The average adult human brain is estimated to have 1 quadrillion synapses.
Scientist proclaim that each synaptic bond is the equivalent of one bit (binary 0 or 1) of data, since they claim that all long term memory is physically encoded in the brain through the strengthening of synaptic bonds. This mechanism of memory encoding as a process of synapse bond strengthening is called long–term potentiation (LTP). In other words, a bond that is NOT under the effects of LTP could be considered to be a binary bit in the zero position, while a bond that is under the effects of LTP could be considered to be in the one position.
To demonstrate why it is logically impossible for such bond strengthening to account for all encoded memory, we just have to look at what we know about computers once again.
The equivalent amount of bytes (8 bits or one letter character) in a computer amounts to 125 terabytes (125,000,000,000,000 bytes). So in effect, the neuroscientists who think that all memory is physically encoded in the brain must believe that the human mind can store at most 125 terabytes of data.
An hour of compressed HD video is roughly 4 gigabytes of data, so the human mind could hold (according to this theory) roughly 31,250 hours of HD video.
This might sound like a lot, but consider that only amounts to about 3.5 years worth of HD video. Of course, human memory includes smells, tastes, touches, 3 dimensions, and host of other sensory and emotional inputs that HD video fails to capture.
I also want to point out that I am being massively liberal with my interpretation of the number of bytes that the human mind could possibly store if this is indeed how memory is physically encoded into the human mind. Most psychology text books put the number faaaaaar below that, at around a terabyte. EEG studies of the brain show that most long term memory and spatial navigation activity is centered around the hippocampus with smaller activations located in other areas of the brain. Scientists surmise that memory “moves” from the hippocampus to other areas of the brain (through an unknown mechanism) over time.
Given that, how do we explain cases such as this? Some people (granted very few, but only one case is sufficient to prove my point) have the clear ability to recall nearly every day of their adult life in practically perfect detail. That amount of information is enormously larger than 125 terabytes of data. Also, people who undergo near death experiences often relate stories of undergoing a life review where they can see a perfect holographic projection of their entire life, which includes not only all the sensory information, but also all the emotional information of the events being reviewed.
Now before I go further, I should point out some interesting findings about long term memory. Scientists have been able to isolate a specific protein kinase (PKMζ) that keeps up the long term synaptic bond strengthening (LTP), and if they induce a protein inhibitor that blocks the production of this specific protein kinase, they can induce the loss of long term memories in lab animals.
A stunning finding to be sure. This means scientists, in theory, have a way to wipe out the long term memories of the human mind through administering a drug that blocks the production of PKMζ.
Thus, we know that LTP and the protein kinase PKMζ play a role in the ability to recall and store long term memories in lab animals (and presumably humans).
Is this proof that memory is retained in state in the brain through LTP?
I think at most what we could say is that LTP might represent a reference variable to a memory (that is to say, the brain might physically encode how to recall a memory into the physical consciousness, but not the actual memory itself). Scientists have zero understanding of how a memory is recalled and what causes it to be recalled.
Since we know the amount of data people can recall is more than the amount of data that is physically capable of being stored through LTP , the actual storage of that data must still be “off-site” so to speak.
Further, if it can be demonstrated that the exact same synapse undergoes LTP for the recall of two totally different memories, it should be clear that state is not maintained in a classical sense. For this would be the equivalent of a hard drive accessing the storage location of a tax statement and coming back with a document on healthy eating.
I also want to stress that there are constant state changes going on all over the brain all the time. New cells come into existence, old cells die, old connections fade and are reformed, etc.. etc.. etc.. which further confounds this notion that long term memory is entirely encoded in the brain by a physical mechanism.
Further, we don’t know what the actual effects of inhibiting PKMζ production would do in humans, we only know that lab rats display signs of forgetting things they have learned in the past when their production of PKMζ is inhibited. The actions of the rats could be due to them undergoing some kind of experience other than memory loss. We can’t tell with total certainty because obviously it would be incredibly dangerous and unethical to test this on a human subject if indeed it does wipe out access to long term memories.
PKMζ Maintains Spatial, Instrumental, and Classically Conditioned Long-Term Memories
PKMζ Inhibition Reverses Learning-Induced Increases in Hippocampal Synaptic Strength and Memory during Trace Eyeblink Conditioning
-The term CR refers to conditioned responses
-Tetanization refers to the use of electric shocks to induce a state of LTP in a synapse artificially, typically to test how learning is effected if a huge number of synapses are already in an artificially induced state of LTP (leaving less available for natural processes to use.)
Wiki entry on Pam Reynolds