Involuntary memory is the serendipitous recollection of past events through an unexpected stimulus. In Proust’s novel* it is famously the eating of a Madeline dipped in tea which triggers the protagonist’s memory.
Current thinking on the structure of the brain is that it operates somewhat like a watershed. Instead of rain falling on hills, carving a stream which becomes a river and flows to a meeting with the sea, we have a set of stimuli which react in the brain, following established links and connections to come to a certain conclusion.
When we have a particularly happy event, our levels of neurotransmitters are high. Patterns are laid down by Dopamine, Seratonin and Norepinephrine in our brain. These patterns are associated with a pleasurable experience (or sometimes with a traumatic one).
The patterns act like the watershed of a river. A little rain falls on one side of a hill in County Cavan, and it will flow to the sea via the Shannon River. With a small gust of wind that rain falls on the other side of the hill. The water will enter Lough Erne and reach the sea at Sligo bay. Once the watershed is established that rain can go nowhere else but down the established flow.
In the same way the smell of cookies in the oven may trigger memories of your grandmother. A particular floor polish smell may bring back the memory of visiting your father at work. A certain taste combination may open up a memory of a very special night of moonlight and romance. One neurotransmitter sets off another and another in sequence until the memory is fully formed.
Involuntary memory is as good as it gets!
Sonnet XXX; by William Shakespeare
When to the sessions of sweet silent thought
I summon up remembrance of things past,
I sigh the lack of many a thing I sought,
And with old woes new wail my dear time’s waste:
Then can I drown an eye, unused to flow,
For precious friends hid in death’s dateless night,
And weep afresh love’s long since cancelled woe,
And moan the expense of many a vanished sight:
Then can I grieve at grievances foregone,
And heavily from woe to woe tell o’er
The sad account of fore-bemoaned moan,
Which I new pay as if not paid before.
But if the while I think on thee, dear friend,
All losses are restor’d and sorrows end.