ISBN 978-3-00-068559-0
Monograph of Dr. rer. nat. Andreas Heinrich Malczan
A brain theory should be verifiable to some extent. Verification is sometimes difficult. When a theory is put forward about consciousness or the origin of thoughts, verification can be problematic. This is because thoughts in themselves are not a material sub-state that can be verified.
Therefore, it seems appropriate to the author to make the verification of his brain theory possible under the aspect of motor skills. To this end, we will present the most important aspects of this brain theory and the various sub-stages of brain development using motor function as an example. The aim is to relate real cytoarchitectonic structures to the generation of movements. Here, everyone can check the results if they have sufficient neuronal and mathematical knowledge. We will analyse the generation of directed movements by two basic structures of the vertebrate brain. On the one hand, the torus semicircularis serves to generate movements. On the other hand, directed movements are also caused by the tectum opticum. And finally, in higher mammals, movements are also controlled cortically.
Before we start analysing the torus and tectum, let us hypothetically enumerate the developmental steps that the vertebrate brain underwent in the course of evolution as it evolved from the original rope ladder nervous system.
Stage 1: Separation of modalities
Already in the unsegmented multicellular organism, a separation of modalities began. There were sensory modalities, motor modalities and mean modalities. Therefore, there were three types of neuronal centres in the Bilateria, whose lineages led to the vertebrates: one sensory centre per body half, one motor centre per body half and probably several mean value centres per body half. The latter served to control the life support systems.
This was not only a separation of the modalities according to sensory motor and mean control, but also a separation according to body sides.
In the resulting segmented bilateria with rope ladder nervous system, a separation of modalities by segments was added. In addition, the neurons separated into neuronal layers that contained only neurons of one modality. The number of layers of different modalities increased with the number of different types of receptors. At a certain stage of development, the modalities in the upper head layers of the rope ladder system separated into separate sub-ladders from which the brain lobes emerged. The separation or splitting of the modalities progressed further, and separate nerve tracts for different modalities even developed in the spinal cord. In the brainstem, the separation of modalities led to the emergence of specific nuclei that had to perform only partial tasks in the system (e.g. ocular nuclei, vestibular nuclei, auditory nuclei, torus semicircularis, tectum opticum, etc.).
Stage 2: Provision of inverted signals
In the input and output floor of the cord ladder nervous system, the cerebellum formed, which was capable of inverting signals.
The inverted signals of the cerebellum were classified as independent modalities and formed independent modal layers in the structures of the brain.
For motor control, the development of inverted signals meant a significant advance; now muscles and their motor counterparts could be tensed simultaneously, which could compensate for the effect of gravity.
Stage 3: Nucleation of the modality layers
In the early developmental epochs of vertebrates, the modality layers were arranged in a cylinder, corresponding to the shape of the neural tube. Here, sensory and motor signals were each assigned to one half of the cylinder.
In the upper segments of the neural tube, the central canal of the ventricular space narrowed, and at the same time a transition took place in the upper segments from the cylindrical organisational structure of the modality layers to approximately circular modality layers, which were now simply stacked on top of each other. An intermediate stage could be seen as a form of organisation in which the modalities were arranged in half-shells, similar to the cortex, in which this variant was retained. The deeper segments of the cephalic tiers formed more approximately circular modality layers, similar to the corpus geniculatum laterale in humans. This was possible because the ventricular space completely disappeared from these originally tube-like structures near the head and now - in humans - only remained below these structures. Above the ventricular wall, for example, are the thalamic structures. The ventricular system did not disappear, however, but partly shifted to the lateral parts formed by the two brain hemispheres.
The stacking of the layers now also referred to the segments, which now also formed round segment stacks, which we interpret as nuclei, also called cores
As different modalities simultaneously split and formed separate, more rounded axon bundles, there were separate nuclei or nuclei for each independent modality.
In each nucleus, the neurons were arranged in roundish layers, with each layer representing a body segment. The layered structure of the nuclei thus also reflected the body structure according to segments.
Since the sensory system predominantly served the motor system, the signals that were provided by the motor system as sensory control variables of the motor system, e.g. the signals of the muscle spindles or the tendon organs, were also available in many sensory nuclei. Thus, in the nucleus that received the vestibular signals, there were simultaneously all the signals of those muscle groups that caused body movements in response to these signals.
Stage 4: Formation of mutually inverse double layers
Many nuclei received the return input from the cerebellum in addition to the input from the associated receptors. This is because the receptor input also reached the nucleus ruber in a descending manner, changed sides via the nucleus olivaris and became the cerebellum input. The cerebellum inverted these signals and sent them
headwards after the side change to the original side, so that they reached the original core again and formed their own input layer there with inverted signals.
The nucleus thus contained a double layer of mutually inverse signals. Between the two input layers there was now an output layer of output neurons. To differentiate, we call the input layer with the original signals from the receptors the primordial layer, and the layer with the inverted signals the inverse layer. The primordial layer was evolutionarily older and usually formed the lower layer (tailward), the inverse layer was above it (headward). Mostly, the neurons of the input layer and the output layer belong to neuron class 4.
In the modalities that produced receptor types with mutually inverse signals, as was the case with visual signals, the inverse signals did not need to be formed by the cerebellum. Here, the signal origin differed. A stratification of the visual nuclei according to ON-modalities and Off-modalities nevertheless remained as if the Off-modalities had been formed by the cerebellum.
Stage 4: Occurrence of signal divergence in depth
In the beginning, there was an output shift for every input shift. The goals were mostly motoric.
With the formation of the inverse double layers, there was also a doubling of the output layers. The on-layer supplied the on-output layer, which controlled the associated motor target structures. The off-input layer supplied the off-output layer, which controlled the inverse motor structures, i.e. the motor counterparts.
The outpouch layers were initially single-layer neuron layers of projection neurons. In the course of progressive evolution, the thickness of the output layers increased. They were no longer single-layer neuron layers, but contained several layers of output neurons.
For the purpose of increasing fail-safety, the outpouch layer began to form reserve neurons. The layer thickness grew.
The input neurons of the upper off-layer were signal-compatible with the input neurons of the lower on-layer, because they had emerged from them by signal inversion and were ultimately connected to the original signals by a chain of neurons connected in series.
Therefore, the output neurons of the lower on-layer could not only receive signals from the lower input layer, but also the signals of the upper off-input layer via interneurons. The upper off-output layer slowly became superfluous in the course of evolution and regressed.
In the course of evolution, a cylindrical, relatively thick layer of output neurons formed between the two approximately circular and thin input layers. This structure thus developed into a vertical divergence module. It could now evaluate the signal strength of the receptor signals and transform them into a maximally coded signal vector. The characteristic of vertical divergence modules is the reception of direct and inverted signals at the upper and lower boundaries of the module. The input neurons are arranged relatively close together.
On the motor side, the signal divergence had to be reversed, so convergence modules developed there.
Divergent modules with vertical signal propagation appear first in evolution and are found in reptiles and birds, among others. The associated convergence modules are also vertically organised.
Stage 5: Occurrence of signal divergence in the area
In many nuclei, signal divergence also occurred in the area. The input neurons moved away from each other, while the number of output neurons increased in the area. This turned the divergence module with vertical signal propagation into a divergence module with spatial signal propagation. One consequence was the possibility to detect periodic changes in the signals, e.g. the angle of rise of a dark or coloured straight line against a background with white colour or the complementary colour. Similarly, centre-of-gravity modules became possible, allowing fine-grained motor control of rotational movements. Divergence modules with spatial signal propagation occur predominantly in mammals and reach their strongest signal divergence in primates and humans.
Stage 6: Emergence of neural body models of motor function
Stage 7: Time-delayed signals as a new modality
In progress
Level 8: Body side comparison in side change modules
In progress
Stage 9: Cerebellar storage of the current motor state
In progress
Level 10: Motor Learning
In progress
Monografie von Dr. rer. nat. Andreas Heinrich Malczan