This deep brain stimulation (DBS) article was written for people with Parkinson's (PwP) by an individual with Parkinson's disease. It seeks to introduce DBS and the challenge of configuring DBS settings (i.e., DBS programming). The author's knowledge is limited to personal experience of having a DBS device. This article neither addresses DBS surgery nor the matter of candidate suitability and is not a substitute for medical advice.
Deep brain stimulation
A DBS device consists of an electrical pulse generator and wires. One end of the wires connects to the generator, which is implanted under the skin (Figure 1) the other end is inserted deep into the brain. The generator can be controlled by external devices, such as DBS-programming software on a neurologist's laptop.
Figure 1: Pulse generator implanted below skin on torso. Author supplied.
The pulse generator sends pulses of electricity along the wires and into the brain (Figure 2). The generator sends around a hundred pulses per second, with each pulse delivering a small electrical current which lasts a fraction of a second.
Figure 2: Arrow indicates the end of one wire deep within the brain. Author supplied.
The wires inside the brain typically end with multiple metal electrode contacts; these are the small areas near the end of the wire that transfer the electrical pulse to the brain. Multiple contacts enable control over the direction of the electrical pulses delivered into the brain. Some pulse generators allow each electrical contact to be powered independently; these generators can send pulses with different settings to individual contacts.
The strength of a pulse is specified by the current or voltage (milliamperes or volts), its duration is the pulse-width (microseconds), and the number of pulses per second is the frequency (Hertz).
For each therapeutic pulse delivered by a DBS device, the device also delivers a pulse with the opposite electrical charge. The second pulse is often a weaker, longer lasting pulse, to maintain chemical balance around the contacts without influencing symptoms. This balancing pulse is automatically determined by the system.
Figure 3: Graph highlighting the key elements of a DBS pulse. Author supplied.
Electrical pulses? Current? Confused?
Picture a disco, with multiple lights above the dance floor. Imagine each light is equivalent to an electrical contact of the DBS device. You could switch a light on and set its brightness (equivalent to setting the strength of the current), decide how long until you switch the light off (equivalent to pulse-width), and decide how long to wait until you switch a light back on again (that is, how frequently you will switch the light on, off and on again). With a dimmer switch per light, you could switch different lights on and off, with different levels of brightness, leaving them on for different lengths of time, and choosing how rapidly to switch each light on, off and on again. Only some lighting combinations would match the music playing!
DBS-brain interactions
DBS is intended to interact with neurons that carry electrical signals deep within the brain. Neurons 'fire' (carry an electrical charge to the next neuron in their path) when they reach their electrical trigger point. A DBS pulse will cause a neuron to fire if it delivers sufficient electricity to cause that neuron to reach its trigger point.
A DBS pulse will weaken as it passes through the brain; the further a neuron is from an electrode contact, the less likely the pulse will cause a neuron to fire. Increasing the electric current and/or the pulse-width will likely activate neurons further from a DBS contact. This space around the DBS contact where neurons are expected to fire due to DBS is sometimes referred to as the volume of tissue activation (VTA). The VTA may be displayed on the neurologist's laptop during programming. Whether a DBS pulse triggers a neuron within the VTA also depends on factors such as the orientation and diameter of the neuron's fibre (axon).
The frequency of the DBS pulse (i.e., the number of pulses per second) also has an impact on the therapeutic outcome of DBS. The impact of DBS frequency does not appear to be as well understood as the impact of current and pulse width.
The above summary is intended to introduce some DBS concepts and does not describe how DBS interacts with the complexity of the human brain. Indeed, science is yet to fully explain how DBS supports Parkinson's disease symptoms. This is important to note — if we do not know exactly how DBS supports Parkinson's symptoms, we probably will not know when DBS settings have been optimised for an individual.
DBS programming
Programming a DBS device involves choosing the current strength (milli-amperes), pulse-width (micro-seconds), and frequency (hertz) per contact. By choosing which contacts to use the direction of the DBS pulse can be controlled. Such a combination of settings constitutes a DBS program. A reasonable objective would involve finding a DBS program that supports symptoms as well as the best medication-on state pre-DBS, without the debilitating fluctuations associated with medication.
Different methods are employed with DBS programming. For example, some neurologists will activate the device the day after surgery, others will wait several weeks after surgery to allow any short-term 'stimulation' from the surgery to resolve. When DBS programming commences, the neurologist may activate one contact at a time, and slowly increase the current to identify therapeutic benefits and unwanted side-effects per contact. Such a process is normally conducted without varying the frequency or pulse-width; they may be set to 130 Hz and 60 µs, or something similar.
To measure the impact of varying DBS settings, the doctor will observe the DBS recipient undertaking various tasks. For example, repeating a short sentence to test speech, and walking along a corridor to test gait. These observations are limited to a relatively short period during DBS programming clinic. Problems may arise after clinic as the impact of DBS settings on some symptoms may take many hours to have an effect.
If a good outcome is not identified by the selection of contacts and current, the pulse-width and frequency may also be varied. The polarity may also be reversed, with the negatively charged therapeutic pulse replaced with a positively charged therapeutic pulse. Medication will also be adjusted in addition to DBS program changes.
The concept of the total electrical energy delivered (TEED) per second is sometimes considered when setting DBS parameters. Attempting to minimise TEED is a sensible consideration, especially if the pulse generator does not have a rechargeable battery. TEED is not recommended as a guide to parameter setting. For example, to keep TEED constant, a small increase in pulse width could be balanced by decreasing the frequency by the same percentage; however, DBS current, pulse width and frequency have different impacts in the brain and cannot be simply interchanged.
Figure 4:Example of a dual-frequency program using 5 of 16 contacts. Author supplied.
Suggestions for people with DBS
DBS has significant therapeutic benefits for many PwP, but its interactions with the brain are not yet well understood. Some recipients of DBS may need to be highly proactive to secure the benefits of DBS. Given the resources expended to design, construct and implant DBS devices, and the risk people take to receive DBS, additional effort devoted to DBS programming is a reasonable request. The following suggestions may help you to engage during DBS programming, and demand that greater effort be devoted to programming your DBS device:
- "-At the commencement of a DBS programming session, ask the neurologist to explain the strategy they will employ that session to identify a DBS program with a greater therapeutic benefit.
- -Between clinic reviews, record the impact of different DBS programs on your symptoms. For example, record videos of moving or speaking, or the time required to complete set tasks. Such records may assist in reporting to your neurologist the impact of DBS outside the clinic environment.
- -Maintain a record of the settings for each DBS program prescribed. Just as one can discuss Parkinson's medication at a local support group, this enables discussion of DBS programs in a similar manner. Such information also provides a mechanism to check that the intended DBS settings have been programmed
- -DBS systems typically have a mechanism to allow the recipient to switch between programs pre-set by the neurologist. When leaving DBS clinic, ensure that the best program for you upon entering that clinic is still available. If the impact of new DBS settings only becomes fully apparent after leaving the clinic, it may be helpful to revert to that previous program." [1]
References
[1] McAuley MD. Deep brain stimulation for Parkinson's disease: A case for patient empowerment. Brain Stimul. 2023;16(1):97-99. https://doi.org/10.1016/j.brs.2023.01.840
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