How are data, like found on computers, carried and stored? Does our own memory work in the same way?
The first major difference between computer and brain memories concerns the physical changes that occur when a memory is stored. Computers store memories by switching the state of some storage medium between two possible configurations. For example, the polarity of a magnetized region of hard drive can be set in one of two directions, representing the zeros and ones of the binary encoding of digital data. In brains, a variety of different physical changes are associated with the storage of memories. During memory formation, connections between brain cells can be created, removed, strengthened, or weakened. Within individual brain cells, memory formation also involves changes in the production, localization, and chemical modification of proteins and other molecules.
The second major difference between computer and brain memories is the way in which the physical changes described above are used to recall the stored memory. If a computer is used to look up stored information, such as a phone number, it finds the location on the storage medium where it previously wrote this information and then reads the binary data stored there, for example, by measuring the magnetic field at a specific hard drive location. Brains, in contrast, do not recall memories by directly measuring whether or not the physical changes described previously have occurred. Instead, these physical changes alter signaling within and between brain cells. For instance, changes in the connections between two brain cells alter how activity in one cell influences the activity of the other. Changes in protein expression within a single brain cell can influence how robustly the cell responds to inputs from other brain cells. These memory-related changes to brain signaling influence the dynamics of brain activity by evoking memory recollection.
How exactly memory recall happens remains largely unknown, although an abundance of ongoing research has provided much insight into this question. One prominent hypothesis is that memory recall occurs when a specific set of brain cells, which originally represented the perceptual experience that was stored in memory, becomes reactivated at a later time. For example, when I pick up a rose to smell it, one group (group A) of cells in my brain becomes active to represent the flower's fragrance, another group (group B) becomes active to represent the rose's appearance, and yet another group (group C) becomes active to represent the feeling of the thorny stem (ouch!). As these brain cells are activated, direct and/or indirect connections between the three groups are formed and strengthened. So, what happens when I next approach a rose? The rose's smell and visual appearance activate cells in groups A and B. Because my previous experience caused strong connections to be formed between cells in groups A, B, and C, the activity in the cells in groups A and B causes the cells in group C to become active simultaneously. Because the cells in group C represent the feeling of the thorny stem, I remember my previous painful experience before I repeat the mistake of picking up the rose.