Rare reversible cerebral atrophy

European moles face an existential crisis
in harsh winters.
Their mammalian metabolism requires more food
than in the coldest months.
Instead of coping with seasonal challenges by migrating or hibernation, the moles came up with an unexpected energy-saving strategy: shrinking their brains
.

In a recent study, a team at the Max Planck Institute for Animal Behavior, led by Dina Dechmann, found that the brains of European moles contract 11 percent by winter and back 4 percent
by summer.
They are a new mammal known for
reversibly contracting the brain through a process known as the Denier phenomenon.

The European mole rat is the newest known mammal, and its brain contracts
reversibly until winter.

However, the study isn't just adding a bizarre species to animals with shrunken brains; It delves into the evolutionary mystery
of what drove them down this dangerous path.
When the researchers compared moles from different regions, they found that Denard's phenomenon was caused by a cold environment, not just a lack of food
.
Reducing brain tissue helps animals use less energy, thus fending off the cold
.

This phenomenon was first described in the skulls of shrews, which are smaller in winter and larger
in summer.
Dechmann and colleagues reported the first evidence in 2018 that these atypical changes in the shrew skull occur throughout a person's life
.
Dechmann and his colleagues have shown that the Dehnel phenomenon occurs in
stoats and weasels.
What these mammals have in common is that their lifestyle keeps them on the edge of vitality
.
The skull of the European mole shrinks before winter and regrows in the spring, a process known as the Denel phenomenon
.

Dechmann said: "They have an extremely high metabolism and are active
all year round in cold climates.
Their tiny bodies are like turbocharged Porsche engines that can drain energy
in hours.
”

For scientists, it's clear that shrinking energy-consuming tissues, such as the brain, allows animals to reduce their energy needs
.
"We know that the phenomenon of De Neer has helped these animals survive tough times
.
But we still don't know what the real pressure points driving this process are, and what the exact environmental triggers are
.
”

Now, the team is answering this question
by studying a new mammal with extreme metabolism.
By measuring skulls from the museum's collection, the researchers recorded the changes of two species of
mole—the European mole and the Spanish mole—over season.
They found that the skull of the European mole shrank 11 percent in November and regenerated 4 percent in the spring, but the Spanish mole's skull remained unchanged throughout the year
.

Because different species live in vastly different climates, researchers can determine that weather, rather than food availability, is responsible for the brain changes
.
"If it's just a matter of food, then we should see European moles shrink in winter when food shortages occur, and Spanish moles shrink
when summer heat leads to food shortages," Dechmann said.

The findings not only answer evolutionary questions, but also provide insights
into how our bodies regenerate after suffering severe damage.
Dechmann said: "These three distantly related mammals can contract and regenerate bone and brain tissue, which has great implications
for the study of diseases such as Alzheimer's disease and osteoporosis.
The more mammals we discover through Denard, the more their biological insights are relevant to other mammals, and possibly even to us humans
.
”

References:

Winter conditions, not resource availability alone, may drive reversible seasonal skull size changes in moles