The Scientist - USA (2020-05)

05.2020 | THE SCIENTIST 41

Parylak compares this situation to going to the same res-
taurant after it has changed ownership. In her neighborhood
in San Diego, there’s one location where she’s dined a few
times when the restaurant was serving different cuisine. It’s
the same location, and the building retains many of the same
features, “so the experiences would be easy to mix up,” she
says, but she can tell them apart, possibly because of neuro-
genesis’s role in pattern separation. This might even hold true
for going to the same restaurant on different occasions, even
if it served the same food.
That’s still speculative at this point. Researchers haven’t been
able to watch neurogenesis in action in a living human brain,
and it’s not at all clear if the same thing is going on there as in
the mouse brains they have observed. While many scientists
now agree that neurogenesis does occur in adult human brains,

there is little consensus about what it actually does. In addition

to the work supporting a role for new neurons in pattern separa-

tion, researchers have accumulated evidence that it may be more

important for forgetting than it is for remembering.

The importance of forgetting

It seems counterintuitive for neurogenesis to play a role in

both remembering and forgetting, but work by Paul Frankland

of the Hospital for Sick Children Research Institute in Toronto

suggests it is possible. In 2014, his team showed that when

mice made more new neurons than normal, they were more

forgetful.^10 He and his colleagues had mice run on wheels

to boost levels of neurogenesis, then trained the animals on

a learning task. As expected, they did better than control

mice who hadn’t exercised. (See “How Exercise Reprograms

1.Neuron, 91:1356–73, 2016; 2. J Neurosci, 38: 3190–98, 2018; 3.Hippocampus, 29:848–61, 2019; 4.Behav Brain Res, 376:112152, 2019.

EFFECT EVIDENCE RELATED HEALTH CONDITIONS

Most of the research into neurogenesis involves boosting

or inhibiting animals’ generation of new neurons, then

training animals on a complex memory task such as find-

ing a treat in a maze, and later retesting the animals.

Decreasing neurogenesis tends to hamper the animals’

ability to remember.^1

Alzheimer’s disease, Parkinson’s disease

Training mice or rats on a memory task before manipulating

neurogenesis has also been found to affect the strength

of the trained memory. Boosting neurogenesis reduced

the memory’s strength, perhaps an extreme form of forgetting

that at normal levels avoids the remembering of un-

necessary details.^2

Alzheimer’s disease and other forms

of dementia

Research has linked decreased neurogenesis with more

anxious and depressive behaviors in mice. Stress can

reduce neurogenesis, ultimately leading mice to be more

anxious in future stressful situations.^3

PTSD, anxiety, depression

Research has linked decreased neurogenesis with trouble

switching focus.^4

Autism

Forgetting

Emotion

Attention

Memory