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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

What This Study Is About

Researchers wanted to know if aphantasia—the inability to "see" things in your mind—also affects how the brain prepares for movement. They tested whether the brain’s "movement engine" revs up when a person either imagines moving or watches someone else move.

How They Studied It

The study looked at 28 people: 14 with aphantasia and 14 "phantasics" (people with typical mental imagery, or the ability to picture things in their mind).
Participants performed three tasks:
1. Visual Imagery: Trying to "see" themselves doing a pinch movement.
2. Kinaesthetic Imagery: Trying to "feel" the sensation of the pinch.
3. Action Observation: Watching a video of a hand pinching.
While they did this, researchers used TMS (a painless magnetic pulse to the head) to measure how "excited" the nerves controlling their fingers were. Think of it like checking if a car's engine is idling faster even if the car isn't moving yet.

What They Found

In people with typical imagery, the brain’s motor system "woke up" and got ready for action during the "feeling" and "watching" tasks. However, for those with aphantasia, the motor system stayed quiet. Their brains didn't show that typical spark of preparation. Essentially, while a typical brain "rehearses" a movement just by watching or feeling it mentally, the aphantasic brain didn't seem to engage in that same automatic rehearsal.

What This Might Mean

This suggests that aphantasia is more than just a lack of "mental pictures." It might be a broader difference in how the brain simulates *any* experience, including physical touch and movement.
However, we should be careful: this was a small study with only 28 participants, and they were "self-selected" (people who already knew they had aphantasia), which can sometimes bias results. It doesn't prove that people with aphantasia can't learn sports or dance; it just suggests their brains might use different "software" to get the job done!

One Interesting Detail

The researchers found that even when aphantasics were just watching a video of a hand moving, their motor systems didn't react. This means their brains process "seeing" an action differently than others, even when they aren't actively trying to imagine anything at all!
This summary was generated by AI and may contain errors. Always refer to the original paper for accuracy.