This post was written on Thu, 25 Sep 2003.
Human Memory :
The cells responsible for brain processes and memory are called neurons. Neurons have specialized projections called dendrites and axons. Dendrites bring information to the cell and the axons take information away from the cell. So Neurons are connected to each other through these projections. A neuron can have several dendrites but it usually has only one axon. But fear not! At the end of the axon there are several terminals. These terminals can be connected to several other neurons. So our nervous system is made of neurons connected to each other through their projections. Each of these connections is called a synapse. There are a HUGE number of synapses in the brain. In a new born child each neuton in the cortex has about 2500 synapses!! And the human brain has about 100 billion neurons…… Imagine that!!
See the above image. THis shows a neuron with its dendrites, axon and terminals at the end of the axon. Now see the image below.This shows the synapses between the dendrites of one neuron and the axon of another.
And the number of connections is ot fixed. The human brain is very “plastic”. It can grow/reduce based on your needs. A new born child has about 2500 synapses per neuron. By the time the child is 2-3 years old this grows to 15000 synapses per neuron!! The child is curious.
He wants to learn. And tragically, the number of synapses per neuron in an adult brain is about 1/2 that of a child. He is no longer curious….
He wants to read only about his profession. He is too busy impressing people to be able to think any orignal thoughts. What he does
not understand he attributes to God :-). But what is happening here????!!! Do the number of synapses decrease? Does this mean that the brain is
deleting synapses? Yes! This is called synaptic pruning. Like a gardener, the brain removes the synapses that are not needed….But how is that
decided? If a synapse has not been used for a long time and does not have an emotional significance then it is removed. Snip! snip! and there
goes your knowledge. When was the second battle of Panipat fought? Who defeated whom?? Forgot? You got snipped by your own brain sweetie.
So how do we learn something new? When we experience something a set of neurons activates(“fires”) together. They form a connection
between each other. If the experience is very exciting then the neurons fire more intensely and the connections between them become stronger.
The next time a similar event occurs there is a strong possibility that the same neurons will fire again and you will remember! So the whole event is coded in these inter neural connections. If you experience only one aspect of an old memory you might experience the whole thing again because the neurons associated with that intense memory will fire together again. You might have noticed that a certain song, a certain taste will take you back to a time when you experienced it first. But this happens only if the orignal experience was intense enough to produce that kind of firing of neurons. I know a set of songs that take me back to those old times….and a certain taste of coffee that will take back to those exam days and I will remember not only the coffee but allso the exams and the books… the whole experience.
That is why to remember something that we have forgotten you can try and think about a related thing. So when you think about something related the neuron for the memory that you want to remember may fire with it and you may remember.
How do neurons communicate with each other? This is an electro chemical process. An electric signal travels down an axon and when it reaches the terminal a set of chemicals get released which travel across the synapse to the dendrites of the connected neuron. This causes the electric signal to travel from the dendrites of the new neuron to its cell centre etc.
A temporary memory is a simpler connection. A loop: a neuron X is connected to Y and Y is connected to X. After some time the connection is not there anymore. Only if your brain feels the need will this be connected to the larger permanent memory.
A few other facts about memory:
Some of our most emotional memories are triggered by smell!!
- Excitement enhanhances memory formation and depression inhibits it.
The human brain has a special area to store faces. That is why sometimes you will recognize a face but not be able to recall his name.
You have more memories than you can remember. The neurons may be there but you are able to reach them because of a lack of connections to them. An isolated incident/experience may spark it again.
” Lulled in the countless chambers of the brain,
Our thoughts are linked by many a hidden chain
Awake but one, and lo, what myriads rise” (Alexander Pope)
Enjoy this video by VS Ramachandran :
Go, wondrous creature! mount where Science guides:
Go, measure earth, weigh air, and state the tides:
Instruct the planets in what orbs to run,
Correct old time and regulate the Sun;