Category Archives: Neurostimulation and Neuromodulation

A 0.042 mm^2 programmable biphasic stimulator for cochlear implants suitable for a large number of channels

ArXiv-paper on miniature neurostimulator circuit

Today we published the following (scientific) paper online:

A 0.042 mm^2 programmable biphasic stimulator for cochlear implants suitable for a large number of channels
W. Ngamkham; M.N. van Dongen; W.A. Serdijn; C.J. Bes; J.J. Briaire; J.H.M. Frijns; 
ArXiv.org
January 29 2015. 

Abstract

This paper presents a compact programmable biphasic stimulator for cochlear implants. By employing double-loop negative feedback, the output impedance of the current generator is increased, while maximizing the voltage compliance of the output transistor. To make the stimulator circuit compact, the stimulation current is set by scaling a reference current using a two stage binary-weighted transistor DAC (comprising a 3 bit high-voltage transistor DAC and a 4 bit low-voltage transistor DAC). With this structure the power consumption and the area of the circuit can be minimized. The proposed circuit has been implemented in AMS 0.18µm high-voltage CMOS IC technology, using an active chip area of about 0.042mm^2. Measurement results show that proper charge balance of the anodic and cathodic stimulation phases is achieved and a dc blocking capacitor can be omitted. The resulting reduction in the required area makes the proposed system suitable for a large number of channels.

Keywords:

current generator, current source, current mirror, output impedance, stimulator
circuit, current stimulator, programmable stimulator, biphasic stimulation, neural stimulation, cochlear implants, electrode-tissue interface, electrode-tissue impedance, switch array, charge error, charge balancing, neurostimulator.

Laagfrequente tinnitus

Foto en artwork: Marleen Serdijn

Foto en artwork: Marleen Serdijn http://instagram.com/marleen.serdijn/

Vandaag ontving ik een email van een lezer van de Bioelectronics weblog, met daarin de vraag of neuromodulatie ook zin heeft in de behandeling van laagfrequente tinnitus, d.w.z., tinnitus die zich manifesteert als een gebrom of gezoem in plaats van een hoge (fluit-) toon.

Hieronder een deel van mijn reactie aan deze lezer, in de hoop dat het ook nuttig kan zijn voor andere mensen die lijden onder tinnitus.

Beste [afzender van de email],

(…)

Voor zover ik heb begrepen is tinnitus potentieel goed te behandelen indien het zijn oorsprong vindt in de gehoorschors en zich nog niet erg lang manifesteert (minder dan een paar jaren). [Prof.] Dirk de Ridder [verbonden aan het St. Augustinus Ziekenhuis in Antwerpen] en zijn team onderzoeken hoe ze de structurele verandering van de gehoorschors, bijv. ontstaan als gevolg van een gehoortrauma (bijvoorbeeld luid geluid), ongedaan kunnen maken door neuromodulatie, al of niet vergezeld van andere vormen van stimulatie. Of de tinnitus hoog- of laag-frequent is maakt volgens mij niet fundamenteel uit. Het kan wel betekenen dat de tinnitus een andere oorzaak heeft en dus anders “in de hersenen geprogrammeerd” en daarmee minder goed te behandelen is. Er is bijvoorbeeld een vaak voorkomende relatie tussen gehoorverlies en het optreden van tinnitus.

Als technisch wetenschapper probeer ik verbeterde technologie te ontwikkelen die de neurowetenschappers en neurochirurgen in staat stelt betere behandelingen te ontwikkelen, die minder invasief is en zich automatisch aanpast aan de therapeutische behoeften patient.

Ik hoop dat u iets aan het bovenstaande heeft.

Met vriendelijke groet,

Wouter Serdijn

Wouter A. Serdijn, PhD, F-IEEE, DL-IEEE Head Section Bioelectronics

Delft University of Technology Faculty of Electrical Engineering, M&CS Mekelweg 4, 2628 CD Delft The Netherlands Phone/Fax: +31-15-278-1715/5922 Email: w.a.serdijn@tudelft.nl serdijn@ieee.org http://elca.et.tudelft.nl/~wout http://bioelectronics.tudelft.nl

Injectable Electronics: dawn of a new era in electroceuticals?

Injectable electronics still need to become smaller

Frequent readers of this weblog may still remember a previous post, entitled “And the paralyzed will walk again“. This phrase comes from a Discovery Channel movie/documentary, called “2057: the body”, in which it is predicted that by the year 2057 you will be able to survive a three story fall and even be able to walk again as there will be tiny microstimulators attached to your muscles, which can be injected.

Injectable electronics, how fascinating would that be! No more lengthy surgeries, during which only a single, bulky device is implanted, but rather a procedure that takes less than a couple of minutes, during which multiple micro-stimulators are inserted via a seringe. Once done, these stimulators will form a wireless network and will provide the motory neural pathway with well-timed electric stimuli necessary to evoke the correct contraction of the multiple muscles involved in a delicate movement or even seemingly simple posture control.

But how feasible is this idea of injectable electronics? If you search for the term injectable electronics, you will most likely find a lot of references to the work of John Rogers, professor at the University of Illinois in the US, who built “an electronic LED device so tiny it can be injected into delicate tissue, such as in the brain, without harming it“.
Other links that can be found refer to work done on silk implants or even magnesium implants that are either stretchable or can easily dissolve into the body once the good work has been done.

I personally believe that we only can create injectable electronic devices if they have at least some intelligence in them. For this, the good old silicon would be an excellent candidate. Silicon is a nice and friendly biocompatible material, can be made bendable (by thinning the substrate) or stretchable (by removing the substrate altogether at some points). And what’s more, silicon can accommodate stimulation circuitry, sensors, signal processing, communication electronics, antennas, battery foils, all the good stuff needed to make a good injectable.

Of course, in order not to damage the tissue that the electronic device is injected in, it needs to be small, i.e., thin and narrow. It is however allowed to make it long, e.g., a couple of millimeters up to one or two centimeters. These unconventional dimensions raise very exciting technological challenges, such as:

  • how can we create electronic integrated circuits (ICs) that are merely one-dimensional, i.e., are not wider than one, maximally two, bondpads?
  • how can we transfer information and energy to an implant that has virtually no area?
  • what kind of material should we use for the antenna and electrodes?
  • will a Li-Ion battery foil have enough capacity to provide successful stimulation of the tissue, or should we refrain from using batteries altogether?

There obviously is still a lot to do. Exciting stimes ahead, if you ask me.

Wouter

A new name, but Biomedical Electronic remains

Biomedical Electronics Lab

Dear Reader,

The Biomedical Electronics Group underwent a small name change. From now onwards, the group is called “The Biomedical Electronics Laboratory”.

Its mission is “to provide the technology for the successful monitoring, diagnosis and treatment of cortical, neural, cardiac and muscular disorders by means of electroceuticals.”

To this end it conducts research on, provides education in and helps creating new businesses in neuroprosthetics, biosignal conditioning / detection, transcutaneous wireless communication, power management, energy harvesting and bioinspired circuits and systems.

Aside

At the annual general assembly of the Delft Research Center on ICT (DIRECT), we proudly presented one of TU Delft’s faculty flagship projects “Beethoven”. Beethoven is a technology-driven research project on electroceuticals that aims at the design of a flexible brain … Continue reading

Quote from Michael Merzenich

While reading, correcting and enjoying the essay of Jose Manuel Rosas Escobar, I stumbled on a quote from Michael Merzenich, which I think you should read and comtemplate on.
So here goes…
“The success with any complicated prosthetic device relates as much to how the brain adjusts to it, accepts it and controls its use as it does to the device itself. If we can figure out how to engage the brain to do its part, it can make a merely adequate neural prosthetic device work marvelously.”

Wouter

Neurostimulation causes nerves cells to grow back and allows paralyzed to walk again

Article from De Volkskrant, dd. Oct. 27, 2012, entitled "Paralyzed walks again"

Article from De Volkskrant, dd. Oct. 27, 2012, entitled “Paralyzed walks again”

Eddy was damn right when after the disk in his spinal cord was removed by the neurosurgeon and he lost almost all the feeling in one of his legs due to the acute hernia. By means of transcutaneous stimulation of his foot and leg he was able to regain feeling and control over his muscles  and walk again. The method was not proven scientifically yet, but obviously worked, as we witnessed from closeby. Now the scientific proof is there.

Exciting times ahead, if you ask me.

Wouter

Mission Possible

In order to present the Biomedical Electronics Group of Delft University of Technology to a couple of companies, it made sense to reveal our mission statement. So here it goes…

The mission of the Biomedical Electronics Group of Delft University of Technology is "to provide the technology for the successful monitoring, diagnosis and treatment of cortical, neural, cardiac and muscular disorders by means of electricity." In order to reach this goal we investigate and design circuits and systems for electrical stimulation, ExG readout, signal specific analog signal processing, power management/conversion, energy harvesting and wireless communication, to be applied in future wearable and implantable medical devices, such as hearing instruments, cardiac pacemakers, cochlear implants and neurostimulators.

So how about that? Reactions are welcome via this blog.

Wouter

Hallucinations

Iris Sommer, Professor in psychiatry at the UMC Utrecht describes in a video at www.volkskrant.nl/akademie a schizophrenic man who told her about the terrible voices in his head. To figure out what happened in his brain during these hallucinations, she made several MRI (magnetic resonance imaging) scans. It turned out that in patients with hallucinations also the language areas in the right half of the brain become active. In healthy people usually only those areas in the left half of the brain are active.

She further explains that these areas and the voices in the head can be influenced in a variety of ways, e.g., by means of TMS, transcranial (through-the-skull) magnetic stimulation. Unfortunately, TMS is not always effective and psychiatrists are on the lookout for alternatives. 

I would say that this is another area where neurostimulation can come to the rescue. In the (often successful) treatment of tinnitus, patients are first exposed to TMS to check whether neurostimulation, in this case, electrical stimulation of the auditory cortex, can possibly be an effective treatment for them. Once indeed the level/severity of tinnitus can be influenced by TMS, neurostimulation becomes a logical next step for permanent treatment of the tinnitus.

Now it is just a matter of convincing the other voices in my head that this is indeed the right way…

Wouter

Future treatment of Neurological disorders: Neuromodulation through Deep Brain Stimulation

In recent years, neuromodulation has proved to be a feasible alternative in the treatment of the increasingly common neurological conditions. This essay describes deep brain stimulation as a treatment option for neurological disorders. First, a brief history of brain stimulation is presented followed by a description of the mechanisms of action and the surgical procedure. The current technology is not perfect and many of the complications which arise from deep brain stimulation are hardware related. These complications can be addressed by the further development of intelligent leads, new power generation methods and a less invasive technique.