Last updated: 2020-06-16
Requirements
The requirements necessary for replacement neurons involve the following high-level elements.
Input
Status: Semi-viable
Organic Model: the dendrites of a neuron receive output from other neurons through synaptic connections with those neurons’ axons. The reception of that output is made possible by neurotransmitters that occupy the synaptic space between axon and dendrite.
Engineered Models: highly-sensitive conductive material can already be used to receive delicate electrical signals from a given source. However, there are no currently available methodologies to obtain neurotransmitter concentration measurements in real time, let alone from a specific synapse.
Processing
Status: Viable
Organic Model: a neuron emits signals if the electrical potential within the neuron is greater than the resistance needed to convey that current to the synapse at the end of its dendrites. This is controlled by an electrochemical process within and surrounding the neural cell. Further, the availability of neurotransmitters in a synapse are what conveys the signal from one particular axon to a particular dendrite on another neuron. In this way, synaptic neurotransmitters can act as a rate limiter between neurons. Together, the firing of a neuron and the ability to transmit that signal to another neuron are the basic mechanisms that constitute neural processing.
Engineered Models: computation of an input signal’s strength versus a threshold, and tracking the frequency of signal propagation, are both simple problems for hardware or software to handle. A simple capacitor, while crude, does this by its very nature. Highly sensitive and delicate electronics can be manufactured today for low cost to handle these mechanisms. Software is also an efficient way to handle these mechanisms.
Output
Status: Semi-viable
Organic Model: the axon of a neuron conveys the output when it fires to the synaptic connection(s) between the axon and another neuron’s dendrite. If adequate neurotransmitters are available within a given synapse, the signal will be conveyed to the dendrite on the other side of the synapse. If not, the signal will not be conveyed across that particular synapse.
Engineered Models: as the determination of whether to send a signal to another neuron can be performed at the processing level in an engineered model, engineering neurotransmitters at the output stage isn’t necessarily required. Therefore, passive conductive material is all that is needed to convey the electrical output of an engineered device to its intended recipient(s).
Available Devices
Passive Conductors
It is relatively simple to detect the emission of faint electrical signals by way of direct connectivity with conductive material. The issue mostly lies in the scale – being able to target an individual axon. Advances in nano-material fabrication may be one solution to this problem.
Smart Conductors
If the issue with passive conductors could be resolved, it would not be too difficult with current technology to add some manner of signal processing to that mechanism. This processing could be done with either basic electronics such as resistors, capacitors, and so forth, or with software. Both could be used to determine whether an output signal should be emitted based on the total quantity of input signal received. The most limiting factor however at this time remains getting the signal input into the device, and therefore passive conductors that are small and durable enough are necessary for smart conductors to be truly viable in a practical application.
