Bioelectrics

Neurons are enclosed in semipermeable membranes. Protein pumps and channels direct electrochemical forces which move sodium, potassium, and chloride ions (with charges of +1, +1, and -1 respectively) through this membrane.

At rest, sodium-potassium pumps use energy to move sodium ions out and potassium ions in (at a ratio of 3 to 2) each against their concentration gradient creating a resting galvanic potential effected by ionic intracellular and extracellular concentrations.

When a neuron is triggered, sodium and potassium channels allow ion movement driven by electrical and concentration driving forces. Sodium channels open first, allowing sodium ions to flow in, then potassium channels open allowing potassium ions to flow out. Within a few milliseconds, the process ends and the neuron returns to its resting state.

This neural activation causes a minute spike in ion flux which contributes to triggering (or inhibiting) associated neurons and can be measured locally with sensitive electromagnetic field sensing instrumentation.

You can learn more about neurons in this teacher’s guide by the National Institute of Health. This video is good too 2-Minute Neuroscience: The Neuron.

Creating a Mind Machine Interface (MMI) requires, of course, connecting to a brain. This can be achieved directly or indirectly. Indirect methods involve external monitors such as those that track eye movements, breathing patterns, or other voluntary movement. Direct methods involve connection to bioelectric neural activity.

Electroencephalography (EEG) is often used to couple to the neural firing of the brain. With EEG, complex and sophisticated algorithms are required to differentiate between the myriad of signals. (EEG is explained in this great blog post by Bryn Farnsworth, Ph.D: What is EEG (Electroencephalography) and How Does it Work?) Making sense of the signals is further complicated by the dependency on an individual’s synaptic connection mapping which is more unique than fingerprints.

It is therefore desirable to provide connection to a brain’s neural firings while avoiding the dependency on individual brain formations. The obvious solution is to take advantage of the neural pathways in the peripheral nervous system which are independent of the brain’s synaptic connection mapping (as shown in this Biology Dictionary definition of the nervous system). By connecting to neural firings at the target neuromuscular junction, the control intent of the brain is easily differentiated.

Electromyography (EMG) involves coupling to the signals of cellular ionic flux on the surface of skin (surface EMG) with specially designed silver-chloride electrodes, or through the skin with subcutaneous electrodes that pierce the skin. These electrical signals are extremely small (measured in microvolts) and are buried in electrical noise several thousand times larger than the EMG signal.

You can learn more about EMG in this EMG article at Johns Hopkins or this blog post on EMG at SimpliFaster.

The design goals for EMG measurement are to produce meaningful signals optimally correlated to the true level of neural activity and ideally immune from environmental and superfluous interference.

Primarily required are: optimized bioelectric signal coupling to the target ionic flux, precision interfacing and amplification electronic circuitry, measurement noise reduction techniques, and advanced signal processing algorithms that extract, differentiate, and identify neural signaling signatures.

Optimizing these measurement technologies and techniques for useful applications is the focus of our research at Applied Neural Research Corp.