The brain remembers things over the long term as well as being a tool used for thought in the moment. This process of storing things after processing them is long term memory. Long term memory is not used just for storing information about past personal experiences; it also is responsible for remembering facts such as capital cities of the world or historic speeches, but not how it acquired these pieces of information. There are two types of long term memory, declarative and procedural. Declarative or explicit memory refers to all the memories that are available in the consciousness. It is possible to break down declarative memory into two further subcategories -- episodic memory, that encompasses personal experiences, and also semantic memory, which is knowing, for example, that the capital city of Australia is Canberra. The other type of long term memory is known as procedural memory and is the type of memory that holds knowledge of body movement or the way to manipulate objects. An example of this would be how to use a computer.
People remember different types of information. The sensory organ -- the eyes, ears, tongue, nose and skin -- pick up information that is sent to the brain for processing. The brain can then remember this information in isolation but also the information in context of an event. For example, the brain can remember the smell of garlic, but also remember the smell of garlic at a particular time while it was being cooked. People also remember their thoughts and their actions, though they do not always have the ability to distinguish between them.
Long term memories are stored in a variety of units, ranging from very large memories to small fragments. For example, a memory may be of a murder story in the news, as well as small details of the story. Some people remember the gist of the information and some people have the capacity to remember more specific details.
Memory is created as a result of three processes: encoding, storage and retrieval. Encoding is the process when information enters the cognitive system. Storage is when this system is stored in the memory. Retrieval is when this information is processed later on. The system of memory creation is not as simple as this, but it is a helpful guideline for explain the process.
Several factors have an effect on the quality of memories formed and there are techniques based on these factors to improve long term memory. For instance, the longer people are exposed to a piece of information the more likely the information will lodge in the brain. Also the more times people are exposed to information the more likely they are to remember it. Memory is more likely to form if the person is actively thinking about the subject rather than passively, in what is also referred to as incidental learning.
Biologically, the creation of long term memory differs in method to that of short term memory. Long term memory is created by the building of new proteins within the body of the cell. Especially important is the construction of synapse pathways, transmitters, and receptors that strengthen the communications between neurons in the brain. New proteins are produced whose sole purpose is to reinforce the synapse after the discharge of a certain signaling substance in the cell. This release, in a hippocampal cell, relies upon a binding molecule, magnesium, being discharged after significant, repetitive signaling by the synapses. The discharge of magnesium frees NMDA (N-Methyl-D-Aspartate) receptors in the brain to release calcium in a signal leading to gene transcription and the creation of reinforcing proteins. This process is called long-term potentiation.
One of these newly created proteins in long-term potentiation is critical for the maintenance of long term memory. It is an active form of the enzyme protein kinase C or PKC for short. PKC maintains the synaptic strength needed to keep long term memories in the brain. If PKC is inhibited for whatever reason then long term memory cannot be formed. With the removal of the inhibitor for PKC, long term memory can be formed again with no lasting effects. PKC does not affect the formation of short term memories.