There have been many studies to show CBD has a profound role in antagonising (opposing) the negative effects of THC, most notably acting as a neuroprotectant preventing and even reversing any memory damage from constant THC exposure
This isn't the only instance where CBD acts as a neuroprotectant. Alzheimers disease (AD) is characterised by dementia (memory loss) and loss of motor skill functions, common in old age.
Multiple studies have shown huge improvements of symptoms of AD including slowing down the onset of dementia.
A study shows that CBD is effective for treating Alzheimers Disease (AD), a neurodegenerative disease characterised by dementia (memory loss) and a loss of motor skill functions.  THC actually worsens the AD increasing the speed of onset and severity. However, CBD significant reverses process preserving brain function: memory and motor skill functions. There is evidence to show THC and CBD together can improve symptoms of AD and memory function if the correct ratios are used. 
CBD levels are very low in normal cannabis flower. There is evidence to show regular exposure to THC without the presence of CBD over long periods of time can damage your brain, particuraly your memory. With cutting edge new cannabis science, cannabis has been grown to yield high concentrations of CBD with low concentrations of THC called CBD Flower.
In conclusion people who regularly consume THC or are experience age related memory problems should supplement with CBD in order to conserve their cognitive ability with CBD Oil being the most common form of administration globally. The effects are cumulative so long term supplementation will be deemed most effective.