New findings on epileptic memory disorders

Let's say you go to visit an acquaintance
you haven't seen in a long time.
Still, you'll not hesitate to press the right doorbell: apple trees in the front yard and wooden birdcages next to it, fences painted bright red, clinker facades - all this indicates that you have come to the right place
.

Each place has many different characteristics that make it unmistakable as a whole
.
Therefore, in order to remember a place, we need to store a combination of these characteristics (this also includes sounds or smells).

Because only in this way, when we visit it again, we can confidently recognize it and distinguish it from similar places
.


In patients with chronic epilepsy, the preservation of this precise combination of features may be impaired
.
At least the current findings point in that direction
.
Dr.
Nicola Masala, a neuroscientist at the Institute of Experimental Epilepsy and Cognitive Sciences at Bonn University Hospital, explains: "In this study, we looked at neurons
in the murine hippocampus.
"

When a place is visited, specific neurons are activated

The hippocampus is an area
of the brain that plays a central role in the memory process.
This is especially true for spatial memory: "There are so-called location cells in the hippocampus," Massala said
.
These help us remember the places
we've been.
"There are about a million different location cells
in the hippocampus of mice.
Each reacts
to a combination of specific environmental characteristics.
So, to put it simply, "apple tree/birdcage/fence" also has a local cell
.

But how do you ensure that the positioning unit only responds to a combination of these three features? This is ensured by a mechanism called "tree integration"
.
Because the position cells have a long extension, dendrites
.
These places are littered with a large number of touchpoints where we can receive information about a place that our senses transmit to us (in fact, there are often hundreds or thousands of touchpoints).

These contacts are called synapses
.
When the signal reaches many adjacent synapses at the same time, a strong voltage pulse may form in the dendrites—so-called dendritic spikes
.

In this way, dendrites integrate different types of location information
.
Peaks
are only possible when they are all clustered together.
Only then will the combination be stored so that we will recognize it the next time we visit the house of an acquaintance
.

"However, in mice with epilepsy, this process is impaired," explains Professor Heinz Beck, Dr.
Masala, who completed his PhD in his
research group.
"When only a few synapses are stimulated, spikes already appear
.
Stimulation also does not need to occur
at the same time.
One might say: sick rodent cells don't look
so closely.
They opened fire
on all houses with apple trees in their front yards.
Therefore, the stored information is less specific
.
We were able to demonstrate experimentally that affected animals have greater problems in distinguishing between familiar and unfamiliar places"
.

Active substance improves memory

But the reason? In order to form spikes, a large number of charged particles (ions) must flow into the battery
.
To achieve this, stomata – ion channels
– are opened on the membrane surrounding the dendrites.
"In our experimental animals, special channels for sodium ions are significantly more prevalent in dendritic membranes than normal," explains Dr.
Tony Kelly of the Institute of Experimental Epilepsy and Cognitive Science, who co-supervised
the study.
"This means that a few less synchronized stimuli on the synapse is enough to open many channels and trigger spikes
.
"

There is an inhibitor that very specifically blocks the affected channel, preventing the inflow
of sodium ions.
"We injected the animals with this substance," Massala said
.
"This normalizes
the discharge behavior of their dendrites.
" They are also better able to remember where
they have been.
”

Thus, this study provides insight into
the memory retrieval process.
In addition, in the medium term, it is expected to produce new drugs
for improving the memory of epilepsy patients.
These promising results are also the result of fruitful cooperation, Masala emphasizes: "This success would not have been possible
without the collaboration with the laboratories of Prof.
Dr.
Sandra Blaess, Prof.
Laura Ewell and Prof.
Christian Henneberger at the University of Bonn.
"