As part of reporting on neurosurgeon Robert Gross’s work with patients who have drug-resistant epilepsy, I interviewed a remarkable woman, Barbara Olds. She had laser ablation surgery for temporal lobe epilepsy in 2012, which drastically reduced her seizures and relieved her epilepsy-associated depression.
Emory Medicine’s editor decided to focus on deep brain stimulation, rather than ablative surgery, so Ms. Olds’ experiences were not part of the magazine feature. Still, talking with her highlighted some interesting questions for me.
Emory neuropsychologist Dan Drane, who probes the effects of epilepsy surgery on memory and language abilities, had identified Olds as a good example of how the more precise stereotactic laser ablation procedure pioneered by Gross can preserve those cognitive functions, in contrast to an open resection.
Olds told me she had held a variety of jobs in her life, ranging from manager of a supermarket to her favorite, ballroom dance instructor. She had been diagnosed with epilepsy at age 5, but the seizures were well controlled with medication until later in her life. She had tried several anti-seizure medications but they were not effective. Several years ago, Olds had a vagus nerve stimulation device implanted, which had some calming effect; she described how she would swipe a magnet over the device when she started to have pre-seizure feelings. Even so, her seizures had prevented her from driving, and the successful surgery considerably improved her mobility.
In many epilepsy patients, the seizures primarily arise on one side of the brain; in Olds’ case, the right side. Usually, that side displays low activity and signs of atrophy when examined by brain imaging, indicating that during the patient’s life, important functions have been concentrated on the healthy, non-seizure-triggering side. But I continue to be surprised to find how using a laser on a region of the brain (the hippocampus) that scientists think is critical for learning and memory can have such a small effect.
Drane’s 2014 paper on the cognitive effects of the stereotactic procedure says that some patients underwent hippocampal ablations on their dominant side.
Significant decline occurred with the open resection patients across all range of performance, while patients undergoing SLAH tended to remain stable or showed slight improvement. The SLAH sample included several individuals who were employed in high-level professions (e.g., physician, school teacher) who underwent dominant hippocampal ablations. These patients were considered to be at a high risk of decline with standard ATL surgery based on their baseline level of function. Finally, significant changes in performance, even in the patients at the low end of the spectrum of functioning, have measurable life impact. For example, one mildly intellectually disabled individual who experienced significant gains on naming measures was described as “better able to communicate†by his family, and began to participate in a full-time sheltered workshop for the first time in his life.
Drane himself has argued that his research points to a less critical role for the hippocampus in memory and language functions than that suggested by the story of HM, whose resection extended way beyond the hippocampus anyway.
I have asked neuroscientists who experiment with animals about this issue. One cited the brain’s remarkable plasticity, and said that epilepsy would tend to gradually push important cognitive functions to the healthy side. Another used a metaphor, describing a painter who has his hands cut off, who must learn to paint with his mouth or feet. This scientist said that deficits induced by lesions in regions of the brain important for memory formation can be overcome by extensive training that recruits other parts of the brain.
Does this explain the surprisingly small effects of the stereotactic ablation procedures? I think it could be a topic for a writer well versed in neuroscience to expand on.
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