# Stimulation of single neurons at 7T: studies of the quantal components of touch

Roger Holmes Watkins, Ayan Sengupta, Rosa Sanchez Panchuelo, Paul M

Glover, Johan Wessberg, Susan T. Francis, Rochelle Ackerley

► To cite this version:

Roger Holmes Watkins, Ayan Sengupta, Rosa Sanchez Panchuelo, Paul M Glover, Johan Wessberg, et al. Stimulation of single neurons at 7T: studies of the quantal components of touch. 13th Scientific Day of the MRI-INT Centre, Oct 2022, Marseille, France. hal-05141591

HAL Id: hal-05141591

https://hal.science/hal-05141591v1

Submitted on 3 Jul 2025

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# Stimulation of single neurons at 7T: studies of the quantal components of touch

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Roger Watkins, Post-doc
LNC (UMR7291)
Roger.watkins@univ-amu.fr

Roger Watkinsª, Ayan Senguptaᵇ, Rosa Sanchez Pancheuloᵇ, Paul Gloverᵇ, Johan
Wessbergᶜ, Susan Francisᵇ, Rochelle Ackerleyª

a Aix Marseille Univ, CNRS, LNC (UMR 7291), Marseille, France
b Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, UK
c Department of Physiology, University of Gothenburg, Sweden

## Microneurography

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* Afferents identified & classified by responses to stroking/pressure/tapping/ blowing

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Intraneural implantation of tungsten microelectrodes allows us to record & characterize individual mechanoreceptive afferents in human subjects

### Intraneural microstimulation

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Receptive field
And sensation
Overlap precisely

<figure><img src="image_10.png" /></figure>

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* Shape

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* Borders

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* Movement

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* Free description

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Indentation

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SA-I
"focal pressure"

SA-II
"pressure /squeeze"

<figure><img src="image_18.png" /></figure>

INMS can be used to stimulate individual afferent neurons, and evokes distinctive sensations for each afferent type

## 7T fMRI

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Specialized equipment to allow intraneural microstimulation with neuroimaging

* Fully MEG/MRI compatible

* Optically isolated

* Soft switching between recording and stimulation allows long cables (prevents field induced currents and micro-shocks)

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7T Philips Achieva scanner
Head volume transmit coil and
32-channel receive coil

Intraneural recording
and stimulation

### Imaging sequence

gradient-echo, echo-planar imaging
sequence (TE = 25 ms, TR = 2 s,

### Protocols

#### Intraneural stimulation

8 x 60Hz trains (500ms on, 500ms off)

23s inter stimulus intervals

#### Vibrotactile stimulation

Amplitude and location matched 60Hz piezo actuator stimulation

### Analysis

fMRI data were analyzed using a general linear model (GLM) in FSL FEAT.

1.25mm voxels each fitted to canonical hemodynamic response function (HRF)

The fronto-parietal parietal network (FPN) and the default mode network (DMN) ROIs were obtained from Smith et al.

Bilateral hand area in S1 area ROI determined from the digit probabilistic atlas and thresholding

contrast masking to reveal group patterns of activations/deactivations between intraneural stimulation and vibration

## Results
### Global bold responses

Microstimulation (N = 14 single units)

<figure><img src="image_21.png" /></figure>

Amplitude & location matched vibration (N=14)

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Widespread Positive & negative BOLD responses induced by vibration and intraneural microstimulation

## Cortical network differences

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### Microstimulation

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### Microstimulation > vibration

Default mode network deactivation

### Vibration > Microstimulation

Ipsilateral S1 deactivation

## Conclusions

In addition to our previous studies of S1 activation

* strong global brain responses to single neuron activation

Comparison to matched vibration

* down-regulation of default mode network, reflecting salience of single neuron activation

* Lack of ipsilateral S1 inhibition when using INMS

* lack of parallel processing?

## Future steps

* Attentional control experiments, implicit task for subjects in microstimulation, not in vibration

* Mechanisms of the ipsilateral inhibition, attention or single neuron related?