Differential effects of hypnotizability on visuomotor adaptation and sequential motor learning

The human body is a master of adjustment. When you reach for a cup of coffee, your brain does not simply fire a command to your arm; it constantly predicts where your hand will go and compares that prediction with what your eyes and muscles actually feel. If the cup is moved unexpectedly, your brain instantly recalibrates the movement to correct the error. This process, known as sensorimotor adaptation, relies heavily on a small, wrinkled structure at the back of the brain called the cerebellum. In parallel, the brain learns complex sequences of actions, like typing or playing a musical instrument, through a different set of circuits that connect the outer surface of the brain with deep structures involved in habit formation. While these two learning systems work together in daily life, they are distinct. Scientists have long wondered if individual differences in how our brains are wired might affect one system more than the other. One such difference is a trait called hypnotizability. This is not about being controlled by a stage performer, but rather a stable, natural variation in how a person's mind and body respond to suggestions. Some people are highly responsive, while others are less so. Research has already shown that highly hypnotizable people have subtle differences in the size and shape of their cerebellum, which might explain why they sometimes struggle with balance or precise aiming when their visual input is altered.

A team of researchers at the University of Pisa and the Université Claude Bernard Lyon 1 set out to see if this trait creates a split personality in motor learning. They wanted to know if people who are highly hypnotizable would struggle with the quick, error-correction style of adaptation while still being able to learn slow, repetitive sequences just as well as everyone else. To find out, they recruited thirty-three healthy adults and first measured their hypnotizability using a standard scale that involves following a series of simple suggestions, such as imagining a hand is stuck to a table or that a smell is unpleasant. Based on their scores, the researchers divided the participants into two groups: a medium-to-high hypnotizable group and a low-to-medium group. The study took place in a quiet, dimly lit room to ensure that external distractions did not interfere with the measurements.

The first test was a visuomotor adaptation task. Participants sat in front of a computer screen and used a joystick with their non-dominant hand to move a cursor toward a target. In the beginning, the cursor moved exactly as the joystick moved. Then, the researchers introduced a twist: they rotated the visual feedback. When a participant moved the joystick to the right, the cursor on the screen appeared to move twenty degrees to the left, or vice versa. The participants were instructed to move their hand to hit the target as accurately and quickly as possible, which required them to learn to compensate for the visual rotation. They performed hundreds of these reaches, and the researchers tracked how many times they hit the target and how straight their path was. The results showed that both groups eventually learned to compensate for the rotation and hit the target at similar rates. However, a closer look at the path their hands took revealed a difference. The highly hypnotizable participants made larger, more erratic deviations from a straight line, particularly when the visual feedback was rotated to the right. They could hit the target, but their journey there was less precise. Throughout this task, the researchers also monitored the participants' heart rate and skin conductance, which are indicators of the body's stress or alertness levels. They found that as the participants practiced, their bodies showed a pattern of increasing alertness followed by a return to calm, suggesting that the brain was actively working to master the new rules, regardless of hypnotizability.

Next, the participants switched to a sequential motor learning task. This time, they used their non-dominant hand to tap a specific eight-finger pattern on a keyboard as quickly and accurately as possible. They repeated this sequence for ten blocks of thirty seconds each. Unlike the previous task, there were no visual tricks or rotations here; the goal was simply to get faster and more accurate at the same repeating pattern. In this scenario, the highly hypnotizable group performed just as accurately as the low-hypnotizable group. They both learned the sequence and improved their speed over time. The only difference was that the highly hypnotizable participants moved slightly slower overall. Their heart rates and skin conductance remained steady and did not change much between the two groups, indicating that this type of repetitive learning did not trigger the same physiological shifts seen in the adaptation task.

The study concludes that hypnotizability does not make a person generally bad at learning motor skills. Instead, it affects specific types of learning in different ways. The highly hypnotizable individuals showed a reduced ability to fine-tune their movements when sensory feedback was distorted, a task that relies on the cerebellum. This aligns with previous findings that their cerebellum has slightly different physical characteristics. However, when it came to learning a repetitive sequence, which depends more on the connections between the outer brain and deep brain structures, they performed just as well as everyone else, even if they were a bit slower. The researchers suggest that these differences are not due to a lack of effort or attention, but rather reflect how the brain naturally processes motor commands and sensory information. The findings reinforce the idea that the brain is not a single, uniform machine, but a collection of specialized systems that can be influenced by deep-seated psychological traits. By understanding how these traits shape our ability to adapt and learn, scientists can better map the complex relationship between the mind, the body, and the environment.