#neuroprothetics

Picturesource Polina Tankilevitch Pexels

A measure for movement

A team of neuroscientists at the German Primate Center (DPZ) - Leibniz Institute for Primate Research in Göttingen have investigated how the goal of an arm movement is spatially encoded in the primate brain. Their findings are relevant for the development of neuroprostheses, among other things, as it is essential for their control that the information read from the brain is interpreted in the correct spatial reference system. The work has been published in Nature Communications. The aim of neuroprosthetics is to replace or restore the loss of functions in the human nervous system as far as possible using the smallest technological systems. Neuroprostheses are used by means of microsystems technology and biocompatible materials for the multiple contacting of nerves and control of implantable assistance systems. The control of neuroprosthetics, i.e. the connection between the brain and the nervous system, is becoming more finely structured with increasing technologization, right up to the use of algorithms. The implementation of spatial understanding from the brain requires corresponding applications that can be transferred to the prosthesis via the nervous system. A kind of replacement for the motor end plate is required!

The peripheral nervous system (PNS), which works in interaction with the central nervous system (CNS), has its sensory organs in every part of the body. It receives sensory information and transmits it to the CNS via sensory fibers. Movement impulses originating from the CNS are transmitted to the target organs such as muscles, tendons and ligaments via motor fibers of the PNS. Both the CNS and the PNS are neuronally connected to the brain via the spinal cord. It has been known for some time that the target of an arm movement is coded in some brain regions relative to our line of vision, in others relative to the current position of our hand, but in any case always relative to our own body. But is this always true? Saturday evening at a well-attended stand-up party. Servers are balancing trays of appetizers over the heads of the guests. We spot donuts on one of these passing serving plates and decide in a matter of seconds to go for the one on the far right. But then the waitress briefly disappears from our field of vision, only to reappear elsewhere. How does our arm know where to reach? Relative to our body, our favorite donut has changed its position in the meantime.

However, its position relative to the tray on which the donut is lying remains constant. Can our brain make use of this fact? How and where does our brain process the different spatial information in order to be able to successfully carry out targeted movements, such as reaching for the donut? If we imagine a spatial coordinate system, its origin or zero point can be either body-related (direction of gaze, position of the hand, arm, center of the body) or object-related (position, size or orientation of the object in space). It was previously assumed that body-related reference systems are processed in different areas of the brain than object-related ones and that only body-related reference systems play a role in the planning of arm movements.

This classical model needs to be re-evaluated, as the current study by the research group at the Primate Center makes clear. To find out which coordinate system underlies the planning of goal-directed movements, they trained two rhesus monkeys to memorize movement goals on a touchscreen in order to reach for them later. As a result, the researchers found that the processing of spatial information is less a question of brain area than of cognitive demand and can be dynamically adapted. In addition to understanding elementary brain functions, the results are also important for the development of neuroprostheses. The activity of the nerve cells determines for the motor prosthesis to which target a movement is planned. "If a robotic arm is to be controlled, the information relative to which position in space the arm is to be moved upwards to the right, for example, is essential," explains Alexander Gail, head of the Sensorimotor Research Group and the study. "Correct control depends largely on describing the movement in the correct coordinate system." Future studies should clarify the question of whether and to what extent coordinate systems that are defined by the space around us also play a role in the planning of targeted movements in these brain regions when we move through space ourselves. The manufacture and development of neuroprostheses is closely linked to developments in other specialist areas such as microsystems technology, nanotechnology, IT and biotechnology, as well as the associated materials and substances. According to the current state of the art, neuroprostheses can be used to compensate for illnesses that result in considerable physical limitations and enable affected people to maintain or restore their quality of life.

Sources

Position- and scale-invariant object-centered spatial localization in monkey frontoparietal cortex dynamically adapts to cognitive demand https://www.nature.com/articles/s41467-024-47554-4

Fraunhofer-Institut für Biomedizinische Technik https://www.ibmt.fraunhofer.de/de/ibmt-kernkompetenzen/ibmt-biomedizintechnik/ibmt-medizintechnik-neuroprothetik.html

Institut für Mikrosystemtechnik Universität Freiburg https://www.imtek.de/professuren/bmt/forschung/neuroprothetik

Universitätsklinikum Heidelberg, Studie zur Verbesserung der Greiffunktion bei Tetraplegikern mittels Neuroprothesen https://www.klinikum.uni-heidelberg.de/zentrum-fuer-orthopaedie-unfallchirurgie-und-paraplegiologie/klinik-fuer-paraplegiologie-querschnittzentrum/forschung/klinische-studien/neuroprothese/