summary: Researchers have investigated how mechanical memory of previous fingertip forces influences the activity of tactile neurons.
This study revealed the importance of the viscoelasticity of the fingertip, which causes deformation to last longer than the applied force and influences the information sent to the brain. This indicates that our brain receives data of current forces as well as “memories” of previous forces.
This discovery opens the door to understanding hand control and tactile-based behavior in everyday tasks.
Important facts:
- The viscoelastic nature of the fingertip means that force-induced deformation lasts longer than the actual force, affecting the information conveyed to the brain by tactile neurons.
- The researchers observed the neural responses of different types of neurons (FA-1, SA-1, and SA-2) to different forces using a robot that mimics interactions with natural objects.
- The study discovered diverse responses of tactile neurons, suggesting that tactile neurons relay rich information about the viscoelastic state of the fingertip and retain a “memory” of past interactions.
sauce: e-life
The scientists detailed how the activity of tactile neurons in the fingertip in response to applied force is influenced by the fingertip’s mechanical memory of previous forces.
This research today e-life In the reviewed preprint, the editors present fundamental discoveries about how fingertip viscoelasticity (a time-dependent mechanical response to applied force) affects the information conveyed to the brain by tactile neurons. We offer what we call.
This finding highlights that these neurons signal the fingertip viscoelastic memory of the current fingertip force and previous loads. Tactile information about the recent physical state of the skin may help the brain formulate precise motor commands to control the hand in object manipulation and tactile tasks.
The everyday tasks we perform with our hands, such as cooking, cleaning, grasping and carrying objects, require us to repeatedly apply force to external objects accurately and quickly.
To accomplish these tasks effectively, the brain relies on information provided by tactile neurons about the forces acting on the fingertips. However, these neurons do not directly transmit contact forces. Rather, it conveys information about the deformation caused in the skin by the applied force.
“The viscoelasticity of the human fingertip means that the deformation caused by a force acting on the fingertip lasts longer than the force itself,” said lead author Hannes Saar, senior lecturer in psychology at the University of Sheffield, UK. I will explain.
“Residual deformations from previous forces therefore influence how the fingertip responds mechanically when subjected to new forces. However, this physical memory may not be present during natural hand use. The extent to which it affects tactile neuron signaling is not well understood.”
To investigate this, Saal and colleagues examined how previous fingertip forces affected the responses of primary tactile neurons when a new force was applied. They used a custom-made robot to stimulate fingertips with forces that mimic those typically encountered during interaction with natural objects.
They recorded the impulse responses of about 200 individual neurons using specially designed electrodes inserted into the volunteers’ peripheral nerves. Neurons were classified into fast adaptation type 1 (FA-1), slow adaptation type 1 (SA-1), and slow adaptation type 2 (SA-2).
Forces were applied successively to the fingertip in different directions. By comparing fingertip deformations and evoked neural responses in stimulus sequences in which the directional order of the stimuli was held constant and in sequences in which the order was systematically varied, the research team found that the previous force stimulus The effects of stimuli on responses were analyzed.
First, we noticed that the deformation of the fingertip changed more significantly when the load history was changed, supporting the viscoelastic memory of the fingertip. Next, we investigated whether this increased variability in deformation was reflected in neuronal responses.
They found that, compared to when the directional order was fixed, the firing rate during force application varied approximately twice as much in FA-1 and SA-1 neurons, and by approximately 70% in SA-2 neurons. We found that there was significant variation.
This indicates that fingertip viscoelastic memory influences the response of tactile neurons. The difference in effect sizes between neuron types may be due to the fact that type 1 neurons primarily sense mechanical events in superficial structures of the skin, whereas type 2 neurons primarily sense tension states in deep tissues. There may be.
The researchers then investigated whether increased variability in neuronal responses was associated with fingertip viscoelastic memory. To achieve this goal, the researchers quantified the information conveyed to the brain about the current and previous direction of force.
They found that information about the direction of the current force is reduced when the previous stimulus varies systematically compared to when the previous stimulus is consistent. Interestingly, we also observed considerable diversity in the behavior of individual neurons within each type. Some neurons primarily convey information about the current direction of the force, while others convey both the current and previous direction, and some neurons primarily convey the previous direction.
Furthermore, we discovered that many SA-2 neurons are active even in the absence of external stimulation and can transmit information about the viscoelastic deformation state of the fingertip even while the fingertip is under load.
This diversity of responses suggests that primary tactile neurons collectively convey rich information to the brain about the viscoelastic state of the fingertip, including memories of past stimuli.
Co-author Ingvars Barzniks, Associate Professor at the University of New South Wales, Sydney, said: A more accurate interpretation of type 1 neuron inputs may be possible. ”
The authors note that there has been no systematic investigation into whether the effects of viscoelasticity on tactile sensing affect performance in manual tasks, so whether viscoelasticity may limit performance or They point out that it remains unclear whether neural information about past stimuli is used by the brain in any action. capacity.
Additionally, this study could benefit from more directly examining the link between skin deformation and neuron firing, as suggested in the eLife public review, in which the authors I’m currently working on it.
“Our findings suggest that a population of tactile neurons continuously provides information to the brain about the viscoelastic deformation state of the fingertip,” said Dr. Author Professor Roland Johansson concludes:
“We believe that the brain uses this information to estimate the state of the fingertip during the planning and evaluation of tactile actions. Future research could explore this idea with interesting possibilities. Masu.”
About this tactile memory research news
author: emily packer
sauce: e-life
contact: Emily Packer – eLife
image: Image credited to Neuroscience News
Original research: Open access.
“Manipulating memory at your fingertips: How viscoelasticity affects tactile neuron signaling” by Hannes Sah et al. e-life
abstract
Manipulating memory at your fingertips: How viscoelasticity affects tactile neuron signaling
Human skin and underlying tissues constitute a viscoelastic medium, meaning that deformation depends not only on the currently applied force but also on the recent loading history. The extent to which this physical memory influences primary tactile neuron signaling during natural hand use is not well understood.
Here, we present the historical response of fast-adapting (FA-1) and slow-adapting (SA-1 and SA-2) primary tactile neurons innervating the human fingertip to loads applied in different representative directions. We investigated the influence of the load on the Description of the object manipulation task.
We found that variations in the preceding load affect the overall signaling of neurons regarding the direction of the force. Some neurons continue to signal the current direction, while others continue to signal both the current direction and the previous direction, or primarily the previous direction.
Furthermore, the ongoing impulse activity of SA-2 neurons during loading conveyed information related to the viscoelastic deformation state of the fingertip during loading.
We conclude that population-level tactile neurons signal continuous information about the viscoelastic deformation state of the fingertip, shaped by both recent history and current loading.
Such information may be sufficient for the brain to correctly interpret the current force load and calculate precise motor commands for manipulation and interaction with objects in tactile tasks.