Comment by Indemnity4 on 18/01/2024 at 02:55 UTC*

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View submission: Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology

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Signal to noise is really important plus unique quirk of human biology size (cleverly called biotic and abiotic factors).

The neuron is very small and the challenge is to capture a strong signal accurately and quickly. The neuron signal is about 100 microvolts.

The *impedance* between electrode-tissue interface decreases rapidly with increasing electrode size (big is best). You want the electrode as small as possible to be very selective about what it is signally (small is best). The signal amplitude is best when the electrode is large as you are only capturing local effects and reduce background noise (big is best). The whole device also has to fit in the limited space in the cavity (small is best).

Size, morphology (e.g. shape) and material choice are key options to control. It can be easier to use a small electrode and then use material tricks to make the surface area larger.

• Tethered* versus *untethered* electrodes are important too. The brain moves! Just from breathing and circulation. The larger and more rigid the electrode, the greater chance of unwanted cells forming a cavity. Brain infrastructure (meningeal fibroblasts) can form something like hard, lumpy scar tissue.

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