There is no robust evidence that memories are stored in brains, but every now-and-then the press claims that some scientists have done something they could only do if memories were stored in brains. Maybe a claim is made that memories were erased from a brain, or maybe a claim is made that memories were implanted in a brain, or maybe a claim is made that memories were transferred from one brain to another. It will inevitably be true that if you examine the research in detail, you will find that no robust evidence has been produced for any such thing. Such research suffers from the types of flaws discussed here.
Given that there are many thousands of neuroscientists funded with so many hundreds of millions of dollars of research money, we should expect that exactly such reports would occasionally appear, even if memories are not stored in brains. In considering matters such as these, I like to remember a particular rule:
The rule of well-funded and highly motivated research communities: almost any large well-funded research community eagerly desiring to prove some particular claim can be expected to occasionally produce superficially persuasive evidence in support of such a claim, even if the claim is untrue.
For example, if there were a group of 40,000 researchers who were believers in Bigfoot creatures, and such a group were to each year receive hundreds of millions of dollars in funding for their research, we should then expect to occasionally get superficially persuasive evidence in support of the existence of Bigfoot creatures, even if they don't exist.
Sometimes an idea may seem fairly believable when it is painted in broad brushstrokes, but we may recognize the idea as being untenable once we start to examine the idea in detail. When a small child loses a tooth, her mother may tell her the story of the Tooth Fairy. “Just place the tooth under your pillow,” says the mother, assuring the child that when she wakes up there will be some cash under her pillow and that the tooth will be gone, because of the action of the Tooth Fairy. The next morning the child will probably be woken up by her mother, who will report finding some cash under the pillow. The story of the Tooth Fairy doesn't seem too unbelievable, unless the child subjects the story to detailed scrutiny. For example, she might ask: how could the Tooth Fairy ever have known that I had lost a tooth? Or she might ask: how could the Tooth Fairy ever have known where I lived, or removed the tooth and placed the money, without waking me up? After such scrutiny the child may realize that the mother probably just removed the tooth and put the money under the pillow when she woke up the child .
Like the story of the Tooth Fairy, the story that memories are stored in brains does not sound very unreasonable if we hear the claim painted in broad brushstrokes. It is when we start to subject this claim to detailed scrutiny that all types of credibility problems arise.
Let us consider two of these credibility problems: that a brain would never exactly where to read a memory, and that a brain would never know exactly where to write a memory.
Problem #1: A Brain Would Never Know Exactly Where to Read a Memory
One of the worst problems associated with the idea that a brain stores memories is what I call the navigation problem. The navigation problem is the problem that if a memory or some particular piece of knowledge was stored in your brain, your brain would never know where exactly to read that exact memory.
Let's consider an example. You are in school, and you come to a test question asking about some particular human, perhaps a scientist or a general or the leader of a country. You then have to recall what you know about that person. Under the theory that our brains store memories, such information would presumably be stored in some exact tiny spot in your brain. But for you to answer the question using the brain to retrieve a memory, your brain would presumably have to know the exact tiny spot where to read that information. How could the brain possibly know where that exact spot was, so that you instantly recall the memory?
I can imagine an extraterrestrial organism for which such a thing would be easy. It might work like this. The organism might have memory addresses, a position location system with numerical identifiers for each of the little storage locations (comparable to post office boxes in a gigantic post office). So when the organism formed a new memory, it might put that memory into some numbered storage location (for example, memory slot #822,235). Also, when the organism formed a new memory, it would always be associating these memory addresses with particular names, facts, and faces. So, for example, if the organism formed a new memory that Jokonto was the ruler of Zunando, then it would always remember a particular number (such as #532,233) that it would associate with the name Jokonto. Then when the organism heard the name Jokonto, it would remember that memory address and read the information from exactly that tiny little spot in its brain (memory slot #532,233 in this example).
But nothing like this can be occurring in the human brain. Particular neurons in the brain are not addressable. There is no position location system that could possibly be used by the brain to identify the exact tiny location of a stored memory. Also, humans do not at all remember any numbers associated with a storage location in the brain. I may learn the fact that George Patton was a skilled general during World War II, but I do not at all learn any “brain location coordinate” or location address that I associate with the name of George Patton, some neural location number that I could use to instantly retrieve the exact location of the information that I had learned about George Patton.
So if a memory or learned information is stored in some exact spot of the brain, how could your brain ever instantly find that exact spot? It seems that it could never do this. The brain would never know the exact spot to read a particular memory.
You do not at all get around this difficulty by suggesting the idea that a memory or a piece of learned information is scattered in multiple locations across the brain. The difficulty is explaining instantaneous recall. If a brain has to search scattered storage locations in the brain, that would not be any easier than finding a single storage location. We would then have the same problem: how is it that those exact locations can instantly be found? Similarly, if a family is somewhere in New York City, and you don't know their address, you won't be able to find the family very quickly; and it's not going to be any easier if the family is scattered across three different apartments.
You also do not at all get around this difficulty by suggesting the idea that the brain reads all of its information each time a memory is retrieved. For one thing, such an idea does not correspond to human experience. If I hear a name, I recall only what I have learned about that name, and do not at all have some experience of recalling or reading some huge amount of information. Moreover, the idea of the brain reading all of its stored information (rather than one tiny spot) just worsens the problem of explaining how instantaneous recall can occur. Instantaneous recall could never happen if a brain was reading all of a large amount of information stored in it, or even a tenth of such information.
Problem #2: A Brain Would Never Know Where to Write a Memory
Now let us consider a separate problem regarding the idea that brains store memories: the problem that a brain could apparently never derive an exact suitable specific location at which a new memory should be written.
With certain types of systems, there is no problem about where to write a new piece of information. Consider a diary. A diary typically consists of dated pages. So it's always obvious where you should be writing when you make a diary entry: in the page that has the name of today's date. It is also rather obvious in a student's notebook where new information should be written: at the end of the last place where something was written.
But a brain is not at all like a diary or a notebook. There are no date-marked places to put information acquired on some particular date. And given the organization of the brain, there is nothing like some place corresponding to the first blank page of a notebook. So, if a brain were to be writing some new information acquired on a particular day, how could the brain figure out or derive some appropriate position to write at?
We will not get any insight into this question by considering how a computer stores data. Imagine I open an application, and write some text. I then try to save my information as a particular file. How does the computer figure out where on the computer to store this information? What seems to happen is that the software application uses the computer's operating system to save the file. The operating system is a core set of software routines used for common tasks such as saving files. If we were to delve into the software code of the operating system, we would probably find that the operating system code searches for a random block of free data on the hard drive, a block with enough space to store the data.
For example, suppose I open the “Notepad” application, and type 100 words. When I choose File/Save from the menu, the application calls some software (probably operating system software) that looks for a random position on the disk with enough space to write 100 words. Random selection is very easy for a computer (for example, it's easy for some sofware routine to pick a random number between 1 and 100).
Here is the type of algorithm that an operating system might use to save data at a random free location:
- Pick a random position
on the disk.
- Scan ahead X bytes to
make sure that the next X bytes are free space on which nothing is
written (where X is the amount of data to write).
- If the next X bytes are
free disk space, write the data to be written at the random
- If any of the next X
bytes are not free disk space, go back to step (1).
Can we imagine that something like this goes on in the brain, even though we have no mental experience of any such logic or calculation going on when we form a new memory? It does not seem that something like this could be occurring in the brain. The brain has nothing like the operating system in a computer. A brain cannot secretly be doing logic like the logic above to determine where to write a memory.
We may consider the simple matter of picking a random position in the brain to write a memory. For a conscious agent, it is very easy to pick a random position. But it would seem to be impossible for a brain to pick a random position in itself without any conscious choice being made by a mind.
There are certain physical arrangements that can kind of guarantee a random positioning effect. For example, if I throw a small ball on a large grate covering a hole, such an arrangement will make it likely that the ball will fall through one of the holes in the grate, with the ball going through a random hole. But there seems to be no physical arrangement in the brain by which some random position in it could be selected as the place to write a memory.
One possibility is the possibility of a cursor. In a word processing document, a cursor is blinking position marker indicating the current writing position. We can imagine something similar in a brain. There could be something like a “moveable write unit.” When a memory is stored using the write unit, the write unit could write wherever in the brain it was located. The write unit could move along as it wrote. Under such a system, there would be no need for a brain to be selecting a random position to write at. The brain would simply write at wherever brain position the write cursor was located at.
However, there is no sign of such a cursor or movable write unit in the brain. Other than electricity and chemicals and blood moving around in the brain, there are no moving parts in the brain. Electricity and chemicals are evenly distributed in the brain, and there is no concentration of electricity or chemicals that could be anything like a memory cursor or a moving write unit. The human brain bears no resemblance to a system for storing a particular memory in one specific spot. Similarly, the human body bears no resemblance to a system for storing the nutrients from a meal in only one specific spot of the body.
A scientist may claim that when some new memory is acquired, that memory is stored in some exact tiny spot of the brain. But such a person could never give a credible answer to the question: why would such a memory have been stored in that exact tiny spot rather than any of a million other tiny locations in the brain?
Faced with such difficulties, someone may throw up his hands and say, "There must be some way by which some particular spot in the brain becomes the current spot where you store what you are learning right now." To this I say: no, there isn't any such thing. The difficulties I mention are only two of a host of prohibitive difficulties involved in the idea of a brain storing a memory. Others discussed at great length here include the lack of any known information reading mechanism in a brain, the lack of any known information writing mechanism in a brain, the complete lack of any credible theory by which conceptual and episodic information could be translated into neural states or synapse states, and the lack of any credible theory of how memories could be stored in a brain for decades given high molecular turnover such as the very rapid protein turnoever in synapses. The way to overcome such difficulties is to abandon the never-proven claim that memories are stored in brains, and to move to the idea that memory must be a spiritual facility.