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Study is about understanding role of somatosensory learning.

Active vs Passive movement = robot vs moving arm by self in this context

tried to show off their new robot (!) meaning a more methodological paper than theoretical

Aim: Motor skill acquisition involves integrating sensory feedback to refine movements, highlighting the somatosensory system's crucial role.

Hypotheses:

Learning via passive movements with reinforcement is as effective as through active movements.

The somatosensory system is pivotal in the early stages of motor skill acquisition, challenging the focus on motor output.

Participants - 230, mean age 21, all RH, no sensory motor disorders. a further 36 recruited for the visual part of the experiment

Method -

Participants: Performed reaching movements toward an unseen target using a robotic arm.

Design: Differentiated between active (participant-generated) and passive (robot-generated) movements, with and without reinforcement (success signal).

manipulation effect of passive vs active movement

comparison of effect of binary feedback over reinforcement

active reinforcement, passive reinforcement, active and passive control

Design - experimental, within subjects design

IV - 3 conditions above

DV - movement error

Major findings - Both active and passive movements with reinforcement improved motor accuracy and somatosensory perceptual acuity, retained over a week.

Strengths:

Innovative approach to dissect motor learning components prev studies have not established that somatosensory perception is crucial here

Methodologically sound, with clear definitions and controlled conditions.

Limitations:

Limited generalisability due to the specific task and use of robotic arm hard to apply to real life, they tried to justify this by saying it was close to real life

why is reinforcement important was not really covered in introduction

Did not justify sample size

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This study was investigating healthy adults learn a continuous implicit motor task when the Primary Somatosensory Cortex (S1) is altered using rTMS.

Authors hypothesised that the magnitude of change associated with motor learning would differ between experimental and sham groups.

Theory

Sensory feedback is thought to play an important role in learning new motor skills. Previous research relied on animals and stroke as a model - problematic due to array of lesion presentations, as well as difficulty identifying the contributions of motor, sensory and cognitive systems.

Participants

Twenty-seven right-handed participants (13 females; mean age 25.7 years [range 19–48]) with no reported neurological deficits or sensorimotor impairment

Design

Experimental, mixed design overall - Participants were randomly assigned to one of 2 groups. Either rTMS or sham

Spread over 6 days.

Experiment 1 - sought to evaluate the impact of 1 Hz rTMS applied over S1 on somatosensation

Experiment 2 - sought to assess the impact of 1 Hz rTMS applied over S1 on motor learning.

Considered long-term impact after 2 weeks using retention tests.

Method

1 experiment really, not 2!

Experiment 1 – Neurostimulation technique – experiment 1 assessed whether the rTMS numbed the participants or not.

Experiment 2 – Follow up test, tracking performance.

Results

Cutaneous somatosensation, was decreased in the Experimental group compared to the Sham group.

This persisted even in the absence of the rTMS.

Participants improved performance across the delayed retention test so there was still a main effect of sequence found even after the two week follow up.

None of the groups gained explicit knowledge of the repeating sequence.

There was an effect of time.

rTMS showed the effect of cutting out the S1 region which reduced the learning of motor skills.

Conclusion

Disruption of somatosensation impairs the degree of change associated with motor learning.

Discussion

Addresses concerns of previous research

Artificiality of the task

Doesn’t really show learning – rather prevention of learning over time

Not necessarily clear in certain areas

Participants of this study were young healthy adults - limits generalization

Size of rTMS effect was variable between participants.

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Introduction:

The experiment was conducted as there was an advancement in methodology (rTMS)

Using TMS, they can advance invasive animal studies with correlational stroke studies and introduce a new technique.

The study is a mixed design as participants took part in both experiments; however, as there were randomised sham trials, it was not a within-participants design.

1. IV - 1Hz or sham.

DV- calculation of RMSE

2Time

Hypothesis:

In Experiment 1, the researchers hypothesised that 1 Hz repetitive transcranial magnetic stimulation (rTMS) over the primary somatosensory cortex (S1) would impair contralateral cutaneous somatosensation and proprioception in healthy participants. Subsequently, in Experiment 2, the hypothesis was that disrupted somatosensation, induced by 1 Hz rTMS over S1, would impact implicit motor-skill learning of a continuous sequence. The researchers expected that the magnitude of change associated with motor learning would differ between the experimental and sham groups, indicating the importance of accurate somatosensation feedback in motor learning.

The study investigates how altering somatosensation affects motor learning in healthy adults.

They use repetitive transcranial magnetic stimulation (rTMS) to alter somatosensation in the brain's primary somatosensory cortex (S1).

In the first part of the study:

rTMS disrupted participants' ability to feel touch on their wrists/hands.

Effects on wrist movement sensation varied among participants.

In the second part of the study:

Participants practised a motor task while receiving either real or fake rTMS.

Those who received real rTMS showed less improvement in the motor task than those who received fake rTMS.

Effects on motor learning persisted even after rTMS was stopped.

Experiment 1 Findings:

Somatosensory Function:

Cutaneous somatosensation decreased in the Experimental group compared to the Sham group.

There was a trend for decreased proprioceptive ability in the Experimental group.

Follow-up Testing:

Changes in cutaneous somatosensation and proprioception did not persist two weeks after stimulation.

Experiment 2 Findings:

Acquisition Practice:

Reductions in tracking error were more significant for the Sham than for the experimental group during repeated and random sequence practice.

( up to 6 days later) Retention:

Both groups demonstrated sequence-specific motor learning at the retention test.

The Experimental group continued to make more tracking errors even when rTMS was not delivered.

(2 weeks later) Follow-up Testing:

Sequence-specific motor learning persisted for both groups two weeks after the original retention test.

The difference in tracking errors between the groups was no longer present at the follow-up test.

Explicit Knowledge:

Neither group gained explicit knowledge of the repeating sequence.

Discussion Points:

rTMS Effects on Sensation:

1 Hz rTMS to S1 transiently impaired cutaneous somatosensation but not proprioception.

Motor Skill Learning:

The Experimental group showed persistently higher tracking errors, suggesting impaired motor learning with altered somatosensation feedback.

Findings resemble motor behaviour observed in individuals with stroke-related brain damage, indicating the importance of accurate sensory processing for motor learning.

Conclusions:

Somatosensation is crucial for learning new motor skills in healthy adults.

Even mild to moderate sensory impairment can negatively impact motor learning.

Sensation, such as stroke, should be considered in motor rehabilitation after central sensory loss.

These findings emphasise the importance of intact somatosensation for motor learning and have implications for learning theory and rehabilitation medicine.

The study suggests that altering somatosensation during task practice impairs motor learning, possibly affecting the development of an accurate internal movement model.

Limitations

Smirnov doesn't show a normal distribution.

Further research is needed on the impact of other TMS stimulation types

Tms may not effectively replicate a lesion.

Ecological validity: The lab test is not transferrable to more naturalistic activities. The participants were young and healthy, so we are not sure what the effects would be.

Self-reported measures may be biased.

Causality—S1 is connected to many other areas of the brain, so it is not definitive that S1 is responsible for that function. However, it does show that S1 is involved in a process.

Other imaging techniques could have been used to strengthen the causality.

Strengths

It filled a void—the first use of the wrist and the first assessment of the effect of 1Hz rTMS on proprioception.

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Bernardi et al  - Somatosensory Contribution to the Initial Stages of Human Motor Learning

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Bernardi et al  - Somatosensory Contribution to the Initial Stages of Human Motor Learning

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Introduction:

A theoretical-based study.

Experimental model to investigate the relative contribution of motor and sensory factors to human motor learning.

The researchers were aiming to introduce a novel methodology.

Methods:

Mixed Methods design

IV- 1)Type of movement 2) reinforcement vs not reinforcement 3) time -pre and post.

DV- Movement accuracy

·       230 participants (mean age 21.9 ± 2.1 years),

·       all right-handed with

·       no history of sensorimotor disorders,

·       The study's experimental setup required participants to reach for an unseen target within a bar without seeing their arm, investigating the effects of active versus passive movement and the impact of binary feedback (reinforcement) on movement success.

Within subject factor - Time

Between subject factors:

1) active reinforcement,

2)passive reinforcement,

(active control, and passive control),

·       Participants were divided into four groups:

1) active reinforcement,

2)passive reinforcement,

(active control, and passive control), with specific subgroups performing reaching movements either straight ahead or at a 135° orientation to evaluate the generality across movement directions. A separate group was also included for a visual control experiment.

The methodology involved using a two degree-of-freedom planar robotic arm for reaching movements, with visual feedback mechanisms designed to guide movement accuracy and duration without direct vision of the arm. The experiment began with baseline movements without feedback, followed by training procedures tailored to each group, focusing on reinforcing accurate reaching movements with visual cues and binary feedback for success, with modifications based on the experiment's orientation (straight-ahead or 135°) and the nature of movement (active or passive).

The study meticulously controlled for movement direction, feedback, and training conditions to explore the nuances of motor learning and sensory feedback's role in refining motor skills.

Training Duration and Structure: Training consisted of 150 trials for tasks performed straight-ahead and 200 trials for tasks performed at a 135° angle, based on pilot findings indicating the latter required more practice for reliable learning. Breaks were administered halfway through the straight-ahead condition and every 50 trials in the 135° condition.

Active Reinforcement Condition: Participants actively performed reaching movements. Successful movements within a specified target range triggered a visual reward. The training aimed to examine the effect of active participation and reinforcement on learning the task.

Passive Reinforcement Condition: Participants experienced the same movements generated by the robot, based on trajectories from active participants, without actively controlling the movement. They received the same rewards for successful movements to investigate the impact of passive experience and reinforcement on learning.

Control Conditions (x2): Both active and passive control groups performed similar movements without receiving feedback rewards. The active control group aimed to refine their movement precision through repetition without external success indicators, while the passive control group experienced movements generated by others without rewards. These controls were designed to assess learning effects absent reinforcement feedback.

Compliance and Attention Checks: Participants in passive conditions were instructed to focus on the sensation of the movements and report specific occurrences (rewards or slow movements), ensuring engagement. Compliance with not exerting force on the robotic handle during passive movements was monitored.

Participants were tested in blocks of 100 trials with various trajectories, and motor performance was quantified by measuring deviation from a straight path to a target.

The study also assessed the force applied by subjects during passive movements to ensure that active force production was minimal, supporting the focus on passive learning mechanisms.

Analysis of learning effects was conducted by comparing pre-training and post-training performance, using statistical methods to evaluate changes in motor performance and perceptual classification accuracy. The study found no significant differences based on the experiment version (straight-ahead vs. 135° trajectories), indicating consistent learning effects across conditions.

Learning stability over time and the influence of different types of reinforcement (visual vs. none) were also examined, revealing insights into how individuals adapt their motor performance and sensory perception through training. The results contribute to understanding the somatosensory basis of early motor learning, highlighting the role of passive movements and the potential for sensory feedback to enhance motor skills development.

Results:

Passive training paired with reinforcement produces motor learning

Some participants received feedback in the form of an on-screen explosion when their movements ended within a specific range near the target, while others received no feedback.

The key findings include:

1.    Improvement with Reinforcement: Both active and passive participants who received reinforcement showed significant reductions in movement error towards the target, compared to those who did not receive any feedback.

2.    Enhanced Somatosensory Perception: Participants who received reinforcement also demonstrated improvements in somatosensory classification accuracy following training, an effect not observed in control groups without reinforcement.

3.    Motor Learning Across Conditions: Data analysis revealed that active participants with reinforcement managed to reduce their movement error significantly, indicating successful motor learning. This was evidenced by a progressive increase in reinforced trials over training.

4.    Passive Training Effectiveness: Even participants in passive conditions, when paired with reinforcement, showed improvement, highlighting that passive training can produce motor learning similar to active engagement.

5.    Statistical Analysis: A repeated-measures ANOVA confirmed that participants who received reinforcement exhibited significant reductions in errors from pre-training to post-training, unlike those without reinforcement. This was consistent across multiple-measures of movement.

Evaluation

Descriptive Statistics -

Limitation - the lack of information about the recruitment of the participants. How could we generalize the findings regarding the population?

Very little information was provided regarding the participants or the researcher's approach to recruitment.

·         Could have provided the gender ratio

·         Could have provided the eligibility criteria and recruitment procedure

·         The mean age of 21.9 years was provided but no age range given

·         Medical history was given (all right-handed and no history of sensorimotor disorders)

How can we generalize the findings if we are not given data about the participants?

Also regarding the age data given, if it was just for younger participants is this a population bias – if you test early motor skills would the results not be better with just the younger age range.

Low ecological validity because the experiment was artificial. This is not how we learn motor functions.

Strength - the methodology section was very detailed and showed the reader the intended novel approach they were proposing

in depth statistical analysis

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Experimental design:

The study consisted of two main experiments spread over six days. The participants were randomly assigned into two groups: one received 1 Hz rTMS(repetitive Transcranial Magnetic Stimulation) over the primary somatosensory cortex (S1), and the other received sham rTMS, mimicking the conditions of actual rTMSwithout the neurological effects. The experiments aimed to assess the impact of rTMS on somatosensation and motor learning.

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The study suggests that somatosensation plays an important role in motor learning, and even mild to moderate sensory impairment can negatively impact motor learning. 

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The study suggests that somatosensation plays an important role in motor learning, and even mild to moderate sensory impairment can negatively impact motor learning. 

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The study extends previous work by demonstrating the impact of somatosensation on motor learning, highlighting the importance of developing novel rehabilitation approaches to enhance recovery of sensory loss after stroke

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The study extends previous work by demonstrating the impact of somatosensation on motor learning, highlighting the importance of developing novel rehabilitation approaches to enhance recovery of sensory loss after stroke

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Studies were either based on invasive experiments on the brains of animals, or by studying people who have acquired brain injuries. This study is novel because it is the first of its kind to design experiments on healthy individuals learning a new motor task when somatosensation is altered by rTMS.

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n = 17 Participants were all healthy volunteers with no neurological deficits

DV + participants ability to track cursor on screen.

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result: mild to moderate sensory impairment can negatively impact motor learning.

Sensation is an important part of rehabilitation after central sensory loss, such as a stroke.

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Results for experiment 1

1. Somatosensory Function:

• Cutaneous Somatosensation: There was a significant decrease in two-point discrimination ability in the Experimental group compared to the Sham group, indicating that rTMS over S1 disrupted cutaneous somatosensation in the wrist/hand.

• Proprioception: The impact of 1 Hz rTMS on wrist proprioception, tested by limb-position matching (LPM), was variable, showing a trend but not a statistically significant difference between groups.

2. Follow-up Testing :

• Both groups returned to their pre-TMS baseline for cutaneous somatosensation and proprioception, suggesting that the effects of rTMS on these sensory functions were temporary.

Results for Experiment 2:

1. Acquisition Practice:

• During practice, both groups improved their performance in the continuous wrist tracking task. However, the Experimental group showed less improvement compared to the Sham group, indicated by higher tracking errors and smaller performance improvements.

2. Retention:

• At the no-rTMS retention test, both groups showed improved tracking performance from practice, but the Experimental group continued to perform worse than the Sham group. This suggests that disrupting somatosensation with rTMS over S1 impairs the quality of motor learning.

3. Follow-up Testing (2 weeks post rTMS):

• Differences in tracking performance between the Experimental and Sham groups were no longer observed, indicating that the long-term impact of altered sensation during practice did not persist.

4. Explicit Knowledge:

• There was no evidence that participants gained explicit knowledge of the tracking task, as both groups did not recognize the repeating sequence better than chance.

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Limitation: Is S1 area of brain the only area of the brain responsible for learning?

Are the tasks appropriate? is tracking a cursor a suitable motor task?

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Bernardi et al. (2015)

Methods

230 right handed participants with no recorded history of sensorimotor disorders.

Experimental setup, random assignment to four conditions.

Two manipulations: reaching to a bar without seeing it either by themselves or with help of a robotic arm.

Participants would get either positive feedback of reaching the target or no information.

Time was checked as a factor (pre-training vs. post-training assessments).

Mixed design: 2x between subject and 1 within participants design.

Results

Passive and active learning with reinforcement showed comparable improvements.

Reinforcement contributed to higher performance during the task.

Passive movements with reinforcement led to long-term retention of learning.

Binary reinforcement paired with somatosensory stimulation was crucial for retention.

Evaluation

Strengths:

The use of the robotic arm is novel.

More than one version of the experiment was performed to mitigate for different directions of movements.

Retention testing.

Robust explanation of the methods.

Limitations:

Unclear: the extent to which somatosensory and motor system dominate learning in early motor skill acquisition.

Limited data on demographics.

Lack of novelty of the findings (reinforcement).

Only behavioural and judgement tasks, no neurological tests (e.g. EEG).