Игорь Волков – Hardware and software of the brain (страница 5)

2 key blocks of the limbic system are the amygdala and the hippocampus. They are very different and seemingly complement each other. The amygdala is a typical subcortical structure. It is linked to generation of very basic states of the organism as a whole – such as fear and aggression. The hippocampus is the archicortex. This is a small piece of cortical matter which emerged early in evolution and has just 3 layers. Thus it should perform some important functions. An interesting theory of the hippocampus is as follows. What you usually see in illustrations (CA1, CA3, etc.) is a cross-section. The hippocampus as a whole is a tube or more precisely – a long cone in correspondence to its name Cornu Ammonis. Functionally, the hippocampus generates a 1D image that is a vector. The index of this vector goes along the tube while its cross-section provides a pathway for data rotation. Input comes from the entorhinal cortex, output returns back to it. That is, the entorhinal cortex may be a memory buffer which can receive an image from a wide variety of cortical regions, then keep it for temporary dynamical storage via reverberation through the hippocampus. Thus, the hippocampus may work as famous operative memory. Note that it can't store data because it is 1D, while cortical images are usually 2D. Only plays some important role in this storage. In addition to that loop, another major output of the hippocampus goes via the fornix to several small (0D that is scalar) areas of the brain. Through the mammillary bodies, the hippocampus can control the thalamus. It also sends output to the septum (a pleasure zone). There are several such spots in the brain (the substantia nigra, ventral tegmental area). They use the neuromediator dopamine which can control formation of long-term memory.

At last, need to discuss the relation of the brain processor to such important psychological concepts as motivation and consciousness. For humans, motivation is more than just a Start button which sets the goal and launches processing. Human problem solving reduces the main task to subtasks. Accordingly, motivational structures will be activated in the process again and again. There are 2 different types of human motivation – biological needs and goals of behavior. They are generated in the hypothalamus and the prefrontal cortex respectively. The former is a standard part of the limbic system, while some authors include the prefrontal cortex too. In any case, it is linked to the limbic structures.

As to consciousness, this term may be used in different meanings. The most primitive is just the state of awakeness as opposed to sleeping. Accordingly, in the latter case, activational structures of the brain simply switch off perception and data input stops. In a more subtle meaning, consciousness is the ability of the brain to watch itself. This is usually linked to the TPO (Temporal-Parietal-Occipital) zone of the neocortex – an area where 3 main sensory analyzers come together and create a synthetical image of reality. The associative cortex is interlinked with the entorhinal cortex thus receiving information from other parts of the brain and we can look not only at the external world but also at our own internal activity.

Fig. 12.

This is a processor of the brain aka the limbic system. Emotions serve as processor instructions for an associative computer. How does it work? Let's formulate the answer in advance.

The amygdala and hippocampus complement each other. The first generates various states of the brain that are appropriate for a particular situation. The second outputs sharp bursts of activation to trigger these states, switch, or end them.

Theory of automatic regulation helps to decode this overcomplicated pile. According to this approach, the whole of the brain's computer is a supplement to the hypothalamus which in turn is the highest control center for internal organs. The first simplification is to remove the arrow from the amygdala to the hypothalamus. The link in this direction ensures that emotions produce reactions in the body so it is already beyond the psyche. Instead, the reverse link is a key because it conducts activated biological needs and launches generation of appropriate emotions.

Fig. 13.

All in all, the brain processor has 2 major functions: managing dynamic operative memory and suppressing unnecessary associations. The second function works as follows. When some event comes to sensory inputs, it is evaluated by the limbic system. If it is important – passed further, otherwise blocked. For the valuable events, the limbic system (amygdala) determines blocks of associative memory which should be used for processing. Others are inhibited. That is, for each event the amygdala outputs a pattern of active cortical regions. The principle of dynamic memory via recirculation may be used to store sensory images and these emotional patterns too. In this case, the loop is linked within limbic structures.

Both processes (selection of events and selection of associations) are modulated by the input from the hypothalamus and the prefrontal cortex, that is by primary needs and current goals.

Fig. 14. The functional scheme of the brain processor. Blue links represent static signals which provide information about context. They also may be quasistatic. That is, may change gradually so that at any moment some definite state is processed. Red – distinct pulses known in programming as events. Reciprocal connections at both sides of the entorhinal cortex represent dynamic (operative, working) memory. By this means, an image may be retained even when the initial sensory input disappears. Motivation comes to the amygdala from 2 sources – the hypothalamus and the output half of the neocortex.

Software

Software and behavior is not the same. The latter is objective reality while the former is an invisible nonmaterial component which is responsible for generation of this reality. That's what biology could not understand for centuries. Materialism required "objective" methods and tangible evidence, but everybody knows that software is not just an essential part of a computer, but its main part. Any complicated computer without software is dead, simply useless. Research of brain anatomy quickly revealed existence of input and output channels, but what's next? Reflex? Too primitive for the human psyche. The concept of software resolves this problem. Reflex is only the simplest way to link input and output. Real neurocomputers use much more complicated methods.

What is brain software? In a computer, it consists of binary codes representing processor instructions and some data which accompany these codes. Brain operation is manipulating images. They emerge in some parts, migrate to others, are transformed, and interact with each other. To establish correspondence, we can look what happens in the end. In a computer, data usually arrive to a display and are presented as text, charts, or visual images. In the brain, internal images of movements come out to muscles. So abstract images of the nervous system are data being processed, but where are instructions? They are absent. This is possible because the brain uses associative memory which is capable of some processing too. For example, an instruction set of a typical processor has arithmetical operations which are learned by humans only later. Conditional branching is implemented by memory at hardware level in parallel mode and there is no special command for it. The instruction set of the brain (if any) is much smaller than that of computer. Then, how are programs stored? In associations. The nervous system is able to remember sensory or abstract images and associate them with each other.For computers, this is known as the rule-based programming style and is also used in the event-driven paradigm. Programmers associate important events with appropriate event-handlers.

Neuroprogramming

With that said, the picture of brain software as a whole turns out to be very different as well. For a computer with the single processor, talks is about linear programming that is executing a sequence of instructions. For multiprocessing it will be just several lines running in parallel. For humans, this is different. The brain has a complicated internal structure, but consists of simple blocks. Namely – more or less homogeneous neural nets linked by beams of white matter. These nets can learn some patterns of activity which may be triggered by incoming signals. All in all we get a complicated system of non-synchronized rules which work in parallel both at application and system level.

This is only the first approximation. Don't forget that the brain is an analog system. So far, we used discrete concepts which are applicable with a certain precision. If we try to dig into details, various transitional processes emerge. In a computer, signals are represented by sharp pulses of almost rectangular form. In the nervous system, pulses are much longer and have sloped edges. What is essential, this is not just imperfect representation. Deviation from strict discreteness is functionally significant and used time by time. Borrowing from physics, this may be dubbed as "quantum effects" in cybernetics. For example, suppose you drive a car and need to enter a gate. At one moment you notice that you have missed and one side will be 1 centimetre into the post. It is necessary to stop, move backwards, and try again. Now imagine the same situation, only walking on foot. If your shoulder is going to hit the post, you will slightly deflect the body and pass successfully. Quantum tunnelling. Such effects become vitally important in real-world conditions where strict rules would often encounter various obstacles. Without "corrections" and "exclusions" control systems would stop again and again.