Microneurography and Intraneural Microstimulation for Upper Limb Sensory Investigation in Healthy and Amputee Subjects

Official title

Experimental Study to Investigate Sensory Control of the Upper Limb Through Microneurography and to Restore Near-natural Tactile Sensations Through Intraneural Microstimulation in Healthy and Amputee Subjects

Overview

The goal of this experimental study is to investigate the somatosensory system through intraneural recording and stimulation of the median nerve in healthy volunteers and participants with upper-limb amputation. The main questions it aims to answer are: * How does median nerve activity encode tactile perception during different types of mechanical tactile stimulation in healthy subjects? * How can tactile information be artificially encoded and restored through intraneural microstimulation in both healthy subjects and upper-limb amputee participants? How rich and functionally meaningful is the restored sensory information? * What are the neurophysiological mechanisms underlying tactile stimulus processing and the associated patterns of brain activation during tactile stimulation? Participants will undergo median nerve recordings using microneurography during controlled mechanical tactile stimulation, as well as intraneural microstimulation with specific patterns to evoke near-natural tactile sensations. They will perform perceptual reporting tasks related to stimulus type, intensity, and localization, as well as psychophysical tests under different stimulation conditions. When possible, they will also undergo non-invasive recordings of brain activity using electroencephalography during sensory stimulation.

Detailed description

Participants will attend the laboratory where the entire research protocol will be conducted in a single visit lasting up to 4 hours.

Medical history and a physical examination will be collected. In participants with amputation, additional clinical information from previous neurological assessments will be reviewed (including medical records, nerve conduction velocity data, and ultrasound or MRI examinations required to verify inclusion/exclusion criteria). Psychometric tests will also be administered to assess language abilities, visuospatial skills, and general intelligence, ensuring that participants are able to understand and perform the experimental tasks. If inclusion and exclusion criteria are met, participants will undergo microneurography and/or intraneural microstimulation procedures. Participants will be seated comfortably, with the dominant arm (healthy volunteers) or the residual limb (participants with amputation) supported. A trained medical operator will identify the median nerve using external stimulation and/or ultrasound guidance to assist electrode insertion. The active electrode will be inserted into the nerve, while a reference electrode will be placed in the subcutaneous tissue a few centimeters away. Correct electrode placement will then be refined using intraneural stimulation. Once the nerve fascicle is reached, tactile stimulation of the hand will be used to identify single mechanoreceptive units. Final electrode placement will be confirmed by visual and auditory inspection of the neural signal. The median nerve activity must be clearly distinguishable from background activity when mechanical stimuli are applied to the skin. During electrode insertion, participants will be instructed to remain still until the procedure is completed. The intraneural microstimulation session, performed in both healthy volunteers and participants with upper-limb amputation, is preceded by peripheral neural recordings using microneurography during the presentation of tactile stimuli (e.g., Von Frey filaments). This step is used for accurate nerve localization and preliminary assessment of the receptors and their receptive fields. Once the neural target is identified, participants undergo intraneural stimulation involving the perception and recognition of artificially generated tactile stimuli. These stimuli are delivered via intraneural microstimulation and are derived from mechanoneural transduction, using a sensorized artificial finger interacting with different surfaces to encode surface-dependent tactile information. Participants will be asked to recognize different properties of the presented stimuli. During the tests, electroencephalographic (EEG) activity may be recorded using a 128-channel EEG system, synchronized with the onset of stimulation.

Interventions

• Procedure Microneurography
  Microneurography is a minimally invasive neurophysiological technique that allows direct recording of the electrical activity of single peripheral nerve fibers using specific microelectrodes inserted into the nerve.
• Procedure Intraneural Microstimulation
  Intraneural microstimulation is a minimally invasive neurophysiological technique in which small electrical currents are delivered through a microelectrode inserted into a peripheral nerve to selectively activate nerve fibers and evoke sensory perceptions.

Primary outcome measures

• Mechanoreceptor identification success rate [Time frame: During the experimental protocol (up to 3 hours)]
• Mechanoreceptor classification accuracy [Time frame: During the experimental session (up to 3 hours)]
• Peripheral afferent firing rate during tactile stimulation [Time frame: During the experimental session (up to 3 hours)]
• Tactile mechanical detection threshold [Time frame: During the experimental session (up to 3 hours)]
• Receptive field size of mechanoreceptive afferents [Time frame: During the experimental session (up to 3 hours)]
• Perceived sensory perception during intraneural microstimulation [Time frame: During the experimental protocol (up to 3 hours)]
• Perceived intensity of tactile sensations elicited during intraneural microstimulation [Time frame: During the experimental protocol (up to 3 hours)]
• Perceived location of tactile sensations elicited during intraneural microstimulation [Time frame: During the experimental protocol (up to 3 hours)]
• Tactile discrimination performance [Time frame: During the experimental session (up to 3 hours)]

Secondary outcome measures (4)

• Event-related potential amplitude during intraneural microstimulation [Time frame: During the experimental protocol (up to 3 hours)]
• Event-related potential latency during intraneural microstimulation [Time frame: During the experimental protocol (up to 3 hours)]
• EEG spectral power modulation during intraneural microstimulation [Time frame: During the experimental session (up to 3 hours)]
• Decoding accuracy of tactile stimulation conditions from EEG signals [Time frame: During the experimental session (up to 3 hours)]

Eligibility criteria

Inclusion criteria

Healthy participants

• Age between 18-60 years, of any sex
• Signed informed consent
• No neurological diseases
• Presence of both intact upper limbs
• Normal language, visuospatial, and general intellectual abilities, assessed using the Wechsler Adult Intelligence Scale-Revised (WAIS-R) (Appendix 1)

Amputee participants

• Age between 18-60 years, of any sex
• Signed informed consent
• Upper-limb amputation (transradial or hand amputation)
• Stable amputation for at least one year
• Normal language, visuospatial, and general intellectual abilities, assessed using the Wechsler Adult Intelligence Scale-Revised (WAIS-R) (Appendix 1)
• Evidence of residual peripheral nerve function in the stump, based on nerve conduction studies as documented in clinical records

Exclusion criteria

Healthy participants

• Conditions affecting perceptual abilities
• Inability to provide informed consent
• Pregnancy or breastfeeding (self-reported)
• Clinical conditions that, in the judgment of the investigator responsible for recruitment, may interfere with microneurography, microstimulation, and EEG procedures
• Current or past substance abuse
• Brain injury with residual motor impairment
• Depression
• Presence of neurological or musculoskeletal disorders
• Diabetes mellitus
• Current or previous dermatological conditions
• Morphological nerve abnormalities, as indicated by ultrasound or MRI findings in clinical records
• Upper-limb amputation

Amputee participants

• Psychological and/or cognitive disorders
• Inability to provide informed consent
• Pregnancy or breastfeeding (self-reported)
• Clinical conditions that, in the judgment of the investigator responsible for recruitment, may interfere with microneurography, microstimulation, and EEG procedures
• Current or past substance abuse
• Brain injury with residual motor impairment
• Depression
• Presence of neurological or musculoskeletal disorders
• Diabetes mellitus
• Current or previous dermatological conditions
• Morphological nerve abnormalities, as indicated by ultrasound or MRI findings in clinical records
• Bilateral upper-limb amputation

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Open label

Primary purpose

Basic science

Study locations

Italy · 1 center

• Laboratorio Congiunto di Microneurografia e Microneurostimolazione — Pisa

Publications

• Ackerley R, Watkins RH. Microneurography as a tool to study the function of individual C-fiber afferents in humans: responses from nociceptors, thermoreceptors, and mechanoreceptors. J Neurophysiol. 2018 Dec 1;120(6):2834-2846. doi: 10.1152/jn.00109.2018. Epub 2018 Sep 26. PMID 30256737
• Oddo CM, Raspopovic S, Artoni F, Mazzoni A, Spigler G, Petrini F, Giambattistelli F, Vecchio F, Miraglia F, Zollo L, Di Pino G, Camboni D, Carrozza MC, Guglielmelli E, Rossini PM, Faraguna U, Micera S. Intraneural stimulation elicits discrimination of textural features by artificial fingertip in intact and amputee humans. Elife. 2016 Mar 8;5:e09148. doi: 10.7554/eLife.09148. PMID 26952132
• Vallbo AB. Microneurography: how it started and how it works. J Neurophysiol. 2018 Sep 1;120(3):1415-1427. doi: 10.1152/jn.00933.2017. Epub 2018 Jun 20. PMID 29924706
• Statache M, Filosa M, Ballanti S, D'Alesio G, Di Salvo G, Camboni D, Oddo CM. Neuromorphic Touch Sensors for Pleasantness Encoding via Spike Patterns: A Bio-Inspired Artifical Fingertip for Restoring Affective Sensations. IEEE Sensors, 2024, Kobe, Japan. doi: 10.1109/SENSORS60989.2024.10784624.

Identifiers

NCT: NCT07691957 · 18385_TADDEI · TUNEBEAM_MICROAMP

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗