Scientists have determined how our brains act differently when imagining movement than when we actually do it. It turned out that in both cases the previous signal occurred in the cerebral cortex, but in the case of imagined movements it was not clearly linked to a specific hemisphere.
The data obtained could potentially be used in medical practice to create neural trainers and control the recovery of neural networks in patients after stroke. The findings were published in the journal CerebralCortex.
Before we pick up a pen or put down a cup, the brain has formed a complete picture of the action. This visual-motor transformation ensures the accuracy of our movements. Understanding these mechanisms can help patients return to motor activities after stroke. But we don’t always finish the movement we start. In this case, visual information enters the motor areas of the cortex responsible for movement, but the onset of the reaction is blocked at a certain point, and the mental effort does not end with real muscle activation.
It's unclear how brain activity before an explicit action differs from brain activity before an imagined action. That's exactly what researchers decided to find out, because understanding our movements at the brain level will improve motor rehabilitation techniques after stroke.
Scientists from Skoltech and Moscow State University compared visual-motor transformations in real and imagined movements. To this end, the researchers conducted an experiment on 17 volunteers with an average age of 23 years old.
Subjects place their hands on a panel with two buttons that periodically light up, and participants only need to follow one of the two buttons. Once the button was lit, the actors had to press it, or imagine how they did it, depending on what the scientists wanted. During the experiment, the researchers recorded the volunteers' electroencephalograms. The neuroscientists then assessed signals in cortical areas associated with movement preparation and the emergence of hand sensations during movement.
During both imagined and real movements, the glow of the button elicited activity in the sensorimotor cortex, but only during real movements this activity was observed primarily in one hemisphere. The authors believe that before movement begins, a signal appears in the brain (the so-called presignal) that signals the conversion of visual stimulation into movement.
The results showed that the former signal was strongest in the fronto-central region of the hemisphere opposite the moving limb. That is, when a person presses a button with their right hand, the left hemisphere of the brain is activated, and vice versa. At the same time, if a person reacts slowly to the button's light and delays pressing the button, the duration of the previous signal increases.
The previous signals related to imaginary movement were not related to a specific hemisphere of the brain. Prior to movement, arousal accumulates in different areas of the sensorimotor cortex, suggesting differences in the way mental images are formed during imagined versus actual actions.
The authors also examined whether any signals appeared in the volunteers' brains when a button that the participants were not paying attention to was lit. The results showed that volunteers also had a prior signal when responding to non-target stimuli, although it was much weaker and shorter in duration than the target.
The presence of this non-target signal suggests that when the brain makes a decision, it first evaluates visual information and then makes the decision to block movement. At the same time, non-target signals also indicate that motor areas of the cortex do not remain inactive while the stimulus is being evaluated, and that the mere presence of a previous signal does not necessarily lead to an immediate motor response.
“Stroke disrupts the balance between inhibition and arousal in the cerebral cortex, as well as interactions between hemispheres and between the motor cortex and visual areas.
"We propose to use movement-related cortical signals to assess the state of the brain networks responsible for converting visual signals into actions in stroke patients. They can also be used to analyze the success of rehabilitation. This method will be highly sensitive, as it will allow recording improvements in the state of the brain's motor systems even before they manifest themselves in movement," says Nikolay Syrov, senior research scientist at Skoltech and one of the participants in the project.