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- Hagberg, Elin Eriksson
(författare)
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Investigations of human cortical processing of gentle touch. A study with time-resolved electro-magnetic signal analysis
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present work summarizes investigations of the temporal correlates of brain activity elicited by gentle, moving touch on the hairy skin in healthy participants and in epilepsy patients. Light touch to the hairy skin activates two distinct afferent classes: fast conducting, Aβ afferents and slowly conducting C-tactile (CT) afferents. Aβ afferents signal discriminative aspects of touch, whereas CT afferents are proposed to play a role in affective touch. Using complementary neuroimaging methods with high temporal resolution, we aimed to distinguish between brain responses evoked by Aβ and CT afferents. In Papers I and IV, electroencephalography (EEG) showed that brush stroking on the hairy skin evoked an ultra-late potential, presumably driven by CT afference to the brain. Source localization indicated the cingulate cortex, and the precuneus as the underlying sources of this ultra-late potential. In Paper II, using magnetoencephalography (MEG) to spatially track brain activations in response to brush stroking over time, we showed that Aβ afference rapidly activates a well-defined network, including operculo-insular and cingulate regions. In Paper III, time- frequency analyses of MEG recordings from healthy participants were complemented with analyses of stereotactic EEG (SEEG) recordings from epilepsy patients. Here, we showed that naturalistic stroking touch induced spectral changes in alpha, beta, and gamma frequencies in sensorimotor regions and the posterior insula, similar to what has been described previously in studies using less naturalistic stimuli such as electrical median nerve stimulation. The present work contributes new information about the spatiotemporal evolution of the brain’s responses to caress-like touch and highlights the importance of considering both Aβ and CT afferents in gentle touch processing.
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| 2. |
- Hagberg, Elin Eriksson, et al.
(författare)
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Spatio-temporal profile of brain activity during gentle touch investigated with magnetoencephalography
- 2019
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Ingår i: NeuroImage. - : Elsevier BV. - 1053-8119 .- 1095-9572. ; 201
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Tidskriftsartikel (refereegranskat)abstract
- Positive affective touch plays a central role in social and inter-personal interactions. Low-threshold mechanoreceptive afferents, including slowly-conducting C-tactile (CT) afferents found in hairy skin, transmit such signals from gentle touch to the brain. Tactile signals are processed, in part, by the posterior insula, where it is the thought to be the primary target for CTs. We used magnetoencephalography (MEG) to assess brain activity evoked by gentle, naturalistic stroking touch on the arm delivered by a new MEG-compatible brush robot. We aimed to use high temporal resolution MEG to allow us to distinguish between brain responses from fast-conducting Aβ and slowly-conducting CT afferents. Brush strokes were delivered to the left upper arm and left forearm of 15 healthy participants. We hypothesized that late brain responses, due to slow CT afference, would appear with a time shift between the two different locations on the arm. Our results show that gentle touch rapidly activated somatosensory, motor, and cingulate regions within the first 100 ms of skin contact, which was driven by fast-conducting mechanoreceptive afference, and that these responses were sustained during touch. Peak latencies in the posterior insula were shifted as a function of stimulus location and temporally-separate posterior insula activations were induced by Aβ and CT afference that may modulate the emotional processing of gentle touch on hairy skin. We conclude that the detailed information regarding temporal and spatial brain activity from MEG provides new insights into the central processing of gentle, naturalistic touch, which is thought to underpin affective tactile interactions. © 2019 The Authors
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