2. Background: EEG and tDCS
● Electroencephalogram (EEG)
○ Measurement of electrical
activity in brain
○ Surface electrodes placed on
scalp
○ Freq: 1-100 Hz
● Transcranial Direct Current
Stimulation (tDCS)
○ DC Current applied to the brain
through electrodes
○ Modulates cortical excitability
Higgins (2008)EEG 10/20 Electrode Placement Diagram
3. Clients
• Dr. Franklin Amthor
• Interim Director of Behavioral
Neuroscience Graduate Program
• PhD. Biomedical Engineering
• Original idea for simultaneous, same-site
recording during tDCS stimulation
• Dr. Mary Boggiano
• Associate Professor of Psychology
• Studying effects tDCS on cravings
• Currently using TCT tDCS Stimulation Kit
• tDCS Only
• Behavioral Feedback
Dr. Amthor Dr. Boggiano
4. Design Need
• Transcranial Direct Current Stimulation (tDCS)
• Possible treatment for many various neurological conditions
• Depression
• Anxiety
• Binge-eating
• Physiological effect with respect to neurological conditions
not well understood
• Current pharmaceutical treatment isn’t always effective and
has many unwanted side effects
Picture?
TCT tDCS Transcranial Stimulation Kit - $349
12. Validation
• Comparison
between signals
acquired with a
commercial EEG
(Grass) device
and our circuit
Figure 2: PSD plot of signal acquired with Grass EEG machine (right)
and our (NeuroVolt) EEG circuit (left).
Figure 1: Raw EEG signal acquired from NeuroVolt EEG circuit (red) and Grass
7D Polygraph (white).
13. Future Work
• tDCS voltage changes with
perspiration, movement, etc. &
causes change in voltage.
• Some AC Noise from 1 to 18 Hz
• Project is being further
developed by Dr. Amthor’s lab
for use in Dr. Boggiano’s lab
Figure 3: PCB Layout for our EEG circuit w/ AC Coupling
14. Acknowledgements
• Dr. Amthor
• Dr. Boggiano
• Dr. Eberhardt
• Dr. Dobbs
• Mary Katherine Osborne
• Carl Stephens
• NIH, NSF, and
VentureWell grants
Editor's Notes
Undergrad Capstone Design
Current EEG (electroencephalogram) + tDCS combination devices
Cost upwards of $10,000.
Not practical for most researchers/clinicians
None provide simultaneous, same node stimulation and recording
For our device we wanted to provide same-site simultaneous EEG and tDCS while maintaining a much lower price point than the competitors. We planned to make this an add-on to the tDCS our client was already using, again pictured here, so that she could use it in her clinical trails without having to go through as much paperwork.
Targeted Users:
Researchers conducting clinical research
Validate and improve tDCS applications
Determine efficacy of tDCS as a therapy for more neurological disorders
and optimize treatment protocols for these disorders
Our constraints fall into 3 main areas: safety, ease of use, and efficacy of the device. Safety mainly consists of ensuring that our add-on does not interfere with the commercial TCT tDCS our client had. For ease of use our client specifically requested minimal electrodes. And of course we wanted limited interference between the systems to our EEG data will be reliable. BUDGET OF $1000
TCT tDCS:
Ramp up/down capability (.5-2mA) - Prevents phosphenes
2mA max amperage
Current flows through cranium from Anode to Cathode
EEG Addon:
Two electrodes – Same as TCT tDCS electrodes:
Anode will be concurrent EEG and tDCS
Cathode will be just tDCS (but can be modified for use with EEG in future)
Gain: ~33,295X
1-100Hz Bandpass filter
60Hz Notch filter - filters background electromagnetic noise produced by nearby electronics
We stayed way under budget even including the cost of the tDCS system we already had. This lists omits some things like copper tape, saudering equipment, and wires which we had on hand and didn’t have to buy specifically for this project. However we anticipate that most research labs will also have access to this sort of equipment.
Because our client wanted minimal electrodes we decided our
Anode will be concurrent EEG and tDCS
Cathode will be just tDCS (but can be modified for use with EEG in future
On the right you see our final prototype, which was very much still a prototype.
Here are our electrodes including the smaller reference EEG electrode. We used an Ethernet cable to combine cords back to the circuit.
This baker’s circuit is our EEG filtering circuit, which Aaron will talk more about in a minute, and it feeds data to our Arduino over here.
Qs:
why reference smaller? It’s what we had. Most likely will get bigger in future prototypes.
Why not just plug into our computer ADC? Wanted to be more portable and battery powered. They use this in multiple rooms every day and don’t have an outlet in one of the rooms.
Simple switch to start collecting EEG data, which could be replaced with a timer or a moving average of the tDCS voltage that triggers collection when it remains stable for long enough.
Since our EEG was wired in with voltage oscillating around 0 we needed a voltage offset circuit so our analog to digital converter, the ADS1015 from adafruit, would not be compromised. We also used constant current diodes to bleed off any current above 5 volts.
We liked the Arduino because it was very well documented and easy to use, but also because it has dedicated clock and data pins which we thought would be better for collecting EEG data.
However, we found that the tDCS voltage is not always constant. The resistance of the electrodes changes slightly as the subject moves or perspires, resulting in a jump in voltage as the current is driven back to 2mA, which causes noise from 1 to 18 Hz.
