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Using Facial Electromyography to Assess Facial Muscle Reactions to Experienced and Observed Affective Touch in Humans
Published on: March 15, 2019
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Autistic traits modulate cortical responses to affective but not discriminative touch
Connor J Haggarty1, Peter Malinowski1, Francis P McGlone1,2
1Research Centre for Brain & Behaviour, School of Natural Sciences & Psychology, Liverpool John Moores University, Liverpool, UK.
The European Journal of Neuroscience
|December 4, 2019
Summary
This study reveals distinct neural pathways for fast, discriminative touch (A-beta fibers) and slow, affective touch (C-tactile afferents). The ultra-late potential (ULP) linked to affective touch showed reduced amplitude in individuals with autistic traits.
Area of Science:
- Neuroscience
- Somatosensation
- Psychophysiology
Background:
- The sense of touch is traditionally viewed as discriminative, involving fast-conducting A-beta (Aβ) afferents for object interaction.
- A distinct system involving slow-conducting, unmyelinated C-tactile afferents (CTs) is proposed to process the affective qualities of touch.
- CT afferents exhibit unique velocity tuning, responding optimally to stimuli moving at 1–10 cm/s, unlike the linear response of Aβs.
Purpose of the Study:
- To compare the temporal dynamics of neural responses to fast (Aβ-targeted) and slow (CT-targeted) touch using event-related potentials (ERPs).
- To investigate the functional significance of CT afferent activation, particularly its relationship with affective touch perception and autistic traits.
Main Methods:
- Utilized event-related potentials (ERPs) to measure brain activity in response to controlled stroking stimuli applied to the skin.
- Differentiated neural responses based on stimulus velocity to target either fast (Aβ) or slow (CT) somatosensory pathways.
- Correlated the amplitude of specific ERP components (P300, ultra-late potential) with self-reported levels of autistic traits.
Main Results:
- A higher amplitude P300 component was observed for fast (Aβ-targeted) touch compared to slow (CT-targeted) touch.
- A previously identified C-fibre specific ultra-late potential (ULP) was associated with CT-targeted input.
- The amplitude of the ULP showed a negative correlation with self-reported autistic traits, suggesting a link to affective processing.
Conclusions:
- Findings support the existence of separate discriminative and affective touch systems within the somatosensory pathways.
- The ultra-late potential (ULP) serves as a neural marker for CT afferent activation and affective touch processing.
- EEG temporal resolution offers a valuable tool for exploring individual differences in sensitivity to affective touch, particularly in relation to autistic traits.
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