Understanding How Our Brain Simulates Movement—And Why Some People Can't
Imagine you're about to pick up a coffee cup. Before your hand actually moves, your brain runs a kind of dress rehearsal, simulating the movement in advance. This mental simulation happens constantly, helping us plan actions, learn new skills, and even understand what other people are doing when we watch them move. But what happens when this internal movie projector breaks down?
That's the question neuroscientists in France set out to answer by studying a fascinating condition called aphantasia—the inability to generate visual mental imagery. While most research on aphantasia focuses on whether people can conjure up images in their minds, this study took a different approach. The researchers wondered: if people with aphantasia can't create mental images, does that also mean they can't mentally simulate movements?
To find out, they recruited 34 participants—half of whom had aphantasia and half who had typical visual imagery abilities. The researchers used a clever neuroscience technique involving transcranial magnetic stimulation (TMS), which uses magnetic pulses to safely stimulate specific brain regions. By measuring the electrical responses in participants' hand muscles when their motor cortex was stimulated, the scientists could detect whether the brain's movement-control system was actually "firing up" during mental simulations.
The experiment had two main parts. First, participants either imagined making a pinching motion with their thumb and index finger, or they watched videos of someone else making that same movement. In both cases, the researchers delivered TMS pulses to measure how active their motor system was. They also asked participants to complete questionnaires about how vivid their mental imagery felt and how often they used mental imagery in everyday life.
The results were striking. In people with typical imagery abilities, the researchers observed a clear increase in motor system activity during both tasks—imagining movements and watching others move. This makes sense: whether we're planning our own action or trying to understand someone else's movement, our brain simulates the motor sequence. But in people with aphantasia, something fundamentally different happened. Their motor system showed no increase in activity during either mental imagery or action observation, compared to resting baseline levels.
This wasn't just a case of people reporting that they couldn't visualize; it was a measurable, objective difference in brain function. The researchers had found neurophysiological evidence of real impairment, not simply a metacognitive problem—meaning aphantasia isn't just about what people think they can do, but reflects an actual difference in how their brains process motor information.
The implications are important for how we understand this condition. It suggests that aphantasia may involve a broader disruption in mental simulation than previously recognized, affecting not just visual imagery but the motor planning system itself. This distinction matters because it points toward genuine differences in neural function rather than mere self-reporting gaps or lack of effort. Some participants with aphantasia showed particularly limited abilities, though interestingly, the researchers found that certain individuals displayed complete impairment in one imagery type (like visual) while retaining some ability in another (like physical sensation).
The findings also carry practical significance. Understanding that aphantasia involves measurable motor system differences could eventually help clinicians develop better assessments and interventions. For people living with aphantasia, it provides scientific validation that their experiences reflect real neurological differences. And for the broader scientific community, it opens new questions about how mental simulation works and how disruptions in this system might affect learning, sports performance, rehabilitation after injury, or even social understanding.
What makes this research particularly elegant is how it moves beyond asking "can you imagine this?" to asking "what happens in your brain when you should be simulating?" By using objective neural measurements, the researchers have revealed that aphantasia isn't simply a deficit in conscious awareness or a quirk of reporting—it's a genuine difference in how the motor system engages during mental simulations, whether those simulations are explicit (deliberately imagining) or implicit (unconsciously activated by watching others move).