- Deep brain stimulation involves
implanting electrodes deep inside the brain and passing electric currents.
- Previous research had stated that deep brain stimulation (DBS) caused
a 64% improvement in memory.
- However, recent
research has proved that DBS caused memory impairment by at least 5% to
brain stimulation of the areas in the brain, which are associated with memory
, does not improve
findings are from the latest study conducted by researchers from the Columbia
University and published in Neuron
‘Direct deep brain stimulation does not improve memory, it can be used to alter a neural process as complex as memory.’
of the brain involved in memory are hippocampus and associated structures in
the medial temporal lobe, including the entorhinal, perirhinal, and parahippocampal
study opposes an earlier research conducted in 2012, that was published in
The New England Journal of Medicine
. The research had stated
that there was a 64% improvement in memory of patients subjected to deep brain
current study states that none of the participants showed any improvement. On
the other hand their memory was impaired by at least 5% to 20% with
researchers still believe DBS would be a possible
intervention for individuals with memory problems caused by disease or trauma.
The findings suggest that if this specific form of stimulation
diminishes memory performance, there may
be other approaches that may improve it.
"We may need a different kind of
stimulation protocol to affect this region in a good direction," says lead
investigator Joshua Jacobs, assistant professor of biomedical engineering at
Columbia's Fu Foundation School of Engineering and Applied Science.
Deep Brain StimulationDeep
an invasive, neurosurgical procedure. It involves implanting electrodes deep
inside the brain and passing electric currents through it to stimulate the
electrical impulses target specific parts of the brain and change the brain
activity. It helps to regulate abnormal impulses or certain cells and chemicals
in the brain.
has beneficial effects for conditions like Alzheimer's disease, Parkinson's disease, different forms of dementia, major
depression and obsessive-compulsive disorder.
The study titled "Memory Enhancement and Deep-Brain
Stimulation of the Entorhinal Area" was conducted by Nanthia
Suthana and colleagues in 2012.
had recruited seven patients suffering from epilepsy who had electrodes
implanted in their brain for mapping seizures. Epilepsy may affect the memory
completed a spatial learning task. Spatial navigation depends on spatial
memory. Median temporal lobe plays an important role when it comes to spatial
While the left medial temporal
lobe controls verbal learning, the right medial temporal lobe is
responsible for nonverbal learning.
findings from the study showed that spatial learning in humans could be improved by electrical stimulation of the entorhinal region, a specific site
within the medial temporal lobe and the chief gateway into the hippocampus.
The stimulation of the
entorhinal region while subjects were learning, improved memory performance. Recent Study
findings from the previous research were
encouraging, the evidence suggested that
the kind of stimulation used would actually inhibit
neurons and potentially impair memory.
"We had conflicting
thoughts," says Jacobs. "So we thought it would be important to
replicate this kind of finding."
Similar to the previous study,
researchers recruited epilepsy patients. But the number of participants were
A spatial memory
task that involved remembering the
location of an object in a 3D virtual space was
conducted and participants had
to navigate through the space to find an object.
During control sessions, they
received no stimulation. In stimulation sessions, they would experience 50
pulses of electrical current per second for 5 seconds.
"Stimulation occurs only
during the time that people are encoding the memory," says Jacobs.
"The task was well controlled."
A verbal memory
task that involved recalling words
on a list was also conducted.
Electrical pulses were delivered while participants studied the list, for 4.6 seconds.
Results of the Current
None of the participants showed
statistically significant improvement in memory after stimulation.
Stimulation of the
entorhinal cortex resulted in a reduced accuracy in memories of 9% compared to
Stimulation of the hippocampus
resulted in 8% impairment of memory.
across all regions that were stimulated ranged
from 5% to 20% for both tasks.
Minor differences in the two
- Number of participants - 7 in the previous study and 49 in the
- Number of memory retrieval tasks per session- 6 in the previous study and 48 in the current study.
- Difference in measurement of spatial memory - to measure the
spatial memory, in the previous study, participants revisited the 3D
virtual space while the objects remained visible in the space during the
recall test. This may have skewed the results in the positive direction.
While in the current study participants revisited the 3D virtual space, without the object being present in the space and without stimulation and navigated to the place they recalled to be the object's
calculated the difference in the
remembered locations from actual locations.
"It's quite a bit bigger and
more statistically powered, so it's more likely to produce accurate
results," says Jacobs.
"Theirs was a first study of
its kind," says Jacobs. "It's important to improve the protocol in a
way that quantifies spatial memory more precisely."
Though improving memory
is not possible through deep
brain stimulation, it maybe possible to alter a neural process that is as
complex as memory, using electrical stimulation.
"The simple approach to
stimulation doesn't work very well, so we're trying to develop a more advanced
approach," he says.
Researchers are now working to devise more complex DBS interventions that respond to
brain activity in real time and boost memory in the positive direction.
The study titled "Direct electrical stimulation of the human entorhinal region
and hippocampus impairs memory"
conducted Joshua Jacobs and colleagues.
- Benefits of Deep Brain Stimulation for Alzheimer's - (http://www.alzheimers.net/8-3-15-benefits-of-deep-brain-stimulation-for-alzheimers/)
- Nanthia Suthana. Memory Enhancement and Deep-Brain Stimulation of the Entorhinal Area. The New England Journal of Medicine; (2016) DOI:10.1056/NEJMoa1107212