A quantitative measure of cortical organization of upper limb torque generation

The objective was to use high resolution electroencephalography (EEG) to examine the functional organization of the human sensorimotor cortex during voluntary muscle activation of the upper limb. It was hypothesized that separate centers of cortical be responsible for generating joint different directions. Furthermore, it was anticipated that the magnitude of the electrical brain activity scales with joint torque level, while preserving the location of brain activity, which depends on direction in which a torque is generated. A secondary goal was to develop a new analysis technique to rigorously quantify electrical brain activity. A novel quantitative analysis technique incorporating a realistic, subject-specific boundary element method (BEM) head model was devised to create a 3D spatial resultant vector representation of the cortical region(s) of activation. Results indicate that a clear spatiotemporal relationship exists between the location of cortical activity and the magnitude of joint torque generation. Findings also demonstrate the methods developed as part of this study provide the ability to distinguish separate locations of centers of cortical activity not only as a function of joint but more importantly as a function of joint torque direction at a given joint. In conclusion, subject-specific quantitative spatial resultant vector analysis may prove helpful in identifying cortical regions responsible for generating specific joint torque conditions and associated muscle activation patterns. The work may also prove useful for evaluating potentially contrasting motor encoding schemes for cortical neuronal systems; thus distinguishing torque direction/magnitude coding from muscle activation based encoding approaches.