 Hi, my name is Andrea and in this video I will introduce some concepts about the neuroscience of memory and especially memory loss or forgetting. In this first part I would like to talk about how people started thinking about what could be the biological substrate of memory and how ideas developed at the beginning of the discipline. I believe it is extremely important to deliver the message here that ideas and concepts do not come from thin air. All the discoveries in science were primed by the ideas floating in the discipline at the time of the discovery. As a society we define the course of science by defining the questions that we ask and are interested about and this is a very good example of it. I would like to begin with a quote. It's from the Spanish film director Luis Buñuel and it says, you have to begin to lose your memory if only in bits and pieces to realize that memory is what makes our lives. Life without memory is no life at all. Our memory is our coherence, our reason, our feeling, even our action. Without it we are nothing. I think this quote summarizes extremely well the relevance of memory for the sense of self and some of the things that we will discuss in this video. So what is memory? The first dichotomy that interested philosophers was is it something physical, something we can measure or is it something that is out of our reach? Since we cannot really do much for the abstract hypothesis it was soon discarded towards looking for the origin of a physical measure of memory. During some time it was believed that memory was stored all over the body, however scientists soon realized that the brain was somehow crucial to memory and the identity. The most straightforward thought about how does the brain store memory is, well memory must be represented by something that's created and stored there. So the more the memories the bigger the brain. The initial ideas were guided towards the notion that a new memory would require new cells or something new to be created. There is no much growth going on in the brain since a human turns 10 years of age approximately, but this doesn't mean that everything is settled. The brains of differently aged people who had certainly a different amount of memories puzzle the scientists. How could it be that the brain size did not equal brain storage capacity? We do accumulate an increasing number of memories, thus those memories are not stored by creating new cells but by modifying the existing ones. At this point philosophers, neurologists and other scholars started to be very interested in defending how does the brain record a memory. It was so proposed that the brain somehow manages to associate series of events, but it was still unclear how this association could take place in the brain matter. At this point it was still believed that the brain was a continuous web of intricate connections like a ball of wool. It was believed that the neurons, the brain cells, were physically connected to each other, something called the reticular theory. A notable observation was made by the Spanish scientist Santiago Ramon y Cajal around the end of the 19th century. Cajal spent most of his life glued to his chair looked into stained chicken brains and he was amazed at what he saw. What he saw was that the cells in the brain were not all connected to each other as everyone thought, but there were little spaces between them. These spaces meant that the cells did not really touch each other. This was named the neuron doctrine. After this scientists started wondering what could be happening in those spaces between neurons. They started proposing that those connections were the key to identify a memory. A Polish neuropsychologist defined neuronal plasticity as the ability of neurons to be altered by experience. This is a very important concept as it implies that the brain is both very stable to be able to store information for a lifetime, but at the same very malleable to be able to build and change these pieces of information. Not long after, a famous Canadian psychologist Donald Hub set the basis for what is called synaptic theory, which described how these associations could happen at the neuronal level. In a famous book Passets, he describes, when an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic chains takes place in one or both cells, such does age efficiency as one of the cells firing B is increased. This has been lately simplified with the catchy neurons that fire together, while together. Lastly, scientists managed to describe for the first time the phenomenon of long lasting potentiation, neuronal plasticity induced in the laboratory. This opened a new world for scientists which started using these techniques to study in depth this phenomenon and that has led us to today. But why is this discovery so important and what does potentiation mean at all? This is something we will cover in the next part. Thank you for your attention.