Andreas Heinrich Malczan