We all know that exercise is good for the body, but new lines of evidence suggest beneficial effects for the brain as well. For the first time, RNG researchers have shown that exercise begun in old age reverses memory impairment in rats, a therapeutic effect linked to massive increases in synaptic numbers throughout the hippocampus.
Our goal was to determine if a brief period of physical exercise, in the form of voluntary running, was sufficient to boost older rats’ memory and explore which brain mechanisms may be important.
The first challenge was to find a memory test that was sensitive to brain ageing in the rat, reliable over multiple tests, and not influenced by generic ageing-related changes such as worsening vision or slowness. We discovered that Rodent Recognition Memory was the ideal memory test for this purpose. In fact, Place Recognition Memory dropped by 58% in old rats compared to young, but had no effect on Object Recognition Memory. We also found that Place Recognition Memory was strongly correlated with numbers of synapses (brain connections) in the hippocampus, the well-known memory centre of the brain.
Next, was our key test of the effect of physical exercise in our older animals. At 20-months of age (roughly equivalent to a 65 year old human), rats ran voluntarily for only 12 weeks, but the effects on both memory and the brain were remarkable.
We made three key discoveries. First, voluntary running was capable of fully reversing the animals’ place recognition memory dysfunction (Figure above). Second, this type of physical exercise dramatically boosted older animals’ synaptic numbers (Figure below), in some areas to even beyond those of young animals! Third, voluntary running also increased neurogenesis (production of new baby neurons) in the hippocampus.Finally, we explored which brain change – synaptogenesis or neurogenesis – was tied to running’s therapeutic impact on place recognition memory. Results were clear. Increased synaptic numbers was closely linked to memory improvement whilst neurogenesis was not.
This research therefore reveals new insights into the therapeutic mechanisms of physical exercise on the older brain. It also helps explain recent human studies that show physical exercise can protect older individuals from cognitive decline and may help prevent dementia.
This research was published in the prestigious journal Biological Psychiatry (corrected proof, available online 16 July 2012):