Motor intention in the posterior parietal cortex : experimental data analysis and functional modeling study

The complexity of processes occurring in the brain is an intriguing issue not just for scientists and medical doctors, but the humanity in general. The cortex ability to perceive and analyze an enormous amount of information in an instance of time, the parallelism and computational efficiency are among the questions that attract attention. Even a simple, everyday gesture, for example, reaching for a cup of coffee, evokes a flow of signals in the brain. It goes from the primary visual region, that locates the cup on the table, to the primary motor region that sends the precise coordinates to the hand, and the instruction what to do next. The sequence of signal transmission and transformation continues through several regions, sensory, associative and motor ones. In this study, we will focus on the posterior parietal cortex, the region involved in the transformation of visual inputs into the preliminary motor plans. The years of experimental work revealed mechanisms for integration of multimodal signals, coordinate transformations, information representation in multiple coordinate frames, and many other. Still, a single encompassing theory about movement generation in the parietal cortex does not exist, and is a matter of debate. This study contributes to the analysis of motor intention in the 7a parietal region. The motor intention, a high-level cognitive signal, is defined as the preliminary plan for making a movement. From the engineering point of view, encoding of motor parameters in the neural activity is extensively studied within the framework of brain-computer interfaces. The motivation behind these studies is the development of neural prosthesis for the paralyzed persons. The direct cortical prosthesis can significantly improve the lives of paralyzed people, who have lost every other contact with the outside world. Also, this framework opens the possibilities for monitoring the neural processes during the execution of natural movements, and studying the mechanisms behind it. In this work, a method for identification of motor intention from the standard recordings of neural activity, the spike trains, is developed. The data of interest was collected in a series of behavioral experiments involving reaching or saccadic eye movements. The presence and absence of motor intention was monitored in various phases of motion execution, and for different types of movements. All the recordings obtained simultaneously are combined in the same decoding session. Therefore, the analysis is done using the activity of small population of cells (typically 8 to 12 cells). We aim to study the motor intention in a general context which requires using activity of multiple cells. The population size is determined by the experimental procedure. Throughout this study we assume that the motor intention can be red from the spike rates, the assumption supported by the neurophysiological studies. Therefore, all the simultaneously collected spike trains are converted in