Deep brain operation

Regaining the self

Electrical stimulation offers hope for the victims of serious head injuries.

These words from a children's poem by Theodor Seuss Geisel, better known as Dr Seuss, capture the basic essence of what it is to be human: to have consciousness. Yet millions of people lose this basic ability through brain injury. In some severe cases, patients are left in a minimally conscious state, with little or no capability of making conscious decisions.

The neural networks in these patients are capable only of limited function because their connections are impaired. This causes restricted communication and incomplete awareness of surroundings. 

Patients in such a condition are often neglected and underrepresented. Until recently, no treatment has been known to help those people who had been in a minimally conscious state for longer than a year. Now, however, there is a growing feeling among neurologists that Deep Brain Stimulation (DBS) may have the ability to retrieve limited consciousness.

Wake-up call

In 2005, one pioneering DBS case study by a team of neurologists, psychologists, neurosurgeons, and bioethical consultants from the US was performed on a 38-year-old New Jersey man who was left in a minimally conscious state having survived a violent assault in 1999.

After the assault, this patient lay in a hospital bed, silenced due to his brain injury, with his eyes closed, little motor ability and feeding tubes in his stomach.

In the case study - authored by Dr Nicholas Schiff, of Weil Cornell Medical College and the Director of the Laboratory of Cognitive Neuromodulation in Ithaca, New York, with neurosurgery performed by Dr Ali Rezai of the Cleveland Clinic Foundation in Ohio - the team first conducted tests to determine that this patient's critical communication networks were present.

"Multiple factors are used for patient selection, including the mechanisms of injury, clinical status, coma-recovery standardised scale assessments, neurological, neurosurgical, physical therapy, speech assessments, high-resolution structural imaging, functional Magnetic Resonance Imaging (MRI) and Positron emission tomography (PET) scans," says Dr Rezai.

The team was able to see that the patient's critical communication region, which is essential for consciousness, was not sending and receiving signals properly. The team thought that the region was still intact and could be resituated, even though most of the cortex - the area in the front of the brain that controls consciousness, emotion, language, and memory - was injured.

The crucial difference between this patient's injury and more severe ones was that the former's critical neuron connections were only damaged, but not permanently deactivated. The team hypothesised that, because his critical networks had been preserved, DBS may benefit him.

In more serious conditions, DBS would not restore neural function. Such conditions include coma, in which the patient is unconscious and cannot be aroused with stimulation, and even vegetative state, in which the victim has no awareness of self and environment but may be stimulated.

The critical level of neural preservation is in the region called the thalamus. This area routes sensory impulses to the cerebral areas. Thalamo-cortico-thalamic circuits are believed to be involved with consciousness, sensory activity, physical functions, and, most importantly, in the understanding of the self and surroundings.

The team's goal was to use DBS in this patient to 'switch on' the areas in the frontal cortical systems.

After the surgery, the team waited 50 days to reactivate the electrodes and test stimuli to allow for any unknown variables that may have influenced the patient's motor and verbal responses.

They then performed a six-month double-blind alternating crossover test in which neither those assessing the patient, nor the family or even the patient himself knew if the DBS stimulator was turned on or off, according to Dr Rezai. The electrodes were switched on and off in alternating months in an effort to eliminate other variables and see whether the stimulation was directly related to improvement.

Initial findings

The results were remarkable. In periods of no stimulation, the patient's responses were weaker, but still stronger than the time prior to his DBS electrode implantation. There was a statistically significant relationship between stimulation and improved communication, motor, and behavioural responses.

The patient was able to hold cups, name objects, swallow foods, and express his likes and dislikes. Because he was immobile for so long, however, his movement was limited.

In this study, consciousness was shown to be restorable in a person with large-scale network damage lasting well over one year - previously thought to be the period over which irreparable damage was caused. The team demonstrated that it was possible for this minimally conscious patient to regain limited neural function and therefore limited consciousness.

In 1997, the US Food and Drug Administration (FDA) approved a similar study for 11 other patients - the first successful survey of its kind. "A single instance can be intriguing and very valuable, but the next responsible step is showing that it is reproducible," says Dr David Roberts, chairman
of neurosurgery at the Dartmouth-Hitchcock Medical Center in Lebanon, New Hampshire. 

"You need to be very careful about making probabilistic inferences conclusively," agrees Dr Kenneth Goodman, a philosopher who directs the University of Miami's bioethics course.

"In terms of neural implants, you are dealing with the human brain, which is as complicated as anything that gets in this galactic supercluster."

Unanswered questions

Dealing with something as challenging as reawakening the mind raises ethical and procedural questions of similarly cosmic proportions. "How can we best perform an experiment that safely gathers data from people into whose brains we've put an electrode, especially those whose brain health is already compromised?" asks Dr Goodman.

Furthermore, how would the patient deal with regaining the self after losing it for a long period of time? And how could a newly-conscious person integrate back into community?

Such a treatment would also need to be controlled and standardised. Consent from patients, or relatives, if the patient is not fully conscious, and from Institutional Review Boards is being sought before these surgeries. According to Dr Goodman, during treatment there would need to be a stable control group, so that determining results from something as complex as brain injury would be possible.

More information about this technique must be provided to the neuropsychological, ethical, public, and medical community.

So what does such a complex procedure entail? In the 1940s, before DBS, thaladotomies and pallidotomies were performed on the thalamus and globus pallidus parts of the brain. In these surgeries, functional disorders destroying or disrupting signals in the brain by making permanent, non-reversible lesions, were treated.

In the 1990s, a shift away from such risky, non-adjustable, non-reversible methods towards DBS began to sweep Europe and then the US. This was a major step towards the treatment of neurological dysfunction.

"Instead of destroying tissue that is augmenting function, you have a procedure stimulating the brain to achieve the same effect," explains Dr Roberts. "In DBS, stimulation can be increased, decreased, or turned off."

Engineering challenge

"The part of the DBS procedure that could be made more efficient is programming automation of the stimulator. That is the next challenge for engineers working together with neurosurgeons," says Dr Gordon Baltuch, Director of the Center for Functional and Restorative Neurosurgery in Philadelphia, Pennsylvania.

Still, more research in this area is essential. "The intersection of biomedical engineering and ethics is an exciting new frontier," in the words of Dr Baltuch.

The case study of the 38-year-old assault victim showed that treatment for long-term minimally conscious patients is possible and provides hope for other electrode-stimulation techniques.

DBS has shown promising results in the alleviation of movement disorders such as Parkinson's disease, essential tremor and dystonia as well as pain syndromes, epilepsy, some psychiatric conditions and even obesity. In traumatic brain injuries some consciousness can potentially be restored with this revolutionary technique too.  

DBS testing in Canada, Japan, and the US has found that obsessive-compulsive disorder and treatment-resistant forms of depression - the leading cause of disability in North American adults under 50 (according to the World Health Organization) - are already being improved with DBS therapy.

Furthermore, the FDA has approved DBS treatment for certain movement disorders. Thousands of Parkinson's disease sufferers have been treated with it since its approval in 1997, whereas DBS treatment of some forms of dystonia was vetted by the FDA in 2003.

DBS challenges conventional ideas about neurological dysfunction and the restoration of consciousness. Indeed, thanks to this treatment, patients may be given back the power to "steer themselves in any direction", as it was put by Dr Seuss.

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