WHAT HAPPENS IN OUR BRAIN WHEN WE LEARN SOMETHING? AN INTRODUCTION TO COGNITIVE AND CELLULAR NEUROSCIENCE
In the fourth century before Christ, the Greek philosopher Aristotle thought that the heart was the most important organ of our body and the essential center for learning and mnestic processes. Today we know that learning and memorizing are cerebral and not cardiac functions, but there are remains of Aristotle’s vision in the expressions used to say “memorize something” in English, French and Arabic, respectively “learn by heart”, “apprendre par coeur” and “hafiza a’n zahri kalb”. The first experimental studies on memory were conducted at the end of the nineteenth century by the German psychologist Hermann Ebbinghaus, who was used to write long wordlists and memorize them in order to record the minutes he took to memorize new information and to draw both the learning and the forgetting curve. His observations were deepen fifty years later by the American psychologist George Armitage Miller, who discovered that “seven plus or minus two” is the magic number of items that people can memorize when a list of letters, words or numbers is showed for a short time during a memory performance task. These and other investigations on timing and size memory allow to differentiate short-term memory, which is the ability of remembering a small amount of information for a short period of time, and long-term memory, that is the same capacity but over longer periods of time. In 1957, the British neuropsychologist Brenda Milner described the mnestic impairments of Henry Molaison (H.M.), a man suffering from a severe amnesia due to a side-effect of a brain surgery. However, neuropsychological tests revealed that some kinds of memory were still present in H.M. and these evidence supported the conclusion that different types of memories exist (declarative vs. procedural, episodic vs. semantic) and are stored in different parts of the brain, thus leading to the definition of several models for learning and memory. The behavioral and anatomical studies on H.M. highlighted the key role of a cerebral structure called hippocampus, a part of which have been removed during the neurological surgery. In the Sixties, the investigation of mnestic processes in a sea slug called Aplysia californica by the future Nobel Laureate Eric Richard Kandel shed light on the cellular and molecular basis of memory in an animal model. In recent years, the development of neuroimaging techniques, namely scientific tools that allow us to see what happens inside the brain during a learning task, acted as propelling thrust to the investigation of neural networks, making brain science an even rapid-growing field of research. This paper addresses the most important issues on learning and memory: it begins with an historical review and than focuses on what happens in our brain when we learn something, analyzing the most recent findings on cognitive and cellular neuroscience.