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Dr. Mike Evans

Welcome to Health Advisor, where contributors share their knowledge in fields ranging from fitness to psychology, pediatrics to aging. Follow us @Globe_Health.

This is the first instalment of a series that will explore the question: Am I Normal?

It's hard not to be fascinated by the abnormal in medicine, however, when we consider our own health, the most common question I get in the clinic is "Are these symptoms normal?"

Often these question relate to memory: Are the multiple memory lapses you have in your daily journey normal? What if the frequency of these "moments" is escalating? Does that mean dementia or Alzheimer's? What's normal for memory as we age?

A wild guess would be that in in the last month you have misplaced your keys, forgotten someone's name, lost a thought midway through a discussion, or found yourself pressing buttons on your key fob in a parking lot hoping for bright lights.

The short answer is that this is normal, but to understand the variance, it is very helpful to know a bit more about deposits and withdrawals from the memory bank.

Most people think of memory as short term or long term. That it is one system that remembers what you had for dinner last night and what you wore at your prom night 40 years ago. Memory researchers now see a much more complex interconnected system that can be oversimplified into four key types of memories: episodic (personal experiences), semantic (knowledge), procedural (physical memory such as playing an instrument or hitting a golf ball), and finally, working memory.

There are some fascinating memory subplots, such as our tendency towards distortion of our autobiographical episodic memory, or the fact that we can actually forget how to ride a bike, but the answer to our question regarding variance lies mostly with the working memory. You see, our working memory is our front-end processor and problem solver. If I ask you to give me the right change, tell you directions to my house, or give you my phone number, it's your working memory that's on it. It's going all the time (if not, you are in a coma) and makes meaning of our days. Your working memory is also limited and can only juggle, the scientists say, about four things at a time (unless you are my daughter and then it's 18).

On that note, working memory is the memory system most affected by normal aging. If we ask a 17 and a 71 year old to recall words, the teenager will usually do better, but the 71 year old is crafty and often "associates" the word to keep up. For example, you might remember that a plane has two wings to remind yourself of your 2 p.m. flight. Brain positron emission tomography (PET) scans show this adaptation as different parts of the brain light up when seniors remember things as compared to youngsters.

It's one thing to learn how working memory is affected by aging, or mental health diseases like depression and anxiety. But what helps my patients most is understanding that it is normal to have your working memory compromised by garden-variety issues such as stress and worry. A memory has to be filed to be pulled. When we are stressed or anxious, or even just too busy, this leads to inattention and the memory doesn't get filed.

It is also very normal to be scared of losing your memory. Your memory bank is you. It's also a rational fear, as we may be the first generation where many of our bodies will outlive our brains, rather than vice versa.

Misplacing keys is normal; forgetting what they are for is dementia. Forgetting a person's name is normal; not remembering knowing the person is not. Forgetting to turn into a familiar street is normal; becoming easily disoriented or lost in familiar places for hours is not. These lines are distinct for most of us, but in early dementia patients, it can be tricky to tell.

Dr. Mike Evans is a staff physician at St. Michael's Hospital, an Associate Professor of Family Medicine and Public Health at the University of Toronto, and a scientist at the Li Ka Shing Knowledge Institute. Dr. Evans curates resources and information for a range of common conditions on his website, and runs a different kind of health lab that fuses filmmakers and illustrators with clinicians and best evidence. His video, 23 and ½ hours, has been seen by over 4 million people and his Medical School for the Public on YouTube has been viewed by over 8 million. Follow him on Twitter @docmikeevans