TOP 5 DEEP SEA CREATURES
5 July 2025
Top 5 Creatures of the Deep The deep sea is a dark and difficult place to live, but the creatures
Where in our brains are memories stored, and in what form? How are memories created? Why can I remember some events from years ago, but hardly anything from this morning? These are all questions about ‘the biological basis of memory’: about how the biology of our brains enables us to remember past events.
The human brain is made up of about 100,000,000,000 specialist cells called neurons, and each neuron is an unusual cell in two ways:
● When stimulated, a surge of electric current passes across its membrane. This tiny electric shock is called an action potential.
● It has lots of branches, each of which makes contact with another neuron at a synapse. Here, messages pass from one cell to another in the form of a chemical called a neurotransmitter.
It is in the form of these electric currents, and the connections between neurons at synapses, that all of our memories are stored.
We have three very different sorts of memory:
Sensory memory lasts for less than a second. It is the fleeting memory of things we have just seen, or sounds we have just heard and it decays very fast. For example, if shown a series of 12 letters (like those in the red box) for a fraction of a second, someone can ‘read off’ one of the rows from their sensory memory, but this memory has decayed before they get to a second row. Try it now – look at the box below for the length of one breath, then try to write down the sequence of letters as they appeared in the box. How many can you remember?
Short-term memory lasts for up to a minute, but contains fewer than ten items. Unlike sensory memory, this sort of memory can be retained by rehearsal: by paying attention and repeating the information to yourself over and over again. This is how we remember telephone numbers long enough to write them down, for example.
Long-term memory lasts much longer – up to a whole lifetime in fact – and has a huge capacity. Short-term memories are converted into long-term ones by attention and rehearsal (as when you learn lists of facts), or if they are emotionally powerful (as when you witness a frightening event like a car accident, or a happy event like blowing out birthday candles).
When you see something, light from an object enters your eye. The information in this light is encoded (changed in form) into a pattern of action potentials by the retina at the back of your eye. These action potentials travel down the optic nerve to your brain. How you remember the seen object then depends upon what happens in the brain once the action potentials arrive:
● Your sensory memory only lasts while the action potentials are ‘firing’ in the brain. These die down very soon.
● Your short-term memory results from supplies of neurotransmitter running short in some neurons but not others. After a few seconds, new supplies of neurotransmitter are created, the pattern of these shortages fades, and your memory of the object fades with it.
● Your long-term memory, formed by rehearsal or emotional power, comes from the strengthening of some synapses between different neurons. New proteins are formed which make these links between neurons permanent rather than just temporary. As there are trillions of possible synapses, the number of possible new linkages is almost infinite. This is why you are able to learn and remember such a lot of material.
The brain has many different regions, each of which is specialised to do a particular job. So, for example, the part of the brain where you ‘see’ is the visual cortex right at the back.
Two small parts of the brain are very important in the storage of memories.
● The minute hippocampus is where short-term memories are converted into long-term ones for eventual storage elsewhere. We know this because someone with a damaged hippocampus becomes unable to form new memories about events they experience. The hippocampus is one of the first regions of the brain to be damaged during Alzheimer’s disease, a disease involving extreme forgetfulness. So it is also important for bringing stored memories back into consciousness again.
● The equally small amygdala ensures that emotionally powerful events are remembered long term. If damaged, frightening or happy events are no more likely to be remembered than normal ones.
You might ask how biologists have found out about memory and the brain. Three lines of research are especially important:
● Noting the effects of damage to various parts of the brain. Damage to different parts results in different changes to memory function, as in damage to the hippocampus and the amygdala above.
● Investigating the effect of stimulating different parts of the brain with small electric shocks. As these shocks imitate action potentials, they ‘switch on’ different parts of the brain so that their activity can be observed.
● Injection of chemicals, especially those imitating or affecting neurotransmitters, into different parts of the brain. These switch synapses on or off, and their actions can once again be observed.
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Words: AQUILA Team Illustration: Hi-lo Piccolo
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