A team of mathematicians and neurobiologists from the Weizmann Institute of Science to give them an answer to the question of how our brain encodes the complex movements required for writing. Their findings were recently published in the scientific journal Neuron.
The muscles required to move the hand in writing on a sheet of paper are different from those used to write large letters on a blackboard, yet the shape of the letters, with their twists unique to each person, is similar in both cases. How does our brain encode the complex movements required for writing? Does he use one set of instructions - both for writing on paper and for writing on a board, or are they different sets? These questions have been debated among neurobiologists for some time. Now a team of mathematicians and neurobiologists from the Weizmann Institute of Science managed to give them an answer. Their findings were recently published in the scientific journal Neuron.
One of the team of scientists is research student Naama Kadmon Harpaz, whose work combines mathematics with neurobiology. She did her master's degree in the department of neurobiology at the Weizmann Institute of Science, and is currently doing her third degree in the laboratory of Prof. Tamar Flesh, in the department of computer science and applied mathematics. Neurobiologist Dr. Ilan Dinstein, formerly a post-doctoral researcher in Prof. Rafi Malach's laboratory, and currently a faculty member at Ben Gurion University of the Negev, also participated in the study.
For the purpose of the study, Kadmon Harpaz, Dr. Dinstein and Prof. Flesh asked volunteers to write three letters - both in large and small letters, on a touch screen, when they cannot see what they wrote. While writing, their brains were scanned using an MRI machine, in order to identify the activity The brain that underlies the physical action. In addition, the team members analyzed the writing movements: both their geometric properties and their duration, as well as their kinematics (that is, the speed of the movement and its direction).
Above: tracking the writing movement of uppercase (in blue) and lowercase (in orange) letters of three subjects. Below: The calculation of the average movement of the two sizes shows an analogy at each scale of movement
With the accumulation of the results and their analysis, unequivocal findings emerged: certain areas of the brain encode both the writing of capital letters and that of small letters in a similar way. In mathematical terms it can be said that the coding in these areas "does not depend on the scale"; That is, the brain activity pattern is very similar on every scale - big or small, fast or slow. This finding, a "uniform code for all", is in line with previous studies, which implied that despite the use of different muscles, the kinematic basis of writing lowercase and uppercase letters is the same.
The results of the fMRI scan revealed two brain regions involved in this encoding. One is the anterior intraparietal sulcus, an area in the parietal lobe that is recognized as a central factor in actions that require hand-eye coordination and movement planning. The second area is the primary motor area (M1), and it is considered the executor of the hand movement. In the hierarchy of the brain, the aIPS is considered "higher" than M1, meaning it processes more abstract information. Therefore, it may be possible to estimate that it is this area that encodes movements regardless of their size. However, the scientists were surprised to discover that the "lower" area, M1, which is always considered the immediate source of nerve commands sent to the spinal cord and from there to the muscles, and is involved in more mechanical aspects of movement, is also responsible for coding movements that do not depend on scale.
The scientists believe that the lack of dependence on the size of the movement or similar variables is intended to facilitate the control of the movement, and to increase the processing efficiency of the neural information. Prof. Flesh says: "When it comes to creating movement, the assumption is that the brain works 'top down' - from abstract representations to physical actions However, we discovered abstract coding in areas that are considered relatively low. We believe that the motor areas of the brain work more as a network, and less as a rigid and clear hierarchy. In addition, it seems that abstract patterns are used to encode motor actions performed on the world around us."
This experiment is one of the first to use fMRI scanning to study movement control in humans. Most studies using fMRI examine the brain's response to inputs - such as images or videos, while studies examining output - such as movement, are usually done using electrodes that measure the activity of many or single neurons in primates, but not in humans. "By using fMRI to examine movement control in humans," says Dr. Dinstein, "we were able to see many areas of the brain at once. We could also see how each of them works in relation to the other."
Prof. Flesh believes that these findings may be relevant for a large number of research fields. For example, the insight that emerged from them regarding the way the brain works may be applied in the field of robotics and bio-robotics, to improve the efficiency of movement and enable a wide range of complex movement. In addition, it may help to understand movement disorders that originate in the brain, such as Parkinson's disease and paralysis due to cerebral hemorrhage. It may also lead to a better understanding of the "motor memory" that we use every day, unconsciously. To this end, additional questions must be answered, including: At what stage of learning to write is writing that does not depend on scale become possible? And how does this type of motor learning occur in the brain?
