Track Symptoms of Alzheimer's Disease

What's Happening in the Brain

Memory is what gives meaning to our lives. Memory is at the basis of how we interpret our world - in the first instance, whether what we sense around us is familiar to us. In the brain memory structures are linked to structures that tell us whether we need to be afraid, whether we need to fight off the new threatening things sensed in our environment, or whether we need to run away. Memory structures also let us know that the environment is familiar and reassuring.

'Memory' is the brain's storage and retrieval information. Because memory is so basic to survival, and so much influences brain function, there are many ways to think about it. One way is to think of two different forms, a 'short term' store and a 'long term' store. The brain structures that play an important role in memory are called the hippocampus , the frontal lobes and the diencephalon .

Long Term Store: The long term store is the memory of past events and experiences. It is can be further broken down into two components: the memory of how to do things (procedural memory ) and language-based memory (also called 'declarative' memory, and further subdivided into semantic and episodic memory ).

Procedural memory is a person's ability to remember how to do certain skills such as riding a bicycle or playing a piano. People usually can describe procedural memory in words, but we know that procedural memory is better demonstrated than described.

Declarative memory can be expressed verbally, and includes semantic memory and episodic memory. Semantic memory is memory about the world around us. It includes things such as the knowledge that the sky is blue or the name of your mother. Episodic memory is memory for personal events such as a birthday or your wedding.

Short Term Store: The short term store is memory related to events that are presently occurring. For example, think about when you read a sentence. In order to understand what you have read, you will need to remember the first part of the sentence until you have finished the sentence.

Your brain is constantly using its short term store to remember experiences and information. Often the information will move from your short term store to your long term store. Then when the information is needed again, it can be retrieved from your long term store. For example, when you meet someone for the first time, memories of their name and what they look like are moved from your short term store to your long term store. This way when you meet them again, the information about them can be pulled from the long term store back to your short term store.

The major brain chemical that is responsible for forming memories is called acetylcholine. Drugs that are used to treat Alzheimer's disease increase the amount of acetylcholine that is available for the brain to use. They work something like this. The brain is made up of billions of nerve cells called neurons. Neurons communicate with each other by making links across the miniscule gaps between them. These gaps are called synapses. Communication across the gap occurs by the release of brain chemicals from the transmitting neuron to the receiving neuron. These brain chemicals are called neurotransmitters.

There are many different types of neurotransmitters within neurons. The first neurotransmitter to be discovered was acetyl choline . Neurons containing acetyl choline are known as cholinergic neurons. Acetyl choline is involved in sending many types of messages throughout the brain, including those involving memory and learning. Acetyl choline is made up of two parts, acetyl-CoA and choline, which both may be found in our diet. Acetyl-CoA comes from the regular fats and sugars in our diet. Choline forms from lecithin , which is found in animal and plant-based foods like eggs, liver, peanuts or soybeans. Acetyl-CoA and choline are joined together in the neuron by a type of protein called an enzyme , forming acetylcholine. This neurotransmitter travels to the end of the neuron where it is released into the synapse. Acetyl choline carries a chemical message which is recognized by special sites on the next neuron. The message is sent until another enzyme enters the synapse to break down acetyl choline. This enzyme is called acetylcholinesterase . At this point the message stops until the process begins again.

In Alzheimer's disease, the amount of acetyl choline is diminished. The original strategy to replace acetyl choline was simply to add items like lecithin to the diet. This strategy proved to be ineffective for a number of reasons. Also unsuccessful was supplying more acetyl choline, or drugs that functioned like acetyl choline. Finally, the best approach was to inhibit the brain enzyme that breaks down acetyl choline. This causes the levels of acetylcholine in the synapse to increase. The enzyme that breaks down acetyl choline is called acetylcholinesterase, and thus the drugs that inhibit it are called cholinesterase inhibitors .