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This author here is not a physician, but a physicist.   The last three letters are different, just the last three letters, but what a difference do these three final letters make... Difference on the paycheck, yes, which is important for the Americans, and also a difference on our approach to life, which is what matters to me.   Different language, different approach to knowledge.   Also, this author here was a professor (now retired), not required to follow rules and regulations.   This is particularly true for the physics types, like me..., and even more so after retirement, as, after all, if it was difficult to fire me when I was a tenured professor, it is now even harder to do so, now that I am retired...  

To forestall the reader to becoming annoyed by some explanations of the obvious, they will occur in the following text because we are writing for three types of readers, each with their own background: medical professionals and biologists, physicists and layman.   So, dear reader, when starting a paragraph that is obvious to you, please just skip it.  

We introduce here a new class of electrodes, which we call passive electrodes .   The objective, our ultimate goal, is to control the motion of the electric charges through the bodies of animals.   The application is on electrical stimulation, as in cardiac pacemakers, Deep Brain Stimulation (DBS), and more similar cases.   These electric charges are ions, not free electrons , as they travel through the body of the animal.   Though the following is elementary to physicians and biologists, etc., it is not necessarily clear to layman, so sorry bio guys, for writing the obvious.   I request the reader to keep in mind that the electric charge carriers for at least most, and likely for all electrical currents in the body of animals, are ions, not free electrons.   Free electrons in copper wires travel at approximately 200,000 km/s, or 2/3 of the speed of light in vacuum, which is approximately 5 times around the equator of our home planet Earth in one second, while the ions carrying the electric current that drives the heart contraction travels at approximately 1 m/s, which is 200,000,000 times slower than the speed of the free electrons in copper.   While free electrons propagating in copper wires go 5 times around any great circle around our planet earth in one single second, the ions, propagating in our bodies, take 1 year and 3 months for one single trip around any great circle, or 6 years and 4 months for the same 5 times around that the free electrons swallow in 1 single second!   The ions, which are the electric carriers of the electric currents in our bodies propagate reeeeeeeealy slow!

This said, the author is aware that there are differences in speed of propagation of electric charges between ordinary muscle cells and neurons, and I am kind-of sure that the cells that make the His bundle, the left and right bundles, and the Purkinjie bundles, all in the heart, are capable of conducting electric currents faster than the 1 m/s value used above - but I do not know how much faster, but only that it is not even 10 times faster, which means that it is not a big deal, that the propagation speed even in these special cells is still slooooooow.

Though our general objectives include all the cells, the main cells we are are currently concerned and interested are brain and heart cells, that is, neurons and muscle cells.   Our goal is to control the speed and direction of the ions as they move along each neuron, as in the brain, then from this initial neuron to other neurons, part of the first neuron network, which motion is the physical basis of all brain and motor activities, or the speed and direction of the ions in the heart, as they move along the heart's muscle, causing the progressive contraction of the heart, which is how the peristaltic pump that is the working of the heart. Then, we are also interested in the propagation of electric signals through the spinal cord and other neural pathways, and in the propagation of the electric signals through all other cells, particularly muscle cells, as the biceps, in the arm, etc.

I am leaving aside here the reasons for the brain electrical stimulation - even if I do have opinions on it and even when they reasons are important.   We are here only discussing how to perform the electrical stimulation within the accepted frame and objectives as declared by the neurosurgeons and the greedy companies that manufacture the hardware.   We here will focus on the brain stimulators, but much of what is written here for the brain, carries for the heart electrical stimulators as well (heart pacemakers), so the reader is encouraged to take a look at the heart section of this website.   We are suggesting an improvement on the electrical brain stimulators.  

Introductory material for non-medical people and some history of DBS

In case the reader does not yet know it, Parkinson's Disease causes several disfunctions related to lack of muscle control, the worst being perhaps the hand tremor.   Leaving aside here the temporary control of Parkinson's Disease with medicine (Lovadopa), let us limit ourselves here to the surgical control of Parkinson's.   There existed one surgical procedure before 1987 to stop the tremor from the Parkinson's Disease.   The neurosurgeons were back then destroying the brain cells in some selected places to stop the tremor.   This was a most undesirable procedure; can you imagine destroying a bunch of cells in your brain? Mamma mia...   This older procedure of destroying parts of the brain, yes, small pieces, but still ... , was abandoned in favor of the electrical stimulation introduced by the French neurosurgeon Alim-Louis Benabid in his medical practice in France in 1987.  

Introductory material for non-medical people and some history of DBS - continuation

Another last piece of information for the layman, is that the brain is compartimentalized, much as a company's building or a private home are, with sectors reserved for certain tasks, as, for the brain, motor control, or decision-making, or visual processing, or auditory processing, etc., or, for companies, an area for the bookkeeping, perhaps spreading through more than one room, another for the shop and construction, another for the bosses, etc, or, for private homes, if large family, an area with one or a few rooms for the children, an area for mom-and-dad, another area for guests, in the United States, an area for the video games, in Brasil, an area for the library, etc. etc.

The neurosurgeons discovered the locations of the small portions of the brain that are involved with the Parkinson's tremor, so that they can go there and destroy them (before 1987), or add an electrical stimulation (after 1987) that distracts them cells, causing a cessation of the tremor while the electrical stimulation is on.   But there is a catch here, for the brain.   While the room(s) used by the bookkeeper(s) is separated from the room(s) used by the bosses by rigid, solid walls, this is not the case for the small sections of the brain that work for each different function; the sectors of the brain that are dedicated to various types of tasks are continuous throughout the whole thing, there are no separation between the brain regions, no walls, no fences, no delimiters.   It is this lack of walls that is the reason for the improvements we are proposing for the picafinas - and for the heart pacemakers as well, mutatis mutandis .  

Introductory material for non-medical people, word definition - continuation

For their reason, it is the practice of the neuro guys to use the word "area" for what everybody else would say "volume".   So, when a neuro guy speaks of the "visual area", or the "auditory area", etc., what they are meaning is the volume, in the brain, which is responsible for the visual process, or responsible for the auditory process, etc.   Don't ask me why; I am not neuro.   We will use both forms, area and volume, because both types may read this, often referring to the other, alternative form.  

Some history of DBS, continued

The French neurosurgeon Alim-Louis Benabid, working in his home country France, originated the era of electrical brain stimulation.   Benabid discovered in 1987, while working as a neurosurgeon in his home country France, that when what is called high-frequency electrical stimulation was injected into some places in the brain, then the hand's tremor disappeared, and other motion symptoms as well.   High-frequency for them neuros means f =~ 100-140 Hz, including a little higher, with a on-time of around 100 microseconds.   The electrical stimulation is not a sinosoidal, not at all, but rather it is what is known in electronics as a square wave but with a short on time, making it a small duty cycle, using the EE words.   This is a very small duty cycle of around 1% (1% on / 99% off).   The new solution developed by Banabid was to implant a small, thin supporting structure from the top of the skull, the tip of which was inserted down into the base of the brain, this supporting structure being fitted with four cylindrical electrodes near the tip end, from where the electrical stimulation can be inserted at some precise locations at the base of the brain.   The supporting structure was, and the current models still are, thin cylinders approximately 1.3 mm (1/16 in) in diameter and 10 cm (4 in) in length; I call them "picafina", a word from Latin origins that means a small, thin penetrating device, while Medtronic called them "lead" - Americans are not familiar with Latin.   Banabid's new solution required to maintain this stimulating electric current of 100 microseconds-on pulses every 10 ms continuously forever and ever.   This was introduced late 1980s, when the technology for battery operated stimulators was already solidly developed for heart pacemaking, so the technological basis for Banabid's solution to the Parkinson's Disease was available.   If the electric stimulation is interrupted, then the Parkinson's Disease tremor starts again within minutes or even seconds after the interruption.   I have seen this, it is impressive.  

This here is the end of a picafina (called "lead" by Medtronic), inserted in some of the intended target volumes, with the target volumes marked in color yellow and the reach of the electrical stimulation in red.   Note that the target location is barely larger than the electrodes and the diameter of the picafina, which is expected to be placed at the center of the target, at the base of the brain, unseen by the neurosurgeon.   The electrodes are 1.5 mm high, 1.3 mm in diameter, approximately the size of a grain of rice. (A) and (B) depict the stupid Medtronic picafina, and (C) depicts a post-Medtronic picafina implanted mostly off-target but able to correct for the non-ideal implant position.  

The only hardware available for Deep Brain Stimulation for Parkinson's Disease until recently, was manufactured by Medtronic, which came in two virtually identical variations.   One of the problems that plagued the picafinas (called leads by Medtronic) was that both target locations are rather small, and at the base of the brain, unseen by the neurosurgeon who was implanting the picafina (or lead, as Medtronic calls it) from the top of the head, the only visually accessible location.   If the neurosurgeon implanted the picafina at the ideal target location, as in (A) figure 1 above, than the stupid Medtronic picafina worked fine.   But if the neurosurgeon did not implant the picafina exactly at the center of the target location (B in figure 1 above) - location which he could not see, then the stimulator would be unable to electrically stimulate the full target volume and/or stimulate non-target brain cells, causing what Medtronic named "side effects", their euphemism (B in figure 1 above).   This was so because for a picafina implanted as in B figure 1 above, the stimulation requires an asymmetrically distributed stimulating volume, which the stupid Medtronic picafina cannot do.   This point being important for the case, let us repeat it here from a different point-of-view: since all the Medtronic's devices were cylindrically symmetric, whenever the electric stimulator were inserted off-center on the target volume, it was impossible to electrically stimulate all the target volume - given that for a not-at-center implanted picafina, the edges of the target volume were at different distances towards different directions.   The stimulation being cylindrically symmetric by necessity, when the picafina is inserted closer to one side than to the other of the small target volume, then either the strength of the injected electric current is limited to not go beyond the nearer border, in which case the farthest border is never stimulated, and with it, some part of the target volume is never stimulated, or else the strength of the injected electric current is adjusted to reach the furthest border, in which case the injected electric current would go beyond the nearer border, therefore stimulating unintended parts of the brain.   When the first option is chosen, then the tremor may not be completely, or well, controlled, while when the second option is chosen, some unintended result, linked to some brain activity just beyond the nearer border of the target volume, and not related to the tremor, was likely to appear, and these were called "side effects" by the neurologists.   The point here is that most electrical stimulations in real life must be compatible with devices implanted off-target location.  

Comparing the stupid Medtronic picafina with the post-Medtronic picafina

Figure 5 below, split into three pages, 5a, 5b and 5c, for three different locations of the picafina within the target volume, displays the reach of the electrical stimulation caused by the old, stupid Medtronic picafina, compared with the new, segmented one, inside a typical target location, which is always a contorted, irregular volume.   For simplicity figure 5 displays a cross section at an arbitrary height, instead of a 3D photo-style display.   Though I am showing a 2D cross-section simply because it is easier for me to draw this way, the matter of fact still is that a simplification is generally better for the understanding of the subject than a photo or even a photo-like depiction, or even a very detailed drawing or depiction, because the simplified drawing takes out the unimportant details, leaving only the essential for the mind.   In other words, a simplified 2D depiction, of the type I am using, is more informative for the brain (no pun intended...) than a 3D realistic drawing, or a photo, though a 3D realistic drawing is better for the eye than the 2D simplified cross-section.   This is so for the same reason by which a good caricature is often a better display of someone - for the mind - than a standard photo of the same person: the caricature extracts and displays the essencial of the subject.   Americans prefer the realistic representation, preferably with vibrant colors, while I elect to speak to the mind and prefer a 2D simplification.

Figure FIG5a above displays the ideal case when the picafina is inserted at the perfect ideal location inside the target volume, inserted right at the center of the target location - a most unlikely event, an event that occurs more by luck, then by skill of the nerosurgeon.   For this perfectly implanted picafina, the segmented picafinas are not much better than the former stupid Medtronic picafina, which found buyers because there was no choice, likely due to patents owned by Medtronic.   Then FIG5b and FIG5c below show two possible implant possibilities, at two locations, inside the target volume, but not at the dead center of the target volume.   The top, b1 and c1, displays the stimulated region with the Medtronic Stupid Picafina, while the botom displays the stimulated region with the Post-Medtronic Picafina.   The reader will notice that the stupid Medtronic picafina would electrically stimulate non-target volumes, with what Medtronic calls by the euphemism "side effects", while the post-Medtronic Picafina at the bottom, implanted at the same location, stimulates only the intended volume, no "side effects".   The reader will appreciate that the choice of which electrode to activate is made post-implantation, depending on the location that the picafina actually is, inside the target volume.   The neurosurgeon cannot be perfect, but he can choose which electrodes to activate post-surgery, to obtain the perfect stimulation!   But NOT with the stupid Medtronic device ... :(  

The reader is here reminded that the diameter of the picafina is 1.3 mm, and the dimensions of the target volume are ... uhhh ... 2 mm along some direction, 3 mm along another direction, etc., all a little, but not much, larger that the diameter of the picafina.   As discussed above, the target volume is deep down the brain, unseen by the neurosurgeon, which is the reason why only by luck can the neurosurgeon insert the picafina at the bullsEye, at the center of the target location, as in FIG5a.     Then FIG5b and FIG5c show two possible scenarios, with the picafina still inside the target volume but not at the BullsEye.   FIG5b displays the picafina placed in a most unfortunate location, inside the target volume, but at a side pocket of it, and FIG5c displays the picafina placed also inside the target volume, at the edge of it.   Since figure FIG5a displays the picafina at the bullsEye, there is no reason to make two figures, one figure with the, using my words, "stupid Meditronic" picafina and another figure with the newer, segmented picafina, introduced by other and better companies.   For a perfectly implanted picafina, the old, "stupid Medtronic" picafina would do the job.   Then figures FIG5b and FIG5c show what is the situation on the majority of situations, when the picafina is anchored out from the bullsEye.   The reach of the electrical stimulation is shown in all cases.   The reader is here reminded that the actual reach of the electrical stimulating charges is not actually fixed, but depends on the chosen electric potential (voltage as the Americans call it), so, the reach displayed in all these cases is an arbitrary choice.   All along, the main information here is the selective directional electric stimulation, independent of the actual reach, but only the result of the possibility of injecting the electrical stimulation towards some, and not all, directions.  

The passive electrodes receive its name from the fact that they do not need energy of operate; they are, therefore, of the same class as the resistors, or the capacitors, or the inductors, none of which requires any source of external energy to do their job.  

The passive electrodes are the modification / enhancement that I am adding to the electrical stimulation with the objective of applying a force on the injected electric charges, with the ultimate objective of keeping the injected electric charges along some preferred path.   This force, which is explained below, affects both the direction and the speed of the electric charges as they move through the animal - perhaps a brain, perhaps a heart, etc.   Or, repeating myself, the objective of the passive electrodes is cajole the injected current into a path that goes through the intended cells that the medical person wants to electrically stimulate - and not through other cells.  

The passive electrodes are physically similar to the ordinary electrodes, which I call active electrodes, with the difference that the passive electrodes are covered by an electrically insulating layer, which prevents any electric charge to leave the electrode.   Keep in mind though, that the electric field penetrates through the electrical insulator!   The electric charge does not penetrate, but the electric field penetrates!   An interesting example, if the reader gets puzzled by this statement, is the floor where the reader stands right now, or where the chair in which the reader sits is planted.   The gravitation goes through the floor, else the reader would float as the astronaut floats in the space station, though the floor prevents the mass (the reader, the chair, etc.) from moving toward the earth.   The floor is a gravitational insulator for the property in question, the mass, as much as the electric insulator is an insulator for the property in question, which is the electric charge.   So dear reader, don't worry about the electric field: the electric field does penatrate through the electrically insulating layer deposited on the outer surface of the passive electrodes.  

Since the passive electrodes do not inject any electric charge into the surrounding environment, it follows that they, the passive electrodes, can be continuously energized.   This is wonderful for two reasons: (1) because their effect on the injected electric charges, unlike the effect of the active electrodes, is on all the time, and (2) they, the passive electrodes, do not drain energy from the battery, which is a precious device in an implanted device, because one does not want to open the patient again to change the battery. Regarding the first point, that the passive electrodes are energised all the time, the reader is reminded that for DBS the typical duty cycle of the active electrode is of the order of 1%: 0.1 ms on, followed by 10 ms off.  

Besides the above advantage, the passive electrodes offer two more advantages over the active, or normal electrodes.   Firstly, the passive electrodes can be located below the outer surface of the supporting device - that is, under, below the active electrodes.   Indeed, since the passive electrodes do not inject any charge into the body, they do not need any physical contact with the body, say, the brain or the heart, or any other organ.   This is advantageous because the space at the surface of the supporting structure is limited, and needed for the active electrodes, which can hardly afford to share the space, as such sharing would limit the locations, and therefore the directions, from which the electric charges can be injected.  

Secondly, the passive electrodes can be constructed with the technology used to construct supercapacitors, which is that the surface of the capacitor's plate is populated with a large number of cavities, and smaller cavities inside the first cavities, and even smaller cavities inside the second cavities, and so on - a very porous surface.   It is the surface porosity that increases the surface area, allowing for a larger electric charge to be stored, and consequently a larger capacitance C for the supercapacitor application, and a larger electric charge Q for our passive electrode application. The increased electric charge Q, in turn, increases the electric field in the space around the passive electrode, and consequently increases the force on the stimulating electric charge that is injected by the active electrodes.   This technology is well developed, because of the earlier need to make capacitors with larger capacitance, therefore it is easy to include this feature into the passive electrodes.   It offers the advantage of storing more electric charge Q, for the same electric potential available from the battery, which, in turn, is advantageous because the electric field produced by any device is a linear function of the electric charge of the device in question.   It is known that the supercapacitor technology can increase the area of the capacitor's plate, and therefore the stored electric charge, for a given electric potential, by a factor of 100,000 (one hundred thousand).   Consequently, it follows that the passive electrodes are capable of projecting electric fields 100,000 times larger than the electric fields projected by the active, or traditional electrodes - a respectable increase in the force applied to the electric charges injected by the active electrodes.   Preferably all the passive electrodes would be below the surface, since they can be there, in order to save real estate for the active electrodes at the surface.  

Butson and McIntyre (from the Cleveland Clinic Foundation) published in 2006 an article in which they describe the results of a computer calculation of the consequences of the electrode design on the (electric) field shape of the region receiving electrical stimulation.   Note that this was back in 2006; it was already well known how to improve the picafina, it was well known what was needed for the benefit of the patients, and Medtronic knew it.   Butson and McIntyre calculated the result of changing the dimensions of the supporting wand (that is, the thin, drinking straw-like structure that is implanted in the brain, which Medtronic calls “lead”) and electrode (that is, the ring-like conductive surface at the extremity of the implanted lead), but they did not consider the possibility of asymmetric field shapes, let alone the possibility of changes on the electrode shape after the surgery is completed and the lead fixed in place.   Most likely such changes were not contemplated by the authors because they could not image it physically possible to depart from the Meditronic lead design: a long cylinder with four ring-like electrodes at the end.   Butson and McIntyre’s calculation is limited to this constraint.   Even with this limitation they show how a smaller diameter lead and long electrode could fit better the needs of a particular patient.   Butson and McIntyre’s calculation is useful as an indication of the medical consequences of lead and electrode design on the stimulated area, even though their calculations were not carried to the ultimate consequences of asymmetrical fields.  

Their article does not go to the ultimate advantages, which are asymmetric fields and post-surgery choice of field shape, that is, to create an arbitrary volume shape after the lead is fixed in place, also adapted to the particular positioning of the lead within the desired volume, both to correct for failure to insert the lead exactly on the target area, and to inherent locus asymmetries, possibilities that exist with the adoption of our invention, but not with current devices.   Click here to see Butson & McIntyre Field Simulation

In this article, Kenneth Follett et al. publish the results of their statistics on side effects of DBS.   The side effects probability depends on the implant locus, which in this study is either the globus pallidus interna (GPi) or the subthalamic nucleus (STN), and Follett’s article contains both numbers, separated for each locus and consequences.   Depression frequency runs from 26% (GPi) to 37% (STN), speech problems frequency runs from 28% (GPi) to 35% (STN), and confused states frequency runs from 20% (GPi) to 22% (STN), for each, respectively (table 4, page 2088). Click here to see Kenneth et al. article  

A more recent review article is Michelle Paff et al . "Update on Current Technologies for Deep Brain Stimulation in Parkinson’s Disease", J Mov Disord. 2020 Sep 1;13(3):185–198. doi: 10.14802/jmd.20052.   Michelle Paff and co-workers give a good review in it, worth reading. They analyze the differences between the stupid Medtronic picafina and the post-Medtronic ones, offering directional stimulation, and show the advantages of the post-Medtronic devices.   Click here to see Michelle Paff et al. article  

Anoter recent review article is by Erin Patrick et al . "Modeling the volume of tissue activated in deep brain stimulation and its clinical influence: a review", in Frontiers of Human Neuroscience, published 10 April 2024, DOI 10.3389/fnhum.2024.1333183.   Erin Patrick and co-workers make a good review of the consequence of the fraction of the target volume that is actually electrically stimulated, and also the volume that is electrically stimulated but are not intended to be so. It is worth reading.   Click here to see Erin Patrick et al article  

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