When we were children, our brains operated like well-oiled machines. We could soak up new information and remember what we learned — at least long enough to get us through our next social studies test. We took our brains for granted.

But we got a little older — then a lot older — and now we forget where we left our cellphone, the name of the new co-worker we met at the office party, the name of the movie we just saw. For some people, “dementia” and “Alzheimer’s disease” are no longer vague concepts, but imminent nightmares.

In this two-part series, we’re going to explore how our brains learn and retain information, what happens as we age, what’s normal and what’s not and what we can do to keep our brains humming at high gear.

Meet Your Brain
The human brain weighs about three pounds. In that relatively small structure is everything that makes us who we are — our thoughts, feelings, biases, memories and knowledge. It’s where both our conscious and our subconscious behaviors reside. When you try to hit a tennis ball, your conscious brain is guiding your strategy, but behind the scenes your subconscious brain is altering your breath, your footwork and your swing.

The brain consists primarily of two types of cells. Neurons, or nerve cells, are the key cells involved in learning and memory. They transmit signals throughout the brain both electrically and chemically. Glial cells insulate these neurons and provide them with structural and metabolic support.

Each neuron is separated from its fellow neurons by a small space called a synapse. Neurons talk to each other when one neuron releases a chemical called a neurotransmitter that crosses that synapse and activates the adjacent neuron. Each neuron forms many synapses with many different neurons: The human brain contains about 100 billion neurons and approximately 100 trillion synapses.

How We Learn and Remember
The synapse, that small space between the neurons, is where the most important action takes place when we learn something new. To form short-term memories, the neurons release greater quantities of neurotransmitters across the synapse, making that pathway stronger and more efficient. To form long-term memories the brain must create more synaptic connections along the active pathway. Converting short-term memories into long-term memories is something we’re very good at when we’re young, but that transition starts to get muddled as we get older, making it harder to learn and remember.

Normal Brain Aging
As early as the end of our teenage years, our ability to come up with novel, creative solutions to new problems already starts to wane. Once we hit our 40s, virtually all of us will have what is called “benign forgetfulness” — you can’t remember where you put your keys, you forget appointments, names or where you parked your car. By age 70, the majority of us will have significant memory issues.

Our short-term memory formation remains largely intact, but our ability to convert those experiences into long-term memories begins to suffer. Brain studies reveal that this normal aging process is associated with a decrease in the number and activity of synapses in the memory-forming regions of the brain.

Am I Normal?
If you’re asking this question, the likelihood is that the answer is yes. It’s a very loose guide, but if you are concerned about your memory, chances are you are fine. If others — for example, family and friends — are worried about your memory, then there may be a more serious problem.