Reason
#1: Scientists have no understanding of how neurons could make a
decision.
When
they try to present low-level explanations for a how a brain could do
some of the things that they attribute to brains, our neuroscientists
falter and fail. An example is their complete failure to credibly
explain either how memories could be encoded in neural states, how
memories could be permanently stored in brains, or how memories could
be instantly recalled by brains. Neuroscientists also cannot
credibly explain how a person could make a decision when faced with
multiple choices.
When I did a Google search for "what happens in the brain when a decision is made," I got a bunch of articles with confident sounding titles. But reading the stories I read mainly what sounded like bluffing, hype, promissory sounds, and the kind of talk someone uses to persuade you he understands something he doesn't actually understand (along with some references to brain scanning studies that aren't robust for reasons discussed later in this post). At no one point in these articles do we ever reach someone who makes us think, "This guy really understands how a brain could reach a decision."
When I did a Google search for "what happens in the brain when a decision is made," I got a bunch of articles with confident sounding titles. But reading the stories I read mainly what sounded like bluffing, hype, promissory sounds, and the kind of talk someone uses to persuade you he understands something he doesn't actually understand (along with some references to brain scanning studies that aren't robust for reasons discussed later in this post). At no one point in these articles do we ever reach someone who makes us think, "This guy really understands how a brain could reach a decision."
Let
us consider a simple example. Joe says to himself, “Today I can
either go to the library or go to see a movie.” He then decides to
go to the library, and then starts walking towards the library.
To
explain this neurally, we would have to explain several different
things:
Item
1: How Joe's brain could hold two different ideas, the idea about
the possibility of going to the movie, and the idea of going to the
library.
Item
2: The appearance in Joe's brain of a third idea, an idea that he
will go today to the library.
Item
3: Some neural act that causes his muscles to move in a way
corresponding to his idea about going to a library.
The
first two of these things cannot be credibly explained through any
low-level explanation involving neurons or synapses. See my post “No
One Understands How a Brain Could Generate Ideas” for a discussion
of the failure of neuroscientists to present any credible
explanations of how brains could generate ideas. In that post, I
cite some “expert answers” pages on which the experts address
exactly the question of how a brain could generate ideas, and sound
exactly as if they have no understanding of such a thing.
On
one of the “expert answers” pages that I cite, we have this
revealing answer:
“
'How
does the 'brain' forms new ideas?' is the wrong question. We don't
actually know how the brain codes old
ideas.”
That
is correct, which means that neither Item 1 in my list above can be
explained neurally, nor Item 2. Since we do not understand how a
brain could either hold ideas or form new ideas, we do not have any
understanding of how a brain could make a decision.
Reason
#2: Hemispherectomy patients can still make decisions just fine.
Hemispherectomy
is an operation done on patients with severe epileptic seizures. In
an hemispherectomy operation, half of the brain is removed. I can
find no studies that have specifically studied decision-making
ability in hemispherectomy patients. However, I have cited here and
here and here and here scientific papers that show results for intelligence tests taken
“before” and “after” a hemispherectomy operation. Such
papers show, surprisingly, that removing half of a brain has little
effect on intelligence as measured in IQ tests.
Written
IQ tests are typically tests of not just intelligence but also
decision making ability. For example, the Wechsler IQ test is by far
the most common one used by scientists, and it is a multiple-choice
test. Every single time a person has to pencil in one of the little
ovals in a multiple-choice test, he has to make a decision. So
standard IQ tests are very much tests of not just intelligence but
also decision-making ability (which may be considered an aspect of
intelligence).
Since
IQ tests done on hemispherectomy patients show little damage to IQ
scores after removing half of a brain, we can only conclude that
removing half of a brain has little or no effect on decision making
ability. We would not expect such a thing to be true if your brain
is what makes your decisions.
Reason
#3: Some people who lost most of their brains could still make
decisions normally.
Cases
of removal of half of the brain by surgical hemispherectomy are not
at all the most dramatic cases of brain damage known to us. There
are cases of patients who lost almost all of their brains due to
diseases such as hydrocephalus, a disease that converts brain
tissue to a watery fluid. Many such cases were studied by the
physician John Lorber. He found that most of his patients were
actually of above-average intelligence. Similarly, a French person
working as a civil servant was found in recent years to have almost
no functional brain.
Such
cases seem to show that you can lose more than 75% of your brain and
still have a normal decision making ability. This argues against
claims that your brain is what is making your decisions.
Reason
#4: Split brain patients don't have their decision making harmed.
The
two hemispheres of the brain are connected by a set of thick fibers
called the corpus callosum. In rare operations this set of fibers is
surgically severed. The result is what called a split-brain patient.
Despite the erroneous claims that are sometimes made about this
topic, the fact is that such an operation absolutely does not result
in anything like a split personality or a split consciousness or a
split mind. Such an operation does not result in two minds causing
conflicting decisions.
The scientific paper here (entitled "The Myth of Dual Consciousness in the Brain") sets the record straight, as did a scientific study published in 2017. The research was done at the University of Amsterdam by Yair Pinto. A press release entitled “Split Brain Does Not Lead to Split Consciousness” stated, “The researchers behind the study, led by UvA psychologist Yair Pinto, have found strong evidence showing that despite being characterised by little to no communication between the right and left brain hemispheres, split brain does not cause two independent conscious perceivers in one brain.” Their study (entitled "Split brain: divided perception but undivided consciousness") can be read here. “We have shown that severing the cortical connections between the two brain hemispheres does not seem to lead to two independent conscious agents within one brain,” the researchers said.
The scientific paper here (entitled "The Myth of Dual Consciousness in the Brain") sets the record straight, as did a scientific study published in 2017. The research was done at the University of Amsterdam by Yair Pinto. A press release entitled “Split Brain Does Not Lead to Split Consciousness” stated, “The researchers behind the study, led by UvA psychologist Yair Pinto, have found strong evidence showing that despite being characterised by little to no communication between the right and left brain hemispheres, split brain does not cause two independent conscious perceivers in one brain.” Their study (entitled "Split brain: divided perception but undivided consciousness") can be read here. “We have shown that severing the cortical connections between the two brain hemispheres does not seem to lead to two independent conscious agents within one brain,” the researchers said.
In
2014 the wikipedia.org article on split-brain patients stated the
following:
“In
general, split-brained patients behave in a coordinated, purposeful
and consistent manner, despite the independent, parallel, usually
different and occasionally conflicting processing of the same
information from the environment by the two disconnected
hemispheres...Often, split-brained patients are indistinguishable
from normal adults.”
In the video here we see a split-brain patient who seems like a pretty normal person, not at all someone with “two minds." And at the beginning of the video here the same patient says that after such a split-brain operation “you don't notice it” and that you don't feel any different than you did before – hardly what someone would say if the operation had produced “two minds” in someone. And the video here about a person with a split brain from birth shows us what is clearly someone with one mind, not two. In these interviews, every single time the split-brain patients answer questions normally, they are showing their ability to make decisions normally. The mere act of answering questions always involves decisions about what to say and how to say it.
But
this is not at all what we should expect from the assumption that the
brain is the source of our decisions. If that assumption were true, a
split-brain operation should cause two independent sources of
decision-making that would have a tendency to conflict with each
other.
Reason
#5: “Decision zig-zag" is almost never observed in pressure situations, but we would expect it to be very common if different parts
of the brain (or halves of the brain) were causing decisions.
1. Pick a color.
2. Pick a number between 1 and 10.
3. Pick a planet.
4. Pick a continent.
5. Pick a city.
Did you skip the test? No fair. It's easy -- go back and try it.
Now, if you are like 90% of my readers, you were able to do this exercise real quickly, in less than 10 or 15 seconds. But we would not expect such a thing to be possible if your brain was making your decisions. For in that case, we would expect that different parts of the brain would be coughing up different decisions, leading to a result rather like this:
Pick a color? Uh, red -- no green - no blue - okay, red!
Pick a number? Uh, 8! No, 6 ! No -- uh, 4! No, 2!
Pick a planet? Merc -- no Jupiter -- no, Earth, no wait...
Pick a continent? North -- no South -- no Eur -- no Afri -- no Asia!
Pick a city? New ... uh, no Shang... no Paris -- oops, no Moscow!
As mentioned above, people who have half of their brains removed in hemispherectomy operations can make decisions normally. It therefore cannot be maintained that a decision requires a full brain. If you think that brains make decisions, you are forced to the idea that part of a brain (half a brain or less) can make a decision. But such an idea makes us ask: should not then people be overwhelmed by conflicting decision signals, sent by different parts of a brain?
Consider the organization of the brain. There are two identical halves. Under the hypothesis that a half of a brain or less can make a decision, we would therefore expect to see very often something that we can call "decision zig-zag." This would involve behavior in which an organism was flipping back and forth between two possible decisions, as if two physical areas of the brain were conflicting with each other, coming to separate decisions. We would expect to see this particularly often in "coin flip" kind of decisions in which one choice is not obviously better than another.
But we rarely see such behavior in humans, whenever there is time pressure. It is true that given some important choice, and given the luxury of time to deliberate, a person may kind of go back-and-forth in his mind about what to do. For example, if you are accepted by two different colleges, you may kind of go back-and-forth in your mind, first favoring one choice, then another. But whenever there is a tight time pressure, and people know there is only a very short time for a decision, humans typically behave with very little indecision. 
Scores on standardized tests such as SAT tests are an excellent gauge of how very infrequently high-performing humans engage in "decision zig-zag" under pressure situations. In the reading and writing part of an SAT test, a student has to answer more than 100 questions in less than two hours. The questions are multiple choice questions, so doing the test requires making 100 decisions, each a decision about which of the choices to select. Each question typically requires 30 seconds or more of reading. There is very little time for indecision. Every one who performs very well on the test (in the 90th percentile or higher) is making 100 or more decisions (about which answer to choose) with very little indecision. Under such pressure situations, humans do not at all perform like they would perform if different halves or different parts of your brain were sending you different signals about what to do. Humans instead act like beings with a single unified mind. It would seem that if different parts or halves of a brain were determining what decision to make, there would be so much indecision and "decision zig-zag" that the average SAT score in the US would be at least 200 points lower than it is.
Reason
#6: There is no particular region of the brain that seems to be
crucial to non-muscular decision making.
Some
particular regions of the brain have been strongly associated with
particular functions. For example, we know that the brain stem is
strongly associated with autonomic activity that keeps the heart and
lungs working. Any major damage to the brain stem usually causes
death. We also know that the visual cortex is strongly associated
with vision. But no strong associations have been established
between any part of the brain and calm non-muscular decision making. By "non-muscular decision making" I mean the type of thing that goes on when you silently pick a number between 1 and 10 or silently choose in the morning what you will eat for dinner.
To
get an idea of how weak is the neuroscience case that your brain
makes decisions, we can look at an article in Psychology Today
entitled “The Neuroscience of Making a Decision.” After referring
to some brain region that might be involved in addiction, which has
no general relevance to the issue of whether brains make decisions,
we are referred to a study claiming that the striatum is involved in
decision-making. It's a study used that only 7 rats, Since this is
less half of the minimum number of animals per study group
recommended for a modestly convincing result, the study provides no
good evidence for a neural involvement in decision making.
Then
the Psychology Today article refers to a brain-scanning study
attempting to show that regions called the dorsolateral prefrontal
cortex and the ventromedial prefrontal cortex have something to do
with decision making. These are the two regions that are most
commonly cited as being involved in decision making. A brain scanning
study could only give robust evidence for some region being heavily
involved in some activity if it were to show a strong percent signal
change, rather than the weak signal change of only 1% or less that
brain scanning studies typically show. In this case, the study does
not even give a figure for the percent signal change. So it does not
provide any robust evidence that the the dorsolateral prefrontal
cortex or the ventromedial prefrontal cortex have something to do
with decision making
Our
Psychology Today article then concludes, having provided no real
evidence that there is any such thing as a “neuroscience of
decision making.”
This
study examined six patients with damage to the dorsolateral
prefrontal cortex, and found that they had an average IQ of 104,
above the average of 100. Since filling out a written IQ test
requires many cases of decision making (in regard to the answer
given), such a result is incompatible with claims that the
dorsolateral prefrontal cortex is some part of the brain particularly
involved in decision making. This study says, “We have studied
numerous patients with bilateral lesions of the ventromedial
prefrontal (VM) cortex” and that “most of these patients retain
normal intellect, memory and problem-solving ability in laboratory
settings.” The meta-analysis here says that the ventromedial prefrontal cortex is the region of the brain "most commonly implicated in moral decision making," but says that there is a "lack of a significant cluster of activation" in this area, meaning that it doesn't actually light up more during brain scans.
Failing to report any actual figures for percent signal changes (the number we need to know to judge whether some area of the brain is more involved in an activity), the same meta-analysis notes differences between its findings and the findings of other studies, highlighting how much these brain scan studies tend to conflict with each other. We read the following:
Another
example of a report of a supposed “neuroscience of decision making”
is a Neuroscience News article here entitled, “Researchers Discover
Decision Making Center of Brain.” We again have a reference to a
mere brain scanning study. But this time the study has a graph that gives
us the percent signal change that we need to judge whether robust
evidence has been found. The graph shows that the percent signal
change picked up by the brain scanning is only about a fraction of one
percent, about 1 part in 300. That's no good evidence for anything,
and could easily be the result of pure chance fluctuations.
Similarly
weak results are found in this study, trying to use brain scanning to
find some region of the brain more involved in decision making. The
graph shows that the percent signal change picked up the brain
scanning is only about a fraction of one percent, about 1 part in
300. That's no good evidence for anything, and could easily be the
result of pure chance fluctuations.
In
Figure 3 of the study here, we get a brain scanning result for the
percent signal change in activity for the dorsolateral prefrontal
cortex. The graph shows a signal change of only about 1 part in 300
(about .3 percent). That's no good evidence for anything, and could
easily be the result of pure chance fluctuations.
Most of the studies that claim to show neural correlates of decision making are mainly finding either neural correlates of emotion (which can often be entangled with decision making) or neural correlates of muscle activation (often paired with decision making). When I do a Google search for "neural correlates of motionless decision making," I am unable to find a single study testing such a thing.
Reason #7: There is no convincing evidence of some type of change of brain state when a calm non-muscular decision is made.
By looking at brain scans, it is impossible to reliably predict when anyone made a non-muscular decision. We should not be fooled by a certain type of brain scanning experiment with the following characteristics:
(1) The study will not be pre-registered, and will not publish in advance a specification of some particular type of brain activation signal that it is looking for (in some very specific little part of the brain) as a sign of when someone made a decision.
(2) The study will scan the brains of people as they made some decision in their minds.
(3) Scientists will then examine the brain scans, looking for some particular tiny area of the brain that was more a tiny bit more active when the decisions were made.
(4) The study will involve only a small number of subjects, maybe 10, 15, 20 or 25.
Let me explain why this type of study is not at all good evidence for anything. In any random brain there will be random fluctuations in activity from moment to moment. Let us suppose a researcher has the freedom to compare any of 200 different little areas of the brain, looking for some area that has an increase in activity during some particular moment (such as when a decision is made). We would expect that purely by chance there would be some area that would show a tiny bit more activity during the particular moment being studied, even if it is not your brain that is making a decision. Similarly, if I use a machine that can detect minute fluctuations in temperature in the livers of 20 people while they are making a decision, and I have the freedom to check 200 different little regions of the liver, I will probably be able to find some tiny liver region which (purely by chance) had a minutely higher temperature when some decision was made. But this would do nothing to show that livers make decisions.
A discussion of this issue can be found around page 23 of the technical paper here, where we read the following:
"With a plausible population correlation of 0.5, a 1000-voxel whole-brain analysis would require 83 subjects to achieve 80% power. A sample size of 83 is five times greater than the average used in the studies we surveyed: collecting this much data in an fMRI experiment is an enormous expense that is not attempted by any except a few major collaborative networks."
In other words, brain imaging studies tend to use only a fraction of the sample size they need, given the techniques they typically use. It is possible to do a reliable study with a small sample size, if you limit the analysis to only one small tiny area of the brain. But that is almost never done.
On page 33 the paper above states the following, giving us a strong reason for skepticism about brain scanning studies:
The study here is an example of the type of unconvincing study I have just discussed. The authors scanned brains, looking for change in signal strength corresponding to whether some type of decision was made. Having the freedom to check any of 200 or more brain regions (since their study was not a pre-registered study announcing its intention to look in only one little place in the brain), the authors found one or two tiny regions where there is an extremely small greater activation when a decision was made. The difference in signal strength (as reported in Figure 1 and figure 2) was only about .1 of 1 percent, which is about 1 part in 1000. But we would expect a result as good as that by chance, because of random variations in little parts of the brain, even if brains do not actually make decisions. So the study does nothing at all to provide evidence that brains are making decisions. The study say it did "whole brain analyses", but it used only 32 subjects, only a small fraction of the 83 subjects recommended above for a mere 1000-voxel "whole brain analysis" study.
On page 68 of the book "Casting Light on the Dark Side of Brain Imaging," we read about another problem in brain scanning studies:
Here is the kind of thing we would like to have in order to have convincing evidence of greater brain activity when a non-muscular decision is made:
(1) There would have to be many replicated pre-registered studies that all showed that some particular region of the brain activated at a substantially higher level when a decision was made (more than just a fraction of 1 percent).
(2) In the pre-registration declarations, published prior to the collection of any data, the study authors would have to announce that they were studying only one small region of the brain to see whether it activates more during decision making, rather than giving themselves the freedom to check any brain region they wanted in a "fishing expedition" kind of approach to produce signal variations we would expect by chance.
(3) In the same pre-registration declarations, published prior to the collection of any data, the study authors would have to commit to one exact method of data analysis, precisely spelled out, thereby depriving themselves of the freedom to keep "slicing and dicing" the brain scan data until they got a result supporting their hypothesis.
Nothing like this has occurred. Instead we have a succession of little brain scan studies (usually with low statistical power) showing minute less-than-one-percent activation increases in some region that differs from study to study, studies in which researchers are free to look for some minute signal deviation in any brain region, and free to try dozens of data analysis methods until something that can be called a neural correlation coughs up. The results of such studies are what what we would expect to get by chance even if brains are not actually making decisions.
In short, we have no robust evidence that brains make decisions. Nature never told us that decisions are made by brains. It is merely neuroscientists who told us such a thing, without ever having adequate evidence for such a claim.
Reason #8: Humans can make decisions many times more quickly than they would make if decisions were being made by brains subject to several severe signal slowing factors and severe signal noise.
If you tried my previous selection game, you probably made decisions at a rate of about one decision per one or two seconds (each time you picked one of the possibilities, you were making a decision on what to pick). If it took you 15 seconds to do that test, about two-thirds of that was reading and memory recall; and you were making a decision at a rate of about one decision per second. A baseball hitter typically makes a decision (on whether to swing) in only a small fraction of a second. According to this scientific paper, "The average speech rate of adults in English is between 150 and 190 words per minute (Tauroza and Allison 1990), although in conversation this figure may rise considerably, reaching 200 wpm (Walker 2010; Laver 1994)." Someone speaking in conversation at 200 words per minute is making decisions at a rate of three per second, each a decision on which word to use.
But we have strong reasons for believing that brains should not be fast enough for instantaneous decisions. The "100 meters per second" claim often made about brain signal speed is not at all accurate, as it completely ignores very serious slowing factors such as the 200-times-slower speed of transmission through dendrites, the very serious slowing factor caused by cumulative synaptic delays, and the additional very serious slowing factor caused by what is called synaptic fatigue. A realistic calculation of brain signal speed (such as I have made here) leads to the conclusion that brains should be far too slow to allow extremely rapid or instantaneous decisions, and that if a brain were making a non-muscular decision (not involving a reflex), it should take at least five or ten seconds for any such decision.
We also know that the brain has multiple sources of very severe signal noise, as discussed here. It would seem that all this noise would be a huge factor preventing different parts of a brain from reaching a single decision quickly, just as it would greatly decrease the chance of a classroom of 30 people reaching the same decision very quickly if all of the people were blaring different podcasts, videos and rock songs from their smartphones.
An intelligent hypothesis about human decision making is that it comes from an immaterial aspect of human beings, what is commonly called a soul or spirit. A neuroscientist will protest that it is forbidden to postulate some important reality that we cannot directly see. Such a rule is not at all followed in general by scientists. Astrophysicists and cosmologists nowadays are constantly claiming that most of the universe consists of important realities we cannot see, what they call dark matter and dark energy -- both things that have never been directly observed by any method.
Postscript: A 2021 paper is entitled "Reduced decision bias and more rational decision making following ventromedial prefrontal cortex damage." So you make more rational decisions if your front brain is damaged? That's a result incompatible with claims that your brain makes decisions. In a 2021 article a neuroscientist is quoted as saying, "You realize that neither the term ‘decision-making’ nor the term ‘attention’ actually corresponds to a thing in the brain."