We often have the experience of recollecting a memory.
Typically it will not be a single memory,
but a set of interrelated memories.
Reconstructing it, we might remember the colours, the sound,
something the person said, and the way it made you feel.
The brain's ability to collect, connect and create a mosaic,
from these milli second impressions, is the very basis of memory.
By extension it is the basis of our self.
This is not just metaphysical poetics.
Every sensory experience, triggers changes in the molecules of our neurons.
It reshapes the way we connect to one another.
The brain is literally made of memories.
Memories constantly remake our brain.
Recent findings indicate that memory exists,
because our brain's molecules, cells and synapses can tell time.
Defining memory is about as difficult as defining time.
In general terms memory is a change to a system,
that alters the way that the system works in the future.
A typical memory is really just a reactivation of connections,
between different parts of our brain,
which was active at some previous time.
All animals, -even many single celled organisms -,
possesses some kind of ability to learn from the past.
It may be difficult to compare a sea slug, with a human.
But both have neurons, and sea slugs form something close to memories.
If we pinch a sea slug in its gills, it will retract them faster,
the next time our cruel fingers touches it.
Scientists found synapse collections that strengthen when the sea slug learns to suck in its gills.
They know the molecules that causes this change.
Remarkably human neurons have similar molecules.
How does this relate to our favourite memory?
What is unique about it, is that the neurons connect to thousands of other neurons,
each very specifically.
These connections form a network.
The specific connections, in the synapses, can be adjusted with stronger or weaker signals.
So, every experience, -every pinch to the gills- has the potential to reroute the relative strengths,
of all the neuronal connections.
The molecules or even the synapses they control do not constitute memory.
If we dig in, to the molecules the states of ion channels synapses,
in the whole network of neurons, there is no one place in the brain where memories are stored.
This is because for property called plasticity, the feature of neurons that memorise.
The memory is the system itself.
There is evidence of memory making through out the tree of life.
Even creatures with no nervous system can have some kind of memory.
Scientists have trained bacteria to anticipate a flash of light.
Primitive memories like the sea slug response, are advantageous on a evolutionary scale.
It allows an organism to integrate something from its past, into the future,
and respond to new challenges.
Human memories, -even the most precious- begin at a very granular scale.
Our mother's face began as a barrage of photons on our retina,
which sent a signal to our visual cortex.
When we hear her voice, the auditory cortex transforms the sound waves into electrical signals.
Hormones layer the experience with cortex, -the person makes you feel good- .
These and the virtually infinite number of other inputs cascade across our brain.
The neurons, their attendant molecules, and resultant synapses encode all this related perturbations,
in terms of the relative time they occurred.
They package the whole experience with a so called time window.
No memory exists by itself.
Brains breakdown experience into multiple timescales, experienced simultaneously.
For example, sound is broken down into different frequencies perceived simultaneously .
This is a nested system, with individual memories existing within multiple time windows, of varying lengths.
Time windows include every part of the memory, including molecular exchange of information,
that are invisible at the scale, we actually perceive the event we are remembering.
We are far from complete understanding of how memory works.
In an ideal world we would be able to trace the behaviour of each individual neuron in time.
At the moment projects like Human Connectome represent the cutting edge.
They are still working on a complete picture of the brain, at a standstill.
Like memory itself, putting the project into motion, is all a matter of time.