tbi2

The silent interpreter

In the healthy human brain, a silent interpreter completes his job minute for minute, day for day. He understands our feelings and explains them to our reason, and vice versa he finds the best arguments to keep our feelings under logical control. He shares his fate with several inconspicuous helpers: we notice their assistance only if they suspend their valuable service for any reason.

The human brain has come a long developmental way. Basically, brains in all species try to make the best of the sensory input to guide the most appropriate motor output. Some urgent decisions (‘reflexes’) travel the shortest possible way between the senses and the muscles, for example retracting a limb from a source of damaging heat. Here, the neuron signaling ‘contraction’ to the muscle fibers in the affected limb lies side by side as close as possible to the neuron receiving temperature information from the same limb. These neurons are aligned from neck to bottom in the ‘spinal cord’, somehow representing the brains elongation down to the lower parts of the body. With some delay, the information is also forwarded to the higher operative units inside our skull, but the immediate reaction is executed without waiting for any comment from there. Species with fast reactions to life threatening dangers had better chances to survive (actually, only those with such fast reactions did survive).

This is not the only hierarchical subdivision in the brain. The upper part is organized in ‘lower’ and ‘higher’ levels. The ‘brain stem’ connects the spinal cord to the main brain and controls such vital functions as heart rate and respiration (also these activities need no further comment from above). At the highest level, sensory information from the whole body is received by neurons in the outer layer of our brain (the ‘cerebral cortex’), and neurons in areas nearby project downwards to control these body parts. Each limb of the body has its own representation in the cerebral cortex (the sensory and the motor ‘homunculus’). After a stroke, bodily functions may be affected in a distinguished way: upper or lower extremities, left or right half of the body. In the human brain, a large fraction of the neurons in the cerebral cortex is free of all prescribed duties; these top-level-participants receive their assignments during maturation. They supervise and instruct their neuronal colleagues in other, more specific cortical areas.

In brain research, these two levels of organization, the spinal cord and brain stem on one side, and the cerebral cortex on the other, have been studied in fair detail. There are intermediary levels between them (usually summarized as ‘subcortical’), and much less is known about these. A large heap of numerous interconnected nuclei in toto referred to as the ‘thalamus’ lies in the middle of the brain. Its main role seems to be the sorting and channeling of signals between cerebral cortex and spinal cord. Around this central bunch lie in roughly circular arrangement several brain regions termed the ‘limbic system’, among them the ‘hippocampus’ specialized for short-term-memory and the ‘amygdala’ composed in itself of various nuclei (just to mention the most prominent components). Activation of the latter induces fear. Rare cases with a selective loss of the amygdala (Urbach-Wiethe disease) lack fear and approach trustfully each stranger (mostly to their disadvantage).

The limbic system is able to subject standard situations of high relevance to a shortened accelerated protocol. This role is somehow reminiscent of the spinal cord reflex loop mentioned in the beginning, just on a higher level. In animals, these pre-programmed processes dominate most behaviors. In most situations, the limbic system is ready to handle any problem, and no advice from a higher level is needed. We experience these events as feelings or emotions. They convey to us the pressing need to act in a specific way without much sensibility to logical argument. In humans, however, logical argument is of greater influence than in animals. The human brain has large areas in the cerebral cortex not reserved for specific tasks (in the prefrontal cortex). Interconnection between the limbic system and these general purpose higher level domains allows the rational control of spontaneous urges. Then, some ‘inner voice’ seems to tell us: “Yes, it’s frightening, but it looks more dangerous than it really is. You did that before and it always turned out fine”.

Experience may instruct circuits in the human prefrontal cortex in several routines leading us through delicate situations that otherwise would alarm our limbic system. We can stay ‘cold blooded’ and ‘keep our nerves’ in spite of signals heralding danger. The most important pathway for this top down control seems to be the connection between the amygdala and the orbitofrontal cortex. So to say: the limbic system has chosen the amygdala as its speaker to attract the attention of our reason, and reason has delegated the orbitofrontal cortex as the most appropriate to translate higher level arguments into the simple language that is needed to be taken serious by the rather ill-mannered limbic system. The need for specialized interpreters comes from the fundamental difference in the basic architecture of the two systems. While the lower level limbic system is composed of specific modules representing various physiological parameters (it has close associations with the hypothalamus and with olfaction), the prefrontal cortex has a more homogenous setup. From an information processing point of view, the former evolutionary much older principle is based on analogue processing while the latter, more recent development prefers the digital way.

In the biological evolution of information processing, speed is of utmost significance. Although logical thinking should in general find best solutions for all sorts of problems, it often takes too much time. Some problems take a whole human lifetime to be solved, others even many generations. But thanks to culture and tradition, and thanks to the long period a human brain takes to mature, we can make progress. While the limbic system was the best solution to support the survival of individuals, reason combined with communication and tradition puts more weight on the success of homo sapiens as a species. We need to stand together as social beings to solve our problems. The challenge for each human is to make the best of both worlds: of our spontaneous urge pressing us to succeed as an individual, and of our desire to contribute to the success of the community. Our brain – thanks to millions of years of evolution – is in the position to tackle both tasks. Thanks to smooth communication between the general purpose prefrontal cortex and the archaic limbic system we can train our brain to respond to pressing needs as fast as the primitive system was able to, but not necessarily in the same way. We experience people with this aptitude as well educated and good-mannered and appreciate their style.

On the other hand, we have a critical eye for conspecifics all too often giving way to spontaneous desires arising from lower level sources. This may be the result of a lack of appropriate education and may improve with the patient investment of attention and empathy; in other cases, however, the substrate necessary to profit from such interventions is incomplete or missing. Sometimes this defect is hereditary (as in Urbach-Wiethe disease mentioned above), but more often traumatic brain injury (TBI) lies at the root. The narrow pathway connecting the orbitofrontal cortex to the amygdala is sensitive to shearing force and to intruding shreds. After disconnection, it will be difficult or impossible, depending on the extent of the damage, to continue the buildup of memory traces in the prefrontal cortex as the product of reasonable comments on the spontaneous and often immodest suggestions arising from the limbic system. The treasure of valuable routines accumulated already can further be used and can even be extended, but new experiences can no longer be processed as easily as before.

Subjects suffering from such a defect may have difficulties to lead an independent successful life. Depending on the age when the incident happened, their personality as an adult will meet with more or less acceptance by their social environment.

Mastering our selfish ego allows us to play a satisfying role in the community. Our own well-being is always linked to the well-being of others. What we do for them and what they in return do for us is a matter of – largely silent – contracts. We rarely need ‘pen and paper’ to cope with our acquaintances. Many agreements even go without words. We learn each other’s cues and signs. The fewer words we need, the better runs smooth cooperation. 99% of our social interactions follow a routine protocol without much emotional or rational investment. We tend to forget how much time and diligence it took to establish them. If you remember the preceding paragraphs of this text, you will not be surprised to learn that human communication in various settings heavily relies on easy and fast translation of verbal and non-verbal contents from the formal to the emotional level and back (during forging the adequate reply or reaction). People with compromised traffic between reason and feelings are often incapable to handle a challenging exchange of arguments ‘online’. Rather, they withdraw from the contact and deal with the topic in decent privacy (‘offline’). Mostly, their cognitive abilities are intact (if not superior) and they are eager to continue the dispute sometime later, but in the meantime their vis-à-vis may have lost interest. They often understood the (transient) withdrawal either as impolite or as a simple form of expressing agreement.

Each personal experience at first comes to us in our private inner world. We can share our experience with others only if we manage to translate it into any transmittable code that is understood and can be decoded by a communication partner. This requires the transformation of our original experience (in all its rich composition of flavors, sounds, smells, colors, dissonance or consonance with our expectations, story behind it, similarities to other experiences) into a chain of phonemes and/or a pattern of non-verbal gestures and facial expressions. The first (inner) world is accessible to our attention by virtue of the various parts of the limbic system, with tight relation to bodily sensations. If it comes to making understand a partner what exactly our primary feelings were, our message has to use his or her receptive ‘enter-port’, like signals can be fed into a PC by addressing the adequate port. Therefore, the greatest part of our original experience will be ‘lost in translation’ and only the bare bones of it will enter the connecting channel. At the other end of the line, a feeling mind is trying to make sense of these ‘bare bones’. We immediately understand the difference between the true content and the ‘bare bones’ of a conversation if we listen to a dialogue in a language we are not familiar with.

The first brain areas confronted with a verbal or non-verbal communication are our sensory cortices: Wernicke’s area in (mostly the left) temporal lobe, the primary visual area in the occipital cortex; and ‘mirror neurons’ near Broca’s area in (mostly the left) frontal cortex. To catch the meaning of the received information, however, the content has to be confronted with the inner world of the receiver. The road to this inner world goes by the prefrontal cortex and its orbito-frontal constituent to the sub-cortical amygdala and further to the rest of the limbic system. Once this journey is complete, the partner will understand and will – to some extent – share the feeling. Thus, any exchange of opinions satisfying both partners depends on the frequent execution of a rather complex protocol in two brains. If just one tiny pathway in one of these brains is handicapped, the door is wide open for misunderstanding and disdain.

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