Is it theoretically possible for our memory to become full to the point where it can no longer record information?
Geoffrey Clark
Douglas, Isle of Man, UK
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I can say that at 71 years of age my memory is indeed full of all sorts of stuff, but I can’t remember what I had for breakfast! I think my brain is indeed full.
David Nye
Eau Claire, Wisconsin, US
No. Memory is encoded in the brain by networks of neurons, whose interconnections – called synapses – have been altered so that they are linked together in a way that represents the memory.
The memory of a red apple is represented by a group of neurons that respond to the colour red, connected to a group that respond to the round shape, and another group that respond to the taste and so on. The activation of the network of neurons encoding a memory causes it to appear in the mind. The same groups of neurons may be reused in many memories, so the two groups representing round and red will resonate when we think of or see either an apple or a red ball.
There are an estimated 86 billion neurons in the human brain – not all of which are used for memories – and 100 to 200 trillion synapses.
That is a lot of storage, but even if you have completely connected up all of the available neurons and filled your brain with memories, you will be able to add new ones by altering existing connections and repurposing your neuron networks, although that might cause you to lose some weaker memories.
Graham Martin
Wellington, New Zealand
A common clinical test is to give people a series of numbers, then ask them to repeat them in reverse order. Most of us can only manage this for a series of four numbers, and a few people can manage five.
Anthony Woodward
Portland, Oregon, US
Sherlock Holmes thought that his memory had limits. To the astonishment of Dr. Watson at Holmes’s ignorance of the Copernican theory, he responded “I consider that a man’s brain originally is like a little empty attic”, which he didn’t wish to fill up with irrelevant data. But the question of whether Holmes was right is bedevilled by our ignorance of how memories are formed.
Dictionaries define memory as the ability to store and retrieve information. This faculty rests in the brain. The information is gathered largely through sensory systems, but we can remember dreams and even remember having memories that seem to be secondary regurgitations of primary memories.
The consolidation of long-term memory involves permanent and repeatedly reinforced changes in the proteins of certain neurons and in the function of their synapses. The astronomical numbers of neurons and synapses that are present in the brain suggest that there will always be room for more memories.
We can answer the question “How much water can I put in my bathtub?” because we know the total volume of the container and have a unit of volume for water. But we are ignorant of the container of memories and we have no unit of memory. Therefore, we cannot answer the question “How much can I put in my memory?”
Has a professional pianist ever hesitated to add another sonata to their repertoire, or an actor ever refused another play, because they have already filled their memory?
There seems to be no evidence of any limit to human memory for a healthy brain. However, the situation may be different for a brain affected by a condition such as Alzheimer’s disease.
Hillary Shaw
Newport, Shropshire, UK
Our memory probably can’t become full because our use of symbols and images facilitates what we might call “partial memory hierarchies”.
I don’t need to remember the location of every town and city in the world, or the translation of every English word into French, I just need to remember where my atlas and French dictionary are. I also need to remember what those 26 squiggly shapes mean when strung in different sequences, but I don’t need to know all of the valid sequences.
Going one hierarchical stage up, I just need to remember where my computer is and how to use the internet, or remember where the nearest library is, to have access to an even wider range of “memories” laid down outside my brain. The Dewey Decimal System means I don’t even have to remember what books are found where in that library. This hierarchy appears to have no fixed limits to its capacity.
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