Nature Sub-Journal: Why is the age of the direction of the worse? It turned out to be a "compass" that disturbed the brain.

Some people have a good sense of direction, while others can't remember the way.and the sense of direction usually weakens with age. Therefore, it is more difficult for the elderly to make spatial positioning than the young people, especially in unfamiliar environments.what is the reason for this? Recently, researchers from the German Center for neurodegenerative diseases (dzne) and experts in the United States have provided new insights into the causes of this phenomenon.according to their findings, the main source of spatial location errors was that "noise" disturbed the brain's "compass", resulting in inaccurate perception of movement speed.the results published in nature communications may help to develop diagnostic tools for early detection of Alzheimer's disease.from visual stimulation to muscle feedback, to signals transmitted by the vestibular system, the human brain uses a variety of sensory inputs to locate and guide us through space.an important part of information processing occurs in the entorhinal cortex.in this region of the brain located in both hemispheres, there are special neurons that can generate psychological maps of the physical environment.as a result, real-world information is transformed into a data format that the brain can process.the human navigation system works well.but this is not without defects.dzne scientists led by Professor Thomas wolbers, chief researcher of the German Center for neurodegenerative diseases, cooperated with experts from MIT and the University of Texas at Austin to design a specific experiment.a total of about 60 young and old people with cognitive health experienced virtual reality environment from the first person perspective through head mounted display (HMD).when participants move in the real world, their posture (position and viewing direction) will be tracked by Vicon motion tracking system and converted into motion in virtual environment (i.e. posture change), so that they can walk in the virtual world, and use body based visual cues and visual self cues to estimate their changing positions.for the path integration task, participants were asked to track their own position and direction by grasping the stick in the hands of the experimenter and moving along 10 different predefined but unmarked bending paths (see figure below).each path has four intermediate stops, and participants are asked to stop and report their estimation of the direct distance and direction to the starting point of the path.each participant performed three repetitions for each path. in addition, a subset of the six paths is executed three times, not in the middle of the first three stops, but only at the end of the path. as important as experimental setup is to model the measured data mathematically. this is based on a method of describing the influence of the location of the interference as noise. wolbers said: "the human body and its sensory organs are far from perfect. therefore, information processing in the brain is affected by small faults, which can be understood as noise. with our mathematical model, we can find out the influence of various error sources and determine which distortion positions are tracked most and which have the least influence. this error source has never been studied in such detail. "the results show that the errors in path integration are mainly caused by" internal noise accumulation "in information processing, and this phenomenon may be the result of inaccurate motion speed perception. "it should be noted that humans intuitively estimate the distance covered based on the time and speed of their previous walk. however, our research shows that the key source of error in determining the position is not the perception of time, but the random fluctuation of speed information entering the brain. "wolbers said. moreover, this source of error is dominant in both young people (average age 22 years) and adults (average age 69 years). "young subjects are generally better at orienting than subjects in older studies. more importantly, internal noise increases with age. this phenomenon is obviously the main cause of insufficient path integration, and may also be the cause of age-related orientation problems. however, we do not know the exact source of this noise and why it increases with age. "previously, wolbers found that some neurons in the entorhinal cortex (so-called grid cells) are essential for spatial navigation in cognitive healthy elderly people, and they emit irregularly (their activity is unstable), which is related to age-related orientation difficulties. the current results show that the instability is not caused by the fault of the grid cell itself, but by the external noise. therefore, the problem is not the grid cells, but the information flow to the entorhinal cortex. this indicates the possibility of early diagnosis of Alzheimer's disease. "Alzheimer's disease is related to the damage of entorhinal cortex in the early stage. therefore, it is reasonable to think that the disorientation shown in Alzheimer's disease originates from this region of the brain, which is different from age-related disorientation, which is our current view. "wolbers explains," this can provide an opportunity to differentiate normal age-related orientation problems from those caused by Alzheimer's disease. in the long run, our goal is to develop diagnostic methods that can detect Alzheimer's disease at an early stage. "end reference: [1] noise disturbs the brain's compass