The biohack.me forums were originally run on Vanilla and ran from January 2011 to July 2024. They are preserved here as a read-only archive. If you had an account on the forums and are in the archive and wish to have either your posts anonymized or removed entirely, email us and let us know.

While we are no longer running Vanilla, Patreon badges are still being awarded, and shoutout forum posts are being created, because this is done directly in the database via an automated task.

Electrodeless Neuro-Interfaces

Comments

Displaying comments 31 - 43 of 43

JohnDoe

February 2016

How are you optically reading brain waves?
TheGreyKnight

February 2016

edited February 2016

So, when you shine infrared light on a neuron, if that neuron fires, it changes the optical properties of the cell membrane. That change causes it to reflect light differently, allowing you to extract data on the cell's current condition.

If you increase the amount of energy you're introducing to said neurons via infrared light, you can cause them to fire an action potential. I theorize you could effectively combine these technologies by using one frequency of infrared to read and pre-charge the region you'll be "writing" to, and another frequency to increase the total energy in the region to the point that everything fires. You may even be able to use the same frequency for all of it. But if you were pulsing the system on and off, you'd need to account for the spikes in energy.
JohnDoe

February 2016

Can inferred penetrate the human skull? Furthermore could enough of it be reflected back that you could varify a change in brain state? Maybe something like a photo multiplayer tube? Shielding of sensors should be a a bitch. Could run off the some of the same hardware of the ModulerEEG.... Hum I am vary interested now. You may have figured out the key to nural input.... While at the same time makeing a tDCS device 1000x safer....
TheGreyKnight

February 2016

Yes, some frequencies of infrared can penetrate the human skull. According to one of my sources (LINK), "the maximum optical penetration can be estimated to be about 1.5 cm when a detector is placed at 4 cm from the source." (Page 1, Paragraph 4, Line 10)

Very, very important note. There are 2 ways of using this technology. The first is observing the vascular activity in a given region (Changes in the absorption properties of the tissue). This is okay for BCI's where time isn't an issue.
The other option is to use it to observe the neurons themselves (Changes in the way the tissue scatters light). When a neuron fires an action potential, it changes the way it scatters the light nearly simultaneously. This in particular is what I'm interested in. If all the claims in the papers I've found are accurate, this ought to provide temporal resolution comparable to electrocorticography.

I'd be interested to see if it's possible to use technology similar to holography to capture and utilize the data.

Shield the sensors from what? It's just like a camera. Just with infrared light instead of visible light.

What I haven't found yet are trials that use this technology to observe the brain while stimulating it with tDCS, or something similar. So, it's kind of hard to get a feel for how the rate at which neurons fire relate to an EEG signal. So, if anyone's interested in assisting with such a study, let me know. I'll start writing up the procedure for the tests.
JohnDoe

February 2016

So you are not worried about any IR noise messing with you sensor(s)? I will have more questions just not going to ask anything till I read that paper. Sincerely? John Doe
TheGreyKnight

February 2016

I'm still working on an actual design for a sensor array. As far as how I'm addressing noise, I intend to eliminate as much electrical noise as I can. External infrared noise should be very easy to block. Interplay between the sensors in the device could be a problem. I've yet to start tearing apart the finer details of the various set-ups used by the researchers for these experiments.

The first order of business for getting a scatter-based sensor working is establishing all of the variables. Does a change in the oxygen level of the blood through a certain spot change the scattering behavior of that region? How much does the scattering coefficient of a neuron change when it fires?

This study (LINKSOURCE. ARTICLE Shout out again for @ElectricFeel getting ahold of it) goes over and reviews a number of studies on EROS. It mentions the potential of scattering and absorptive, but, unless I've missed something, they don't say outright which of the 2 is being used. I'd really like to get my hands on some stuff to do a quick proof of concept.

In regards to sourcing IR diodes and lasers, do you have a good source for getting diodes that emit IR at 690 nm @ThomasEgi ?
JohnDoe

February 2016

How many do you need and how many milliwatts do you need? Have you seen this: Thorlabs HL6738MG Laser Diode?
TheGreyKnight

February 2016

For proof-of-concept, just one. According to this (LINK), an LED that was only 500 microWatts was sufficient. I'll do a bit more looking, and see if 30 mW is too much. That definitely looks like it might work.
ThomasEgi

February 2016

TheGreyKnight there are many LED's around that wavelength, and almost no lasers at the exact wavelength. You can get 670nm Lasers. If you don't have to use lasers for a very good reason, don't use them. They are super delicate, short lifetime and they pretty much die if you look at them with an angry expression on your face ( got this validated by a number of people working with solid state lasers).
Also, for lasers you can't just scale down power as you'll have the laser threshold somewhere. As for LED's it scales pretty well with current.
As for LED's there's plenty of choice, if you can list me some requirements they have to met I might be able to help you. Deep red can get you as close as 660nm. Ir are typically around 850nm and more.
My workhorse for optical communication systems are the SFH203 (and variants), in combination with regular red led.

As for low-noise design, please hit me on IRC. I got a good share of experience with optical systems/circuits, analog and very low noise designs.
TheGreyKnight

February 2016

edited February 2016
Well, is there a time you're usually on IRC @ThomasEgi ?
And just to make sure I've got it right, #biohack goes in the channel? I'm pretty unfamiliar with IRC.

As far as requirements, something meeting these criteria should do.
- Wavelength: 690 - 1000 nm (I'd prefer to use one below 900)
That frequency range is a must, though. It's the range in which hemoglobin is only a weak absorber of the infrared light.
- Voltage: 3.3 V - 5 V (To work with common microcontrollers)
- Power: 200-300 microWatts as a lower limit for steady light output. I'll say something around 10-20 milliwatts for an upper bound on power
500 microWatts was reported as the "power" of the diode used in the experiment. Whether that was the wattage drawn by the LED during operation, or the energy delivered by the light emitted by said LED, I'm unsure.
- Amperage: Something in the milliWatt range, that's easy to drive and output accurately.
- Lifetime: Not really a crucial stat at this time, but obviously something I can use more than 100 times. I'll probably have it running a pulse for no more than 2 hours.
- View: I'd prefer something that's going to give me a nice, tight beam, but can be modified with a lens to cover a wider area later.
- Mounting style: Through Hole
- Size: Something reasonable. Millimeter scale is preferable.
- Quantity: No more than 50. I'll probably end up using more than 1 LED, but I have no idea what I could do with a bunch of low-power infrared LEDs.
- Style: Single LEDs. Strips of diodes will just be a pain to work with.
- Price Range: Since I'm assuming I'll end up having to bulk order, no more than $5 per diode.
On a slightly different note, are there any reasonably sized alternatives to Solid State lasers that can provide microsecond or nanosecond speed pulses with a fairly high amount of power (300-500 milliwatt range)? Something with a collimated beam, or a beam that lends itself to being collimated would help as well.
ThomasEgi

February 2016

TheGreyKnight, i'm on irc pretty much 24/7, worst case you catch me sleeping.
You'd have to connect to the freenode irc network and enter #biohack. That's all. I suggest using the same nick as on the forum.

As for the diodes.
Best thing that comes to my mind would be the SFH 4550.
It's rated radiation flux for constant output is 50mW if I remember correctly. 850nm. Switching times 10/90 and 90/10 is rated 12ns. If desired it can be pulsed as hell (up to 1.7A if you keep the duty cycle low). Since it's an LED it scales pretty well into the lower-power range. Standard 5mm LED size, sells for about 0.65€ in single quantities, half the price when you order in bulk of 25 or 100. It's not a laser-beam you get but 3° half-angle is about as narrow as an LED beam can get.
As for driving it into ns-pulses I'd recommend to wire up some 74AHC logic in parallel. Following the usual rules for high speed designs. Might help to bypass the diode's current limiting resistor with a small capacitor to clear charge carriers a bit faster out of the diode.

As for matching detectors:
Given the wavelength you may want to use the SFH203-FA variant for receiving (if you don't want to pick up light below 800nm anyway)
BPW 34 would offer you more convenient mounting (it's flat-top) and a quite large sensor area, response time is still at speedy 20ns. Available in both,SMD and THT.
Talking about flat tops SFH203-P offers that ,too. Same price ballpark as the other diodes mentioned.
Getting a signal out of the diodes at such high speeds probably requires more than just 3.3V or 5V. Circuit efforts depends a lot on what you really need to record. Be prepared to use around 30V if you really need to measure those 2digit nanosecond pulses like there's no tomorrow.
TheGreyKnight

February 2016

Odd. I've connected to that channel a number of times and seen nobody on. I'm going to try bypassing my firewall, and see if that's what's causing trouble.
ThomasEgi

February 2016

oh i'm horribly sorry. the channel is ##biohack , in accordance with the freenode channel naming rules. silly little mistake of mine to not notice. See you there :)

Displaying comments 31 - 43 of 43