Summary.
O.D.E. to Lotka-Volterra is an external representation of the Brain-Gut Microbiome interaction that takes place inside humans, where different species of bacteria in the large intestine live in a dynamic ecosystem that communicates with the brain. They send signals to the central nervous system (CNS: brain + spinal cord) to handle the immune system with neurotransmitters and hormones that are key to determine our mood and likelihood to acquire diseases such as depression, obesity or cancer. The gut-brain axis mutualistic relationship determines to a great extent how healthy we are, and its balance is affected, among other things, by our eating habits, stress levels, antibiotics and parasites. Here, a metaphor of this phenomena is made visible by manipulating bacteria with electronic devices in order to approach a Lotka-Volterra behavior.
Background mathematical model.
The so-called Lotka-Volterra Ordinary Differential Equations (ODE) describe the behavior of a predator-prey system, in which a species’ population grows by eating another species. When prey’s population declines, so does the predator’s and then the cycle reverses.
Fig.1: Development of a predator-prey population to first Lotka-Volterra law Author: Curtis Newton ↯ 10:55, Apr. 20, 2010 (CEST). Used under license CC BY-SA 3.0
Elaboration.
These dynamics of biological systems are extrapolated to human biology using the brain-gut microbiome interaction. Lactic Acid Bacteria (LAB) was chosen, because it is a beneficial bacteria found in humans’ gut; it helps to maintain a balanced gastrointestinal microbiota (gut flora). The next video shows the increased number of bacteria population of yogurt when a 20 billion of 11 different active cultures probiotic capsule (1) is added to the mix. Also note the milk protein clumps, which form an interesting scenery and texture. This was improved with the addition of the probiotic, because it contains fillers, e.g. starch, calcium salts, or sugars like lactose that show crystal formations under the microscope.
But what happens when the bacterial ecosystem is changed? External control can be exerted on its properties by electrolysis, where water molecules are broken apart, thus generating hydrogen and oxygen gases near the electrodes. This was done by driving 30 volts DC current to the microscope slide where the bacteria culture mix was being carefully examined. Furthermore, the voltage was triggered by an electroencephalography (EEG) module which was monitoring the electrical activity along the scalp as well as muscle movements of a subject. The sensitivity and signal used from the EEG’s electrodes was adjusted in order to use eye blinking to trigger the interaction.
EEG module with electrodes that monitor the electrical activity on the scalp and also muscle movements.
Voltage is triggered by blinking or by brainwave entrainment and sent to the microscope slide.
This is how an external depiction of the brain-gut microbiome was realized, and used as a metaphor for the Lotka-Volterra predator-prey system. The next video shows the variety of interactions achieved by experimenting with different voltages, switching polarity, and finding other areas where the environment was changing because of the the electrical manipulation. Note for example the change of direction and speed of bacteria, the rotation of the fillers, the sudden movements of the protein clumps, the formation of gas bubbles close to the electrodes, and, of particular importance, the dry areas where conditions for bacterial life decreased.
Why do humans engage in counterproductive behavior bringing grief upon themselves? We are predators of our own kind and as such, our species could be described by the Lotka-Volterra’s equations. O.D.E to Lotka Volterra is a visual representation of inner struggle, a human who is predator of him/her self, and thus preys on his own spirit. At some point he/she behaves in a self-destructive manner and at some other time he/she lives in harmony.
Discussion and further work.
At the current state of this work, very solid results were accomplished to convey the narrative by means of micromanipulation of bacteria. Further adjustments will be done in the three following areas:
- The EEG module: Only 2 electrodes were used in the frontal lobe to trigger the voltage. The subject could blink one eye at a time or both at the same time to get different results, e.g. different voltages. More electrodes can be used in other areas of the brain in orther to experiment with neurofeedback training at different neural oscillations (brainwave entrainment).
- The Bärtierchen board: The electronic board responsible to generate the voltage can also be finely tuned to better understand the gradient of voltages distributed across the microscope slide by the electrodes. Therefore, a higher level of control and aproximation to the Lotka-Volterra equations can be achieved on the bacteria.
- The bacteria culture: The behavior of the ecosystem also varies depending on the constitution of the mix. A thicker mix with more yogurt will behave differently than one with more water or probiotic. The design aesthetics of the bacteria environment relies largely on the proportions of these ingredients.
Furthermore, additional elements such as printed thin film may be added under the mix in order to use the gas bubbles as microlenses that could show interesting outcomes. Micro carving, painting and imprinting circuitry on the microscope slide are also techniques that could be used to improve the design and functionality of the ecosystem.
Programmed Cel Death (PCD), e.g autolysis by exposure to antibiotics, or ultraviolet germicidal irradiation (UVGI), short-wavelength ultraviolet (UV-C) light, can be integrated to increase the control of bacterial inactivation. UV lights can also improve the visual effects combining it with fluorescent liquid. A temperature of 71°C will also inactivate LAB. Pulsed Electric Field (PEF) Electroporation of bacteria is another approach to change the behavior of the baterial mix, although too complex to carry out at its current stage since it needs an electric potential difference in the order of 20 to 80 kilovolts per centimeter.
Water (H2O) electrolysis produces twice as much hydrogen (H2) gas at the cathode (-) than oxygen (O2) gas at the anode (+). This can be useful to control the mix, but brings the issue of partitioning the solution. Similarly, experimenting with other ionic compounds and changing the DC polarity would help to portray the Lotka-Volterra behaviour. Adding electrolytes to the mix such as salt (sodium chloride, NaCl), will contribute to visualize the ionization process.
Many more visual results were obtained in the video recordings. This material will be used with a myth-science sound piece to better portray the message and the background concept of this work. Sonification of the microinteraction will also be an integration to this project to create dynamic interactive psychoacoustic soundscapes. The myth-science sound piece project can be viewed in the following link:
(1) Contents of probiotic capsule: Bifidobacterium lactis, inulin, Lactococcus lactis, Lactobacillus plantarum, Lactobacillus acidophilus, Streptococcus thermophilus, Bifidobacterium longum, Lactobacillus rhamnosus, Lactobacillus bulgaricus, Bifidobacterium bifidum, Lactobacillus salivarius, Lactobacillus casei. Filler / Bulking agent: corn starch, modified starch / corn starch pregelatinized. Capsule Shell / Capsule shell: Hydroxypropylmethylcellulose, gellan. Release Agent / Anticaking agent: Magnesium stearate.
