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Explicit and implicit motor simulations are impaired in individuals with aphantasia

DOI: 10.1093/braincomms/fcae072
Dupont, W., Papaxanthis, C., Madden-Lombardi, C., & Lebon, F. (2024). Explicit and implicit motor simulations are impaired in individuals with aphantasia. Brain Communications, 6(2). doi:10.1093/braincomms/fcae072

Abstract

Individuals with aphantasia report having difficulties or an inability to generate visual images of objects or events. So far, there is no evidence showing that this condition also impacts the motor system and the generation of motor simulations. We probed the neurophysiological marker of aphantasia during explicit and implicit forms of motor simulation, i.e. motor imagery and action observation, respectively. We tested a group of individuals without any reported imagery deficits (phantasics) as well as a group of individuals self-reporting the inability to mentally simulate images or movements (aphantasics). We instructed the participants to explicitly imagine a maximal pinch movement in the visual and kinaesthetic modalities and to observe a video showing a pinch movement. By means of transcranial magnetic stimulation, we triggered motor-evoked potentials in the target right index finger. As expected, the amplitude of motor-evoked potentials, a marker of corticospinal excitability, increased for phantasics during kinaesthetic motor imagery and action observation relative to rest but not during visual motor imagery. Interestingly, the amplitude of motor-evoked potentials did not increase in any of the conditions for the group of aphantasics. This result provides neurophysiological evidence that individuals living with aphantasia have a real deficit in activating the motor system during motor simulations.

Authors

  • William Dupont1
  • Charalambos Papaxanthis1
  • Carol Madden-Lombardi1
  • Florent Lebon1

Understanding Aphantasia and Its Impact on Motor Simulations

Overview/Introduction

Aphantasia is a condition where individuals struggle or are unable to create mental images of objects or events. While it is known to affect visual imagery, its impact on the motor system and the ability to simulate movements mentally has been unclear. This study explores whether aphantasia affects motor simulations, which are crucial for understanding and predicting actions, through both explicit (motor imagery) and implicit (action observation) forms.

Methodology

The study involved two groups: individuals with normal imagery abilities (phantasics) and those self-reporting aphantasia (aphantasics). Participants were asked to imagine a pinch movement and observe a video of the same movement. Transcranial Magnetic Stimulation (TMS) was used to measure motor-evoked potentials (MEPs) in the right index finger, indicating corticospinal excitability, a marker of motor system activation.
  • Participants: 34 individuals, divided into phantasics and aphantasics.
  • Tasks: Imagining a pinch movement (visual and kinaesthetic) and observing a video of a pinch movement.
  • Measurement: TMS to trigger MEPs, assessing motor system activation.

Key Findings

  • Phantasics: Showed increased MEP amplitude during kinaesthetic motor imagery and action observation, indicating motor system activation.
  • Aphantasics: No increase in MEP amplitude in any condition, suggesting a deficit in motor system activation during motor simulations.
  • Self-Reports: Aphantasics reported difficulty in creating mental images, aligning with the neurophysiological data.

Implications

These findings provide neurophysiological evidence that aphantasia affects not only visual imagery but also the ability to engage the motor system during mental simulations. This has significant implications for understanding how aphantasia might impact everyday activities that rely on motor planning and learning, such as sports or rehabilitation exercises.
  • Practical Applications:
  • Motor Learning: Tailoring training methods for individuals with aphantasia.
  • Rehabilitation: Developing strategies that do not rely on motor imagery.
  • Education: Adjusting teaching methods to accommodate different imagery abilities.

Limitations

  • Sample Size and Selection: The study involved a self-selected group of aphantasics, which may not represent all individuals with the condition.
  • Gender Distribution: Unequal distribution of male and female participants, although no gender-specific effects were noted.
  • Motivation Assessment: The study did not assess participants' motivation, which could influence motor imagery and observation outcomes.
In conclusion, this research highlights the broader impact of aphantasia on motor simulations, offering insights into how this condition might affect various aspects of life and suggesting areas for further research and ...