Das Selbst als biologisches System

Steven Pinker schreibt in „The Blank Slate“ eine interessante Passage zum menschlichen Gehirn:

Educated people, of course, know that perception, cognition, language, and emotion are rooted in the brain. But it is still tempting to think of the brain as it was shown in old educational cartoons, as a control panel with gauges and levers operated by a user — the self, the soul, the ghost, the person, the “me.” But cognitive neuroscience is showing that the self, too, is just another network of brain systems.

The first hint came from Phineas Gage, the nineteenth-century railroad worker familiar to generations of psychology students. Gage was using a yard-long spike to tamp explosive powder into a hole in a rock when a spark ignited the powder and sent the spike into his cheekbone, through his brain, and out the top of his skull. Phineas survived with his perception, memory, language, and motor functions intact. But in the famous understatement of a co-worker, “Gage was no longer Gage.” A piece of iron had literally turned him into a different person, from courteous, responsible, and ambitious to rude, unreliable, and shiftless. It did this by impaling his ventromedial prefrontal cortex, the region of the brain above the eyes now known to be involved in reasoning about other people. Together with other areas of the prefrontal lobes and the limbic system (the seat of the emotions), it anticipates the consequences of one’s actions and selects behavior consonant with one’s goals.30 Cognitive neuroscientists have not only exorcised the ghost but have shown that the brain does not even have a part that does exactly what the ghost is supposed to do: review all the facts and make a decision for the rest of the brain to carry out. Each of us feels that there is a single “I” in control.

But that is an illusion that the brain works hard to produce, like the impression that our visual fields are rich in detail from edge to edge. (In fact, we are blind to detail outside the fixation point. We quickly move our eyes to whatever looks interesting, and that fools us into thinking that the detail was there all along.) The rain does have supervisory systems in the prefrontal lobes and anterior cingulate cortex, which can push the buttons of behavior and override habits and urges. But those systems are gadgets with specific quirks and limitations; they are not implementations of the rational free agent traditionally identified with the soul or the self.

One of the most dramatic demonstrations of the illusion of the unified self comes from the neuroscientists Michael Gazzaniga and Roger Sperry, who showed that when surgeons cut the corpus callosum joining the cerebral hemispheres, they literally cut the self in two, and each hemisphere can exercise free will without the other one’s advice or consent. Even more disconcertingly, the left hemisphere constantly weaves a coherent but false account of the behavior chosen without its knowledge by the right. For example, if an experimenter flashes the command “WALK” to the right hemisphere (by keeping it in the part of the visual field that only the right hemisphere can see), the person will comply with the request and begin to walk out of the room. But when the person (specifically, the person’s left hemisphere) is asked why he just got up, he will say, in all sincerity, “To get a Coke” — rather than “I don’t really know” or “The urge just came over me” or “You’ve been testing me for years since I had the surgery, and sometimes you get me to do things but I don’t know exactly what you asked me to do.” Similarly, if the patient’s left hemisphere is shown a chicken and his right hemisphere is shown a snowfall, and both hemispheres have to select a picture that goes with what they see (each using a different hand), the left hemisphere picks a claw (correctly) and the right picks a shovel (also correctly). But when the left hemisphere is asked why the whole person made those choices, it blithely says, “Oh, that’s simple. The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed.” The spooky part is that we have no reason to think that the baloney-generator in the patient’s left hemisphere is behaving any differently from ours as we make sense of the inclinations emanating from the rest of our brains. The conscious mind — the self or soul — is a spin doctor, not the commander in chief. Sigmund Freud immodestly wrote that “humanity has in the course of time had to endure from the hands of science three great outrages upon its naïve self-love”: the discovery that our world is not the center of the celestial spheres but rather a speck in a vast universe, the discovery that we were not specially created but instead descended from animals, and the discovery that often our conscious minds do not control how we act but merely tell us a story about our actions. He was right about the cumulative impact, but it was cognitive neuroscience rather than psychoanalysis that conclusively delivered the third blow. Cognitive neuroscience is undermining not just the Ghost in the Machine but also the Noble Savage. Damage to the frontal lobes does not only dull the person or subtract from his behavioral repertoire but can unleash aggressive attacks. That happens because the damaged lobes no longer serve as inhibitory brakes on parts of the limbic system, particularly a circuit that links the amygdala to the hypothalamus via a pathway called the stria terminalis. Connections between the frontal lobe in each hemisphere and the limbic system provide a lever by which a person’s knowledge and goals can override other mechanisms, and among those mechanisms appears to be one designed to generate behavior that harms other people.

Das spricht meiner Meinung nach durchaus dafür, das unser „Ich“ eine Konstruktion unseres Gehirns ist, welche das Gehirn nach Kräften aufrechterhält. Es werden Verhalten und Sinneseindrücke so eingeordnet, dass sie mit unserem Selbstbild übereinstimmen und uns logisch erscheinen. Das Gehirn ist in der Lage uns eine künstliche Realität vorzugaukeln und unser Denken so zu formen, wie es für uns aus dessen Sicht besser ist.

Dabei ist zu bedenken, dass diese vom Gehirn vorgegaukelte Realität bei fehlen bestimmter Gehirnfunktionen anders aussieht als die eigentliche Realität. Nachdem Phineas Gage ein Frontalhirnsyndrom zeigte wich sein Selbst und damit auch seine subjektive Realität von der der anderen ab. Aus dem besonnenen, freundlichen und ausgeglichenen Gage wurde ein kindischer, impulsiver und unzuverlässiger Mensch.

Interessant ist, was mit dem Frontalhirn geleistet wird:

Allgemein schreibt man diesen Hirnteilen, die auch als präfrontaler Cortex bezeichnet werden, eine Analyse- und Überwachungsfunktion zu. Daher wurde für ihn auch der Begriff „supervisory attentional system“ (SAS) eingeführt. Es besteht ein dichtes Netzwerk zu vielen anderen Hirnteilen. Auf diese Weise können unterschiedlichste Informationen analysiert, bewertet, „verrechnet“ und die Ergebnisse wieder zurück gesendet werden – ähnlich dem zentralen Prozessor (CPU) eines Computers. Aufgrund der zahlreichen präfrontalen Verbindungen („Projektionen“) zu anderen Gehirnstrukturen können auch Läsionen in anderen Hirnabschnitten zu einem Dysexekutiven Syndrom führen, z. B. Thalamus, kortikale oder subkortikale limbische Strukturen, Basalganglien.

 Das Gehirn selbst kann die Daten nicht mehr verarbeiten, die Daten erscheinen daher Fehlerhaft im Ich bzw. Selbst. Aus rein biologischen Gründen denkt der jeweilige Mensch andere Gedanken und verhält sich anders, wobei ihm dies normal vorkommen wird.