Hormones and Memory in Couch Potatoes and Fit People

This post was originally published on January 2nd, 2014, as part of Dr. Schon’s “Exercise and the Brain” blog on wordpress.com.

In a recent study, we have found that people with lower amounts of a hormone known as Brain-Derived Neurotrophic Factor (BDNF) in their blood performed better on a recognition memory task. Interestingly, this was true for sedentary young adults, but in high-fit individuals, the reverse was true: people with higher amounts of BDNF in their blood did better on the memory task. Our study provides additional support for a link between exercise/fitness and learning and memory through hormones known to be increased following exercise.

Your snapshot or your friend’s photo?

In our study, healthy young adults, most of whom were college students, viewed pictures of outdoor scenes. Imagine taking snapshots with your friend’s camera while on vacation in the snowy White Mountains of New Hampshire. You take dozens of digital photographs. Now imagine having to sort through hundreds of photographs, some of which you took, but some of which are unfamiliar. Your friend recently took photos on a different vacation in the Swiss Alps and forgot to delete them before lending you her camera. Oddly, when you download the digital pictures hers and your photographs are now completely jumbled up.

As in this scenario, we had our participants sort through over 200 photographs, some of which they had seen just 15 minutes earlier, some of which were unfamiliar. The study participants indicated with a button press if a scene was old (they remembered taking the photo) or new (the photo is unfamiliar; their friend must have taken it). We then determined accuracy on the memory task by simply subtracting the number of new pictures they thought they had seen before (“false positives”) from the number of old pictures they correctly identified as old.

How was aerobic fitness assessed and hormone levels determined?

Our participants performed a treadmill test. During the test, we gradually increased both the speed and incline of the treadmill, making the test harder and harder over time. At the same time, we measured the amount of oxygen and carbon dioxide in their breath using specialized equipment. The photo, above, shows the snorkel-like mouth piece that was attached to a computer via a hose through which our participants had to breathe during the treadmill test. The maximum amount of oxygen reached during this test was our measure of cardio-respiratory (aerobic) fitness. We determined hormone levels from small venous blood samples that we took from each participant’s arm.

Chicken or egg and why should I care?

In animal models, BDNF protein levels and expression of the BDNF gene are increased in exercising mice in a brain region known as the hippocampus. The hippocampus is a brain area important for the formation of new memories. Your hippocampus will help you remember which snapshots are yours from the recent trip to the White Mountains. Like a fertilizer for plants, BDNF enhances the growth of new brain cells and improves the communication between these cells.

Unfortunately, we don’t know cause and effect and we didn’t look at the effects of exercise on BDNF levels and memory task performance. Did fitness increase BDNF and improve memory? While there is support from animal models that this is the case, based on our data alone, we simply can’t tell. Taking BDNF out of the equation, there was no relationship between fitness and memory. Questions remain to be answered.

We will be continuing this line of research by testing if memory improves following an exercise training program in both young and geriatric adults, and by adding brain imaging techniques”

This is a statement I recently made about this research to the Office of Communications at Boston University where we performed this research. The study was published online in November 2013 in Behavioural Brain Research (abstract).