Adaptive and targeted brain stimulation
The DBS devices currently available are ‘open loop’, i.e., stimulation settings are fixed by the neurologist following surgery and a period of recovery. Subsequent adjustments to stimulation levels can only be made when a patient visits the clinic. Existing devices are therefore incapable of changing in response to each patient’s changing clinical state. Therefore, at any time, stimulation may be insufficient or excessive. These shortcomings compromise the effectiveness of DBS and can lead to side-effects.
These issues can be overcome by using a ‘closed-loop’ strategy, in which stimulation is automatically adjusted according to the fluctuating severity of symptoms. This can be done by deriving indicators of symptom severity from the electrical activity of the patient’s brain (‘biomarkers’). The biomarkers can then be used to control the stimulation applied.
In 2015, we commenced a major clinical study with people who are living with movement disorders (particularly Parkinson’s disease) and receiving an existing commercial DBS device. The aim of this study is to identify relationships between symptom severity and biomarkers derived from brain electrical activity, and to determine the best stimulation parameters for alleviating symptoms with minimal side effects. The identified relationships and optimum stimulation parameters will then be used to apply and evaluate closed-loop DBS.
Inadequate clinical outcomes with DBS and the emergence of undesirable side-effects are highly dependent on accurate electrode location which varies even with the best surgical technique. After implantation there is limited scope to focus stimulation onto the ideal target in the brain. Our aim is to develop “current focusing” stimulation strategies for our device. With these techniques, the pattern of electrical stimulation will be tightly focused to target specific regions of the brain, thus minimising any adverse side-effects. These studies will be informed by the results of ongoing and complementary studies in cochlear implants and the bionic eye.