Tuesday, November 20, 2007

Medicine: The power of memories

Yesterday I tried to make a tuna fish salad again, but with minimal ingredients this time; I didn't have cucumbers nor peppers! Anyway, one of the most amazing things just happened while I was squeezing a lemon over the freshly cut onion - my nose caught the scent which reminded me of souvlakia-sheftalia (σουβλάκια-σιεφταλιά, ражњићи), which I haven't tasted for almost two years!
Souvlakia-sheftalia is a Greek/Cypriot traditional specialty usually served with salad or half an onion and half a lemon, all packed in a nice pocket-shaped bread (pitta - yes double 't'). Memories can be quite amazing sometimes.

Now on to the real part: Memories! Your memories aren't but chemicals, nicely organised in neuron, waiting to be released. When the human nose catches a familiar smell within a respected range, the smell could be connected to some old memories, in my case, FOOD! I believe the term for this occasion is "Olfaction memory". But how is this connected?

I won't go into many details, but here's a brief road-map: The human nervous system has been divided into two big parts, the central (CNS) and the peripheral nervous system (here is a short summary of the NS stucture I made). CNS consists of the brain and the spinal cord.
Somewhere in your brain, there's a Hippocampus is one of the main parts of the Limbic System, controlling emotion expression and memory. The amygdala play a big role for the expression of emotions such as sadness, need to reward/congratulate or fear, anger, etc. Don't forget that emotions can often be triggered by a smell - like the sweet, sweet smell of souvlakia! Argh, now I'm hungry again.

Anyway, the memory part is controlled mainly by hippocampus (thank God there's Wikipedia to show where it is, so I'll be able to keep this short). Its name is given from its shape - in greek (or latin for that matter), ιππόκαμπος means sea-horse. If you damage this baby you'll end up either losing your ability to memorise new things (anterograde amnesia) and probably access to memory before the damage (retrograde amnesia). At patients that suffer from Alzheimer's disease, the hippocampus is probably one of the primary parts of the brain that is damaged.
Before you start nagging that this is a huge and boring post, there is one more thing I'd like you to see, the rhinencephalon and the olfactory tract. Some thousands (correct me if I'm wrong) of olfactory neurons, that hang on the top border of your nose (ethmoid bone), send signals through the olfactory tract all the way to the olfactory or piriform cortex. As you can see, it is tightly connected to the Limbic system, hence the connection between the senses and emotion expression or memory recall. Each sniff you take is "encoded" to several bits of local depolarisations, if they're enough they're added up and create an action potential and finally sent towards your brain, an impulse to the limbic system in our case. Although the neurons between the limbic system parts go into an loop, the system has several cut-points, points where the axons are connected with other neurons, therefore points where new signals take place in the loop. From there, the amygdala send direct orders to the brain to bring me a sense of euphoria or satisfaction and the hippocampus retrieves the information from the long-term memory "database" about the specific smell.

Imagine this post as a backstage pass; not to a Madonna concert, but to one of your many body functions :-)
You disagree on anything of the above? State your opinion by writing a comment.

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