The brains of people with epilepsy are not the same
as the brains of the general population.
A new study by Stanford University
epilepsy specialists(1) found electrical activity in epilepsy
patients’ brains which can explain brief lapses in thinking, perceiving and remembering
even in those whose epilepsy seems to be well-controlled by medication.
High-frequency oscillations (HFO) are subtle,
transient brain recording signals that erupt up to 100 times per minute in
people who do not have epilepsy. However, these HFO “buzzes” are abnormal if
they occur with an onset of a seizure in
epileptogenic areas of the epilepsy patient’s brain. The HFO buzzes are
not abnormal if they occur in parts of the epilepsy patient’s brain that are not
associated with their seizures.
In their study, the Stanford researchers tested six
patients with intractable seizures who had sensors implanted in their brains
for consideration for possible epilepsy surgery. Cognitive challenges were
presented to the patients for them to solve during periods when a buzz of
epileptic activity was interfering with their brains’ normal processes. Several
HFOs per minute were seen on EEGs but clinical seizures were undetectable to observing
neurologists. The researchers suggest that these HFOs could explain cognitive
complaints from otherwise “normal-appearing,” epilepsy patients whose epilepsy
is “controlled.” If the HFO occurred milliseconds before a seizure-prone brain area
began processing information the HFO seemed to affect cognition The HFOs lowered
the accuracy and speed of the patient’s thinking, i.e., the response time, even
though visible seizure activity was not observed.
The explanation for this brief deterioration is that
HFOs within that period interfere with high-frequency broadband events, or HFBs.
These healthy brain events occur in brain areas that are not affected by the
epilepsy focus. HFBs are associated with a brain circuit beginning to do
something the brain is supposed to do, as processing visual information or
recalling previous experiences. HFOs can disrupt healthy brain activity for up
to one second even though clinical seizure activity is not apparent.
A computer was trained to accurately distinguish
between HFOs and HFBs. In all six patients studied, if a spontaneous HFO
occurred within one second before a task-elicited HFB should have arisen, it
disrupted, delayed, diminished and often completely extinguished the HFB.
Testing at these times showed this event slowed responses, showed poorer recall
and reduced confidence in answering memory-evoking questions.
The important conclusion from this study is that the
epileptic tissue’s performance was normal outside the window of the HFOs. For
the majority of the time when seizure-prone brain tissue isn’t experiencing HFOs,
the brain tissue worked well in these test patients. Researchers advised that prior
to surgery for its removal, physicians should weigh that much of the time the
epileptic focus that is seizure-controlled can still have significant cognitive
abilities. Is surgery to remove it still the best treatment considering
side-effects?
Bruce Goldman, a science writer in the Office of
Communications at Stanford University, reviewed the researchers’ scientific
article.
1)
Liu S, Parvizi J.
Cognitive
Refractory State Caused By Spontaneous Epileptic High-Frequency Oscillations In
The Human Brain. Science Translational Medicine Vol. 11,
Issue 514, 16 Oct 2019.
Lance
Fogan, M.D. is Clinical Professor of Neurology at the David Geffen School of Medicine at UCLA. “DINGS”
is his
first novel. It is a mother’s dramatic story that teaches epilepsy, now available in eBook,
audiobook and soft cover editions.
