In this webinar sponsored by ADInstruments, Professor Vaughan Macefield, one of the world’s leading neurophysiologists in the field of microneurography, speaks about the current trends in this field, and specifically shares methodology, tips and best-practices that he uses in his lab to answer complex questions about physiological processes and associated stimuli. Key topics covered during this webinar included… - What is Microneurography and what sort of scientific questions can it answer? - What are the current trends in the field? - What equipment is needed to do this type of work? - Tips, tricks and best-practices for the Microneurography technique - Important data acquisition and analysis processes Background: While many neurophysiologists use invasive techniques to record from the brain or peripheral nerves in anaesthesed animals, such approaches have – of necessity – been rather limited in human subjects. However, 50 years ago the first direct recordings of nerve activity from peripheral nerves in awake human subjects were published. In Uppsala, Sweden, Karl–Erik Hagbarth and Åke Vallbo developed the technique of “microneurography”, in which an insulated tungsten microelectrode is inserted through the skin and into a muscle or cutaneous fascicle of a peripheral (or cranial) nerve. Their original aim was to understand the population behavior of muscle spindles during voluntary contractions, but they soon discovered that they could record from individual myelinated sensory axons supplying muscle or skin. Moreover, they confirmed that the same microelectrodes could record spontaneous and evoked activity generated by the unmyelinated sympathetic axons.

1. Professor Vaughan Macefield presents microneurography
techniques and research trends for the study of nerve
stimuli and associated responses in human subjects.
Microneurography:
Recording Nerve Traffic Via Intraneural
Microelectrodes in Awake Human Subjects

2. Microneurography:
Recording Nerve Traffic Via Intraneural
Microelectrodes in Awake Human Subjects
Vaughan G. Macefield, PhD
Professor of Physiology
Mohammed Bin Rashid University of Medicine & Health Sciences, Dubai, UAE
Professor of Integrative Physiology
School of Medicine, University of Western Sydney
Conjoint Senior Principal Research Fellow
Neuroscience Research Australia, Sydney

3. MICROELECTRODE RECORDINGS FROM PERIPHERAL NERVES IN
AWAKE HUMAN SUBJECTS
Microneurography – developed by Karl-Erik Hagbarth and Åke Vallbo in
Uppsala, Sweden, in the mid ‘60s - has contributed significant information
on tactile and proprioceptive sensation, pain, sensorimotor control and
control of the sympathetic nervous system
Tungsten microelectrodes can be inserted into any accessible peripheral
nerve – such as the median or ulnar nerves at the wrist or upper arm, the
peroneal or tibial nerves at the knee, or the sural nerve at the ankle.
Microelectrodes can also be inserted into branches of cranial nerves, such
as the inferior alveolar or supraorbital branches of the trigeminal nerve.

4. The Neuro Amp EX is a low-noise and high-gain isolated differential
amplifier suitable for all recording environments requiring a wide
bandpass (100 Hz to 5 kHz) and a high signal-to-noise ratio

5. The Neuro Amp EX isolated headstage provides a gain of 100 X with a 10 Hz
High Pass filter. The cable shielding is directly connected to the casing, limiting
the need for additional shielding at the input terminals. It is certified safe for
direct human connection, making it ideal for microneurography

6. To learn more about ADInstruments
solutions for microneurography, go here >>

7. Tungsten microelectrode inserted into the common peroneal nerve in an awake
human subject, via the NeuroAmpEX headstage

8. ECG
2 s
via tungsten microelectrodes inserted
percutaneously into common peroneal nerve
microneurographic recording from
muscle spindle afferents and
muscle sympathetic postganglionic
axons in awake human subjects
integrated nerve
m10 V
instantaneous frequency
0
20
Hz
muscle
fascicle
sponteously active muscle
spindle primary ending
muscle sympathetic
(vasoconstrictor)
bursts

9. Spontaneous bursts of muscle sympathetic nerve activity (MSNA) using the NeuroAmp EX amplifier
noisep-p8 V
noiserms1.7 V

10. Single-unit recording from a human Golgi Tendon Organ ending in tibialis
anterior during voluntary dorsiflexion of the ankle
action potentials recorded from
common peroneal nerve
firing rate during contraction
dorsiflexion force
TA EMG
target force

11. Single-unit recording from a fast-adapting type I cutaneous afferent to forces
applied to the finger pad

12. Single-unit recording from a slowly-adapting type II cutaneous afferent to forces
applied to the finger pad

13. Multi-unit recording of spontaneous bursts of muscle sympathetic nerve activity
covarying with blood pressure and heart rate
increase in
heart rate
increase in muscle
vasoconstrictor drive

14. Spike Histogram software can be used to extract the negative-going spikes of muscle
sympathetic nerve activity, and the positive peaks of the ECG and respiration

15. Cross-correlation and auto-correlation histograms can be constructed to examine the
influence of respiration and the cardiac cycle on muscle sympathetic nerve activity

16. It can also be used to examine the effects of Galvanic Vestibular Stimulation (GVS) on the timing of
sympathetic spikes, extracted here from a recording that included a muscle spindle afferent

17. Sinusoidal galvanic
vestibular stimulation
causes a frequency-
dependent modulation
of sympathetic outflow
to muscle and skin

18. We can also make single-unit recordings from individual postganglionic
sympathetic axons supplying muscle and skin

19. We can characterise
the firing properties
of individual, type-
identified,
postganglionic
sympathetic neurones
in health and disease

20. This is also seen in pathophysiological states of high muscle vasoconstrictor
drive, such as obstructive sleep apnoea, hypertension and heart failure

21. Because the NeuroAmpEX headstage is made from high-grade stainless
steel it is intrinsically MR-compatible; using the NeuroAmpEX we can
record from peripheral nerves while scanning the brain.
We have been correlating bursts of muscle sympathetic nerve activity
(MSNA) and skin sympathetic nerve activity (SSNA) with brain activity in
healthy subjects, as well as in patients with obstructive sleep apnoea.
MSNA-coupled fMRI and SSNA-coupled fMRI allows us to identify
regions of the brain that are temporally coupled to the bursts of MSNA
or SSNA and hence are involved in generating sympathetic nerve
activity.

23. MSNA recorded from peroneal nerve via tungsten microelectrodes in 3T scanner
+300 Hz high-pass digital filter
reduced background noise
improved signal:noise

24. measurement of individual sympathetic bursts
MSNA recorded from peroneal nerve via tungsten microelectrodes in 3T scanner

25. Muscle sympathetic nerve activity (MSNA) burst amplitude is measured every 1 s during the 4 s
inter-scan period. BOLD fMRI signal intensity is measured 4 s later during the 4 s scanning period to
account for neurovascular and nerve conduction delays
4 s block4 s inter-scan
period
BOLD
4 s scanning
period
MSNA

26. significant coupling between spontaneous MSNA and increases in BOLD signal intensity
was found in several cortical and subcortical areas (n=15)

27. significant coupling between spontaneous MSNA and increases in BOLD signal intensity
was found in several cortical and subcortical areas (n=15)

28. Vaughan G. Macefield, PhD
Thank You:
www.adinstruments.com
vaughan.macefield@mbru.ac.ae
For additional information on the products and applications presented
during this webinar please visit www.adinstruments.com