Brain

The brain is a pinkish-grey, wrinkled organ that fills the skull — looking, for all the world, like a huge walnut. It is hard to believe, from its appearance, that this ugly lump of jelly contains the mechanisms of thought, perception, will, and consciousness, that it is the seat of our personality. Its 100,000 million nerve cells, each with an average of 100,00 connections from other neurons, makes the human brain the most complicated and least understood object in the known universe. The vertebrate brain is the large anterior portion of the central nervous system . The "cranial vault" of the skull encases the brain in most vertebrates. In invertebrates, the enlarged and specialized anterior ganglion of the central nervous system is often referred to as a brain, although not all scientists regard it as a true brain.

Memory loss

Memory loss (amnesia) is unusual forgetfulness. You may not be able to remember new events, recall one or more memories of the past, or both. Normal aging may cause some forgetfullness. It's normal to have some trouble learning new material, or needing more time to remember it.
However, normal aging does NOT lead to dramatic memory loss. Such memory loss is due to other diseases. Sometimes, memory loss may be seen with depression. It can be hard to tell the difference between memory loss and confusion due to depression. Some types of memory loss may cause you to forget recent or new events, past or remote events, or both. You may forget memories from a single event, or all events.
Memory loss may cause you to have trouble learning new information or forming new memories.
The memory loss may be temporary (transient), or permanent.