Biophysical characterization of the recording of unmyelinated and myelinated fiber activity with peripheral interfaces

Unmyelinated fibers account for a remarkable fraction of the peripheral nervous system and their activity is linked to many autonomic and somatic functions. While electrical recording of such activity from human-sized peripheral nerves holds significant potential for neuroengineering applications, it has been shown only in acute settings via microneurography. This leaves unclear whether current implantable electrodes could achieve the same outcome. To address this matter, we simulated recordings from the human vagus nerve through a transverse intrafascicular multichannel electrode (TIME), a microneurographic (μNG) needle, and a commercial cuff electrode. Recording signals were studied fiber-wise across relevant electrode insertions, revealing that the possibility of recording unmyelinated activity is shared by the TIME but unlikely by the cuff. These results suggest that no physical limitations of implantable electrodes underlie the missing evidence of recordings from unmyelinated fibers, and draw attention to experimental design choices that may have concealed this capability thus far.