Summary: Researchers have discovered the area in the brain where stiffness perception is formed.
Every day, people use their hands effortlessly to assess an object’s stiffness, like the ripeness of a piece of fruit. For the first time an international team of scientists led by UCL, have discovered the area in the brain where stiffness perception is formed. The findings, published in the Journal of Neuroscience, could aid rehabilitation in patients with sensory impairments.
Hands do not have sensors to directly inform the brain about an object’s stiffness. To uncover the link between our brain and our hands, researchers focused their attention on how motion and sensory inputs are combined and processed. The team looked to the posterior parietal cortex (PPC); a key part of the brain which plays an important role in planning movements, spatial reasoning and attention. Could the PPC also be involved in stiffness perception?
Lead researcher Dr Marco Davare (UCL Institute of Neurology) said: “There is already evidence that a position controller exists in this brain area, however it is still unknown whether this area also combines force and position information – a prerequisite for us to sense stiffness.”
Sensory signals such as position and force travel back to the brain and are combined with a copy of motor commands to adjust movement and provide us with a sense of the environment.
Dr Davare said: “For some actions, we clearly rely on one of these signals more than the other. For example we rely on position feedback when reaching for a pen, but on force feedback when putting pressure on the nib to write.”
To test their theory, researchers from UCL and Ben-Gurion University of the Negev (Israel) set up a virtual reality environment whereby participants were asked to probe different virtual force fields using a robotic stylus and report which one was stiffer.
The team attempted several experiments with transcranial magnetic stimulation over the PPC and another area of the brain involved in motor control known as the dorsal premotor cortex. The results showed that subjects made errors in sensing stiffness when the PPC was stimulated – but not the dorsal premotor cortex.
Virtual reality games reveal the sense of stiffness.
The study, funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the Royal Society, sheds light on brain mechanisms essential to the interaction between our movements and their effect on sensory perception.
Dr Davare, UCL said: “The hand is a frontier between the brain and our surrounding environment: how I move my hand has a consequence on what my hand can feel. Our findings could have considerable impact on the development of virtual reality systems and could help to inform treatments to improve quality of life for patients with sensory impairments.”
About this neuroscience research article
Funding: Funding provided by Biotechnology and Biological Sciences Research Council (BBSRC) and the Royal Society.
Source: Harry Dayantis – UCL Image Source: NeuroscienceNews.com image is credited BBSRC. Video Source: The video is credited to BBSRC. Original Research: Full open access research for “Stimulation of PPC Affects the Mapping between Motion and Force Signals for Stiffness Perception But Not Motion Control” by Raz Leib, Firas Mawase, Amir Karniel, Opher Donchin, John Rothwell, Ilana Nisky, and Marco Davaren in Journal of Neuroscience. Published online October 12 2016 doi:10.1523/JNEUROSCI.1178-16.2016
Cite This NeuroscienceNews.com Article
[cbtabs][cbtab title=”MLA”]UCL. “How We Sense Stiffness.” NeuroscienceNews. NeuroscienceNews, 13 October 2016. <https://neurosciencenews.com/neuroscience-stiffness-5288/>.[/cbtab][cbtab title=”APA”]UCL. (2016, October 13). How We Sense Stiffness. NeuroscienceNews. Retrieved October 13, 2016 from https://neurosciencenews.com/neuroscience-stiffness-5288/[/cbtab][cbtab title=”Chicago”]UCL. “How We Sense Stiffness.” https://neurosciencenews.com/neuroscience-stiffness-5288/ (accessed October 13, 2016).[/cbtab][/cbtabs]
Stimulation of PPC Affects the Mapping between Motion and Force Signals for Stiffness Perception But Not Motion Control
How motion and sensory inputs are combined to assess an object’s stiffness is still unknown. Here, we provide evidence for the existence of a stiffness estimator in the human posterior parietal cortex (PPC). We showed previously that delaying force feedback with respect to motion when interacting with an object caused participants to underestimate its stiffness. We found that applying theta-burst transcranial magnetic stimulation (TMS) over the PPC, but not the dorsal premotor cortex, enhances this effect without affecting movement control. We explain this enhancement as an additional lag in force signals. This is the first causal evidence that the PPC is not only involved in motion control, but also has an important role in perception that is disassociated from action. We provide a computational model suggesting that the PPC integrates position and force signals for perception of stiffness and that TMS alters the synchronization between the two signals causing lasting consequences on perceptual behavior. SIGNIFICANCE STATEMENT When selecting an object such as a ripe fruit or sofa, we need to assess the object’s stiffness. Because we lack dedicated stiffness sensors, we rely on an as yet unknown mechanism that generates stiffness percepts by combining position and force signals. Here, we found that the posterior parietal cortex (PPC) contributes to combining position and force signals for stiffness estimation. This finding challenges the classical view about the role of the PPC in regulating position signals only for motion control because we highlight a key role of the PPC in perception that is disassociated from action. Altogether this sheds light on brain mechanisms underlying the interaction between action and perception and may help in the development of better teleoperation systems and rehabilitation of patients with sensory impairments.
“Stimulation of PPC Affects the Mapping between Motion and Force Signals for Stiffness Perception But Not Motion Control” by Raz Leib, Firas Mawase, Amir Karniel, Opher Donchin, John Rothwell, Ilana Nisky, and Marco Davaren in Journal of Neuroscience. Published online October 12 2016 doi:10.1523/JNEUROSCI.1178-16.2016