Scientists show that virtual reality illusions can physically cool down your real body

Visually tricking the brain into thinking a person’s left hand has crossed over to the right side of their body can physically cool down their actual, unmoving left hand. These findings suggest that disrupting the mind’s spatial map of the body can trigger measurable physiological changes in the physical limbs. The small study was published in the journal Cortex.

The human brain constantly builds and updates a model of the body by combining visual, tactile, and spatial information. This internal framework is known as the body matrix. The body matrix organizes sensory inputs into a cohesive map divided into a left and a right space. The invisible boundary separating these two halves is called the body midline.

When visual or physical information conflicts with this internal map, the brain actively tries to resolve the mismatch. In some cases of brain injury, this spatial mapping breaks down, causing patients to neglect one side of their body or feel disconnected from their own limbs. Healthy individuals can also experience temporary shifts in body perception through multisensory illusions.

Past experiments using fake rubber hands or mirrors have shown that tricking the brain into adopting an artificial limb can cause the real, hidden limb to drop in temperature. Researchers Matteo Girondini, Valentina Saccone, Massimo Montanaro, and Alberto Gallace wanted to test if they could induce similar physiological changes by disrupting the body’s midline boundary in a virtual environment.

The research team recruited twenty-six adults, all but one of them right-handed, for a sensorimotor experiment. The participants wore a virtual reality headset and held a controller in their right hand. Their real left hand rested comfortably on a table in front of them out of sight.

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Over a span of fifteen minutes, participants used their actual right hand to swing a virtual stick and push a virtual blue cube toward various targets. Every time the virtual stick collided with a cube, the controller in their right hand buzzed. This vibration provided synchronized physical and visual feedback to reinforce the illusion of interacting with the digital world.

Each participant completed the task twice on different days. In the congruent condition, the virtual hand holding the stick appeared as a standard right hand. In the incongruent condition, the virtual hand was visually replaced by a left hand. This created an illusion where the participant’s left hand appeared to be operating on the right side of their body space, perfectly mimicking the movements of their actual right hand.

The researchers tracked the temperature of the resting physical left hand using a non-contact thermal camera. They also monitored skin conductance, a measure of sweat gland activity that reflects changes in the nervous system. To trigger a skin conductance response, the researchers delivered mild, non-painful electrical stimulations to the back of the participant’s left hand midway through the virtual task.

Participants also completed a blindfolded pointing test before and after the virtual task. Without being able to see their hands, the participants used their right index finger to point to where they felt the fingers on their left hand were located. This allowed the researchers to measure proprioceptive drift, which is a shift in a person’s internal sense of their body’s physical location.

The researchers observed a drop in the skin temperature of the physical left hand during the incongruent condition. Tricking the brain into visualizing the left limb acting on the right side of the body space actively cooled the physical limb left behind on the table. By contrast, the temperature of the left hand increased during the congruent condition.

The overall frequency and intensity of the skin conductance responses did not differ between the two virtual setups. In the incongruent condition, the researchers found a positive correlation between temperature and skin conductance. Participants who experienced a larger drop in hand temperature also showed reduced skin conductance responses to the electrical stimulation. Warmer temperatures correlated with stronger nervous system responses.

The blindfolded pointing test revealed that participants felt their left middle finger had shifted slightly to the right after the training. This spatial drift occurred after both virtual conditions. The researchers suspect this happened because the participants were exclusively using and paying attention to the right side of their body during the entire exercise.

Subjective ratings of the virtual experience were similar across the board. Participants reported feeling an equal sense of control and embodiment over the virtual stick regardless of whether they were looking at a right or left virtual hand. The physiological cooling effect occurred without any conscious shift in how the participants perceived their bodies.

The study design includes a few limitations. The sample size was small, and the experiment only tested right-handed individuals using their dominant hand. The research team could not measure the temperature of the moving right hand during the task. This leaves it unknown whether the cooling effect is restricted to the stationary hand or if it extends to the actively engaged hand.

The current setup also makes it difficult to separate the effects of the visual illusion from the tactile vibrations. The physical feedback vibrating the right hand likely reinforced the bodily conflict, but its exact contribution to the temperature drop requires further testing.

Future research could explore whether applying magnetic or electrical stimulation to specific brain regions alters these temperature changes. This would help identify the exact neural circuits responsible for regulating body temperature during sensory conflicts.

Understanding how spatial perception affects bodily regulation could eventually inform virtual therapies for neurological conditions. For example, patients with complex regional pain syndrome often experience abnormal cooling in their affected limbs. Virtual reality exercises that manipulate the body’s midline boundary could offer a way to safely recalibrate these disturbed body maps and restore normal temperature regulation.

The study, “Shifting the body midline: The impact of visuomotor modulations in virtual reality on peripheral autonomic activity,” was authored by Matteo Girondini, Valentina Saccone, Massimo Montanaro, and Alberto Gallace.