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.