Memories
Last night I drove after three months of cycling. I took some relatives to a small restaurant on the hills surrounding Bologna. I ate quite a lot, as usuall, and we had a nice time together.
By the way, the journey from home to the place wasn't that nice, since, although I like driving VERY much, a small, dark, hill road is not what you would call the easiest one for reviewing your driving skills. Nevertheless, I didn't have any trouble: I was just a little bit worried in the beginning.
It's hard to define what memory actually is: maybe the faculty of recalling facts or recognizing episodes of the past is the clearest.
Certainly, finding out all the cerebral pathaways that deal with this faculty is one of the toughest tasks of today's neuroscientists.
However, nowadays we know something.
First of all, we can define three (but there are different classifications) memories: short-term, long-term implicit and explicit memory.
Short-term memory can be called working memory as well. This second, more modern name is used to underline the functions of this kind of memory. A short-term memory, in fact, helps us every time a particular task needs a quick storage and manipulation of information/data (i.e. remembering addends for a sum and calculating the result).
Studies on monkeys and patients with brain injuries have revealed that some areas of the premotor cortex show an increases activity during processes which require the use of working memory.
When it comes to long-term memories, things get more complicated and unknown. There are five regions certainly involved: one is subcortical ( the amygdala) and the others are in the temporal cortex (namely, enthorinal, perirhinal and parahippocampal cortex, hippocampus).
Explicit memory is also called declarative memory: basically, it's when we are aware of knowing something (i.e. where we live).
Amygdala has a central role in linking memories and emotions together.
Hippocampus is nicknamed "teacher", because of its paramount importance for declarative memory. Its bidirectional connections with all the cortices explain why it plays a key role in explicit memory.
Interestingly, in the hippocampus there are staminal neurons.
Perirhinal cortex makes us remember, in a nutshell, objects, while parahippocampal cortex is linked to visuospatial memory. Both have the same bidirectional links to all the cortices we described for the hippocampus.
These two regions send information to the enthorinal cortex, which processes the inputs. Enthorinal cortex is linked to the hippocampus too and provides a huge number of inputs for it.
Implicit memory is also known as procedural memory: we know how to do something, but we are just not aware of it. And that's the link between yesterday's driving after a long time and memory. Implicit memory is what helps us doing many things without, literally, thinking about what we are doing. For example, if we constantly had to think about how to move our legs while cycling, we would be probably fall down very quickly.
The scheme is quite simple: all cortices have connections with basal ganglia but not the way back. Hence, we can't be aware of the process.
Basal nuclei (another name for basal ganglia) receive stimuli also from the substantia nigra.
Inputs travels from basal nuclei to ventral thalmus and, finally, reach the premotor and motor cortex.
