Functional Study Of Dorsal Premotor Cortex Of Monkey In Grasp Planning

Reach and grasp is one of the most important function in our daily life.Therefore,studying how the brain controls the reach and grasp movement has been one of the hotspots in the field of neural research.In recent years,with the development of brain-computer interface,it is possible to directly read the brain’s motion intents and translating them into the control commend of the external devices.This technology provides a new way of restore the lost motor function of patients.In this process,the dorsal premotor cortex(PMd)is an important node of the reach and grasp circuit which can be used as an important source of information for the analysis of the reach and grasp movement.However,the research on the function of PMd in the grasp planning process is not deep enough.It is not clear whether the specific function of PMd in the grasping planning process is visual information processing or target feature processing or decision-making or grasp preshape processing.In this paper,we focused on the following works:Firstly,we created a non-human primate training platform,and based on this platform,we designed two experimental paradigms:the hold and move turning table experimental paradigm and the single-object experimental paradigm.The turning table experimental paradigm use the illumination lamp to control whether the target object is visible to the monkey.At the same time,the chosing gesture in different trials is indicated by replacing different target object.The single object experimental paradigm uses the combine of instructed cues,and the monkeys were trained to use different decision-making styles to grasp the same target object with two gestures.Through the cross-comparison of the two experimental paradigms and the different experimental conditions of each paradigms,we separated the four kinds of information in grasp planning period:visual information,target feature information,decision-making information and grasp preshape information.After that,the neural signals of PMd were recorded synchronously,and the quantitative analysis methods of single neuron and neural population were used to analyze the function of PMd in the grasp planning process.The results showed that PMd mainly encoded the gesture preshape during the grasp planning period.The main innovations are:1)There are few studies on whether the visual stimulation of the target object affects the activity of PMd neurons in the process of grasp planning.We designed the turning table paradigm,which the grasp target will disappears during the grasp planning period.By analyzing the characteristics of the single neuron and the neural population before and after the disappearance of the visual information of the target,we found that whether the grasping target is visible has no significant effect on the neural activity of PMd.This result reveals the basic function of PMd in the grasp planning process.2)After that,the influence of target feature,decision-making and gesture preshape on PMd neural activity in the period of grasp planning was further studied.We designed a single-object paradigm that can separate the target feature,decision-making and grasp preshape element.From the results of single neuron and neural population analysis,it can be concluded that PMd has no obvious response to the target feature and decision-making during the grasp planning process,its main function is to encode the gesture preshape.Combined with previous research results,the work of this paper suggests that PMd may be involved in the control of upper limb reach and grasp movement at the same time,which provides a new idea for the research of relevant neural circuits and a new basis for the establishment of practical and efficient upper limb movement brain-machine interface system in the future.