Having lived in this world for quite a few decades, I am more impressed than ever by the unity and stability of the human mind. I think back on several decades of my life and I recall a great unity of my self. There have been gradual changes in my opinions slowly caused by things I have learned more and more about, and also things I have experienced. But this has all felt very much a gradual change in a single mind. Never once did I ever feel that I was in some sense a different person than the person I was a day ago or a week ago.
So it is for the average person. There may be rare mental illnesses that involve something like a split personality, but for almost all of us nothing like that occurs. Human beliefs are remarkably stable, often to the point of stubbornness. The stability and unity of the human mind comes into play when trying to get people to pay attention to a blog site like this one. I have on this site very many arguments and very much evidence contradicting the claim that the brain is the source of the human mind. But there are so many people who refuse to examine such arguments and evidence. It seems that there are so many people in their fifties and sixties and seventies who keep believing decade after decade what they were told in college, and who kind of are saying to themselves, "I've been believing this doctrine for decades, so I'm sure not going to change my mind now."
Such inertia of belief is a difficulty for someone like myself trying to challenge old dogmas. But at least such inertia helps show the reality of what I am arguing for at this particular moment: that human minds are remarkably stable things, and typically show very great stability and unity over decades. The unity of the human mind is something we take for granted, because it has been such a stable feature of our lives, as stable as the feature of vision or hearing. But with some imagination, we can imagine human life as a very different affair.
For example, people might flip-flop around in their political views from one month to the next. People might change their views or religion from one month to the next, one month being an atheist, the next month being a Christian, and the next month being a Buddhist. Or people might always be switching the objects of their affection from week to week, like some fickle ever-changing Lothario who switches his beloved four times a month . In that case we would probably never have marriages lasting for decades. Or, whenever people made decisions it might usually be a very zig-zag affair, like illustrated in the diagram below:
Such is not the human reality we observe. In general, human minds are remarkably stable and unified, and the persistence of beliefs, attitudes and emotions over a period of 40 years or 50 years is very common. But in the brain do we have a physical reality matching this unity and stability? We do not.
A person examining brain scans of an adult at different decades in his life might claim to observe stability, with little change. But at the microscopic level, it is an entirely different story. Brains are made mainly of neurons and units called synapses that connect neurons. The proteins that make up neurons and synapses are not at all stable. Instead they have average lifetimes of only a few weeks.
A scientific paper states, "Recent studies have revealed that most proteins, including synaptic proteins, have half-lives that range between 5 and 7 days (Cohen et al., 2013, Dörrbaum et al., 2018)." The average lifetime of a protein is about twice its half-life.
The 2018 paper here is entitled "Brain tissue plasticity: protein synthesis rates of the human brain." It tells us the astonishing fact that proteins in the human brain are replaced at a rate of 3% to 4% per day. We read this:
"Where skeletal muscle tissue has been shown to turnover at a rate of 1–2% per day, here we show that brain tissue turns over much faster at a rate of 3–4% per day. This would imply complete renewal of brain tissue proteins well within 4–5 weeks. From a physiological viewpoint this is astounding, as it provides us with a much greater framework for the capacity of brain tissue to recondition. Moreover, from a philosophical perspective these observations are even more surprising. If rapid protein turnover of brain tissue implies that all organic material is renewed, then all data internalized in that tissue are also prone to renewal. These findings spark (even) more debate on the interpretation and (long-term) storage of data in neural matter, the capacity of humans to consciously or unconsciously process data, and the (organic) basis of our own personality and ego. All of this becomes quite remarkable in light of such rapid protein turnover rates of the human brain."
A scientific paper states this:
"Experience-dependent behavioral memories can last a lifetime, whereas even a long-lived protein or mRNA molecule has a half-life of around 24 hrs. Thus, the constituent molecules that subserve the maintenance of a memory will have completely turned over, i.e. have been broken down and resynthesized, over the course of about 1 week."
Research on the lifetime of synapse proteins is found in the June 2018 paper “Local and global influences on protein turnover in neurons and glia.” The paper starts out by noting that one earlier 2010 study found that the average half-life of brain proteins was about 9 days, and that a 2013 study found that the average half-life of brain proteins was about 5 days. The study then notes in Figure 3 that the average half-life of a synapse protein is only about 5 days, and that all of the main types of brain proteins (such as nucleus, mitochondrion, etc.) have half-lives of 15 days or less. The 2018 study here precisely measured the lifetimes of more than 3000 brain proteins from all over the brain, and found not a single one with a lifetime of more than 75 days (figure 2 shows the average protein lifetime was only 11 days).
The paper here states, "Experiments indicate in absence of activity average life times ranging from minutes for immature synapses to two months for mature ones with large weights."
A neuron in the brain may be compared to some house held by a remodeling enthusiast who keeps tearing down rooms and replacing them with different rooms. The synapses in the brain may be compared to something even more unstable. The average width of a synapse (only about 500 nanometers) is about 1000 times less than the average width of a neuron. Given how small synapses are (1000 times less wide than neurons), and given the very rapid turnover rate of synapse proteins (which have average lifetimes of a few weeks or less), it is very unlikely that any particular synapse lasts for years.
There is another way in which the brain fails to physically qualify as a stable unity. Neurons in the brain are connected by dendrites and synapses, and the connection is not a continuous material connection. Every synapse has a physical gap. Below is a schematic diagram of a synaptic gap:
The number of these synaptic clefts (also called synaptic gaps) in the brain is enormous. It has been estimated that the human brain has about 90 billion neurons, and about 100 trillion synapses. So there are something like 1000 synapses for every neuron. Each one of these synapses is a break in the physical unity of the brain.
The brain isn't like a continent. It's more like some huge archipelago, consisting of countless little islands. Synapses are like the gaps between the islands in the visual below.
Clearly the brain is not a stable unity. There is another reason for thinking that the brain is not a stable unity: the fact that the brain consists of two separate hemispheres:
It is true that there are fibers connecting these hemispheres, but the physical organization of having two hemispheres is another physical reason for thinking that the brain has no great unity.
There are many humans that exist as stable unified minds even though there is the most dramatic physical disunity in the brain. These are the people who have brains existing as two separate hemispheres that are not connected.
A normal human brain consists of two halves called hemispheres, which are connected by a set of fibers called the corpus callosum. However, the corpus callosum fails to develop in many people. Such a condition is called agenesis of the corpus callosum. People lacking a corpus callosum have basically two separate brains inside their skull. Does this result in two minds, as we would expect under the theory that the brain makes the mind? No, people lacking a corpus callosum have a single, unified mind.
Agnesis means a failure of something in a developing child during a mother's pregnancy. The paper
here is entitled "Outcomes Associated With
Isolated Agenesis of the Corpus Callosum: A Meta-analysis." The paper distinguishes between what it calls "cACC" and "pACC," defining cACC as complete agenesis of the corpus callosum (in other words, the total failure of the corpus callosum to appear) and defining pACC as partial aegnesis of the corpus callosum (partial failure of the corpus callosum to appear). The paper gives us these statistics, telling us that in only a relatively small minority of cases of a complete congenital absence of the corpus callosum are there cognitive problems:
"In cACC, chromosomal anomalies occurred in 4.81% (95% confidence interval [CI], 2.2–8.4) of the cases. Gross and fine motor control were abnormal in 4.40% (95% CI, 0.6–11.3) and 10.98% (95% CI, 4.1–20.6) of the cases, respectively, whereas 6.80% (95% CI, 1.7–14.9) presented with epilepsy. Abnormal cognitive status occurred in 15.16% (95% CI, 6.9–25.9) of cases. In partial ACC, the rate of chromosomal anomalies was 7.45% (95% CI, 2.0–15.9). Fine motor control was affected in 11.74% (95% CI, 0.9–32.1) of the cases, and 16.11% (95% CI, 2.5–38.2) presented with epilepsy. Cognitive status was affected in 17.25% (95% CI, 3.0–39.7) of cases."
So in only about 16% of the subjects with a complete lack of a corpus callosum was there an abnormal cognitive status. These cACC (complete agenesis of the corpus callosum) people were basically people with two separate brains in their skulls. But most of them apparently had normal unified minds, since the paper says that only 15% of them had an abnormal cognitive status.
"Case I. — Dr. Alexander Bruce reports a man of ordinary intelligence and good character, and who, for thirteen years, did the work of a porter with perfect satisfaction, and exhibited no notable peculiarities. Yet in this man the corpus callosum was completely absent (23).
Case II. — Malinverni reports a soldier, aged 30 years, of ordinary intelligence, but with a slight tendency to melancholia, who had complete absence of the corpus callosum (24).
Case III. — Eichler reports a laborer, 43 years of age, married, diligent and capable, a good husband, sober and quiet, and could read and write, yet he had no corpus callosum, and had other important malformations of the brain (25)."
We have three cases of people with no corpus callosum, meaning that they had two separated hemispheres of the brain. But in each case their mind seemed normal.
Sometimes to prevent seizures, the entire corpus callosum is surgically severed. This is sometimes called a split brain operation. The operation leaves patients with a single unified self. Insinuations to the contrary sometimes made by materialists are an example of severe deception.
Physician Michael Egnor states the following about Sperry's research:
"The neuroscientist Roger Sperry studied scores of split-brain patients. He found, surprisingly, that in ordinary life the patients showed little effect. Each patient was still one person. The intellect and will – the capacity to have abstract thought and to choose – remained unified. Only by meticulous testing could Sperry find any differences: their perceptions were altered by the surgery. Sensations – elicited by touch or vision – could be presented to one hemisphere of the brain, and not be experienced in the other hemisphere. Speech production is associated with the left hemisphere of the brain; patients could not name an object presented to the right hemisphere (via the left visual field). Yet they could point to the object with their left hand (which is controlled by the right hemisphere). The most remarkable result of Sperry’s Nobel Prize–winning work was that the person’s intellect and will – what we might call the soul – remained undivided. The brain can be cut in half, but the intellect and will cannot. The intellect and will are metaphysically simple."
The actual facts about split-brain surgery are related here by a surgeon who has performed such an operation. He states this about split-brain patients:"After the surgery they are unaffected in everyday life, except for the diminished seizures. They are one person after the surgery, as they were before."
The surgeon states: "In a rational scientific community in which evidence and reason held sway, split-brain surgery would be hailed as compelling evidence for dualism and the immateriality of the intellect and will."
