Our behavior is largely related to the way we control, organize and perform the movements in the right order. Take the writing, for example. If we did not make one line after another on a page, we could not write a word.
However, motor skills (simple or linked actions that, in practice, do not require any effort) can become very difficult to learn and recover when neurological conditions interfere with planning and control of sequential movements. When a person is suffering from a disorder, such as dyspraxia or stuttering, some skills can not be performed in a harmonious and coordinated manner.
Traditionally, scientists believed that in a sequence of actions, each of them was closely associated with each other in the brain and that one triggers the next. But if this is correct, how can we explain the sequencing errors? Why do we type "form" instead of "de", for example
Some researchers argue that before starting a sequence of actions, the brain recalls and plans all the elements at the same time. It prepares a map where each element has an activation buffer with respect to its order in the sequence. These compete with each other until the element with the strongest activation wins. It "goes out" for execution as being more "prepared" – so we type "f" in the word "de" first, for example – and then it is erased from the map. This process, called competitive queuing, is repeated for the rest of the actions until all the elements of the sequence are executed in the correct order.
A 2002 study showed that the brain uses simultaneous activity activations before any movement. While the monkeys were drawing shapes (for example, three lines for a triangle), the researchers discovered that before the beginning of the movement, there were simultaneous neuronal patterns for each trait. The strength of the activation could predict the position of this particular action in the run.
Planning and waiting line
Until now, it was not known if this activation system was used in the human brain. We also do not know how the actions are queued as we prepare them based on their position in the sequence. However, recent research by neuroscientists at Bangor University and University College London has shown that there is also simultaneous planning and competitive queuing in the brain human.
As part of this study, researchers were interested in seeing how the brain was preparing to execute well-learned action sequences, such as typing or playing the piano. Participants were trained for two days to combine abstract shapes with five-finger sequences in a computer task. They learned the sequences by watching a small dot move from one finger to the other on an image of the hand displayed on the screen and pressing the corresponding finger on a response device. These sequences were combinations of orders of two fingers with two different rhythms.
On the third day, the participants had to produce – on the basis of the abstract form presented for a moment on the screen – the correct sequence entirely of memory while their brain activity was recorded.
By examining the cerebral signals, the team was able to distinguish neural patterns from the participants during the planning and execution of the movements. The researchers found that a few milliseconds before the start of the movement, all finger pressures were queued and "stacked" in an orderly fashion. The pattern of finger pressure activation reflected their position in the sequence immediately afterwards. This model of competitive queuing showed that the brain was preparing the sequence by organizing the individual actions in the right order.
The researchers also investigated whether this preparatory waiting line activity was shared between different sequences with different rhythms or different finger sequences, and found that this was the case. The competitive queuing mechanism served as a model to guide each action in a position and provided the basis for the accurate production of new sequences. In this way, the brain remains flexible and efficient enough to be ready to produce combinations of unknown sequences by organizing them with the help of this preparatory model.
Interestingly, the quality of the preparatory scheme predicted the accuracy with which a participant produced a sequence. In other words, the more activities or actions were well separated before the execution of the sequence, the more likely the participant was to execute the sequence without error. The presence of errors, on the other hand, meant that waiting for reasons in preparation for action was less well defined and tended to mix.
By knowing how our actions are pre-planned in the brain, researchers will be able to know the parameters of executing sequences of fluid and precise movements. This could lead to a better understanding of the difficulties encountered in learning disorders and sequence control, such as stuttering and dyspraxia. It could also help in the development of new techniques of rehabilitation or treatment that optimizes movement planning so that patients can more effectively control the sequences of action.