**Abstract**

In recent years, neuroscience-based rehabilitation, also known as neurorehabilitation, has been attracting increasing attention worldwide. Electroencephalography (EEG) has been widely used in clinical practice as a tool for the evaluation and treatment of rehabilitation because of its noninvasive and simple measurement of human brain activity. EEG-electromyography coherence is a method to analyze the synchronization between the motor cortex and muscle activity during movement and to quantitatively assess how the motor cortex controls muscle activity. In addition, recent advances in analysis and measurement techniques have made it possible to estimate the source of EEG signals, thus serving as a method to evaluate rehabilitation. The brain-machine interface, which integrates medicine and engineering, has been widely applied in the treatment of rehabilitation and for improving the quality of life. This chapter provides an overview of EEG, and its uses as a tool for rehabilitation assessment and treatment.

**Keywords:** EEG, non-invasive brain function measurement, rehabilitation, EEG–EMG coherence, EEG mapping, EEG source imaging, brain-machine interface

### **1. Introduction**

Ever since the first human electroencephalography (EEG) [1] and electromyography (EMG) [2] recordings were performed in the 1920s, the theoretical aspects, test techniques, and clinical applications of each have rapidly advanced [3]. Methods for imaging brain function have appeared one after another over the past century beginning with evoked potentials [4] in the 1940s, event-related potential [5, 6] and magnetoencephalography (MEG) [7] in the 1960s, positron emission tomography (PET) [8, 9] in the 1970s, and functional magnetic resonance imaging (fMRI) [10, 11] in the 1990s. Currently, the noninvasive methods available for measuring brain function are broadly divided into two categories: electrophysiological examinations and imaging techniques based on hemodynamic principles. The former includes EEG, MEG, and transcranial magnetic stimulation (TMS), while the latter includes fMRI, PET, single photon emission computed tomography (SPECT), and near-infrared spectroscopy (NIRS) [12].

EEG is widely used in rehabilitation as it is well suited to the field's demands for measurement, which includes simple, safe, and portable equipment. In the past, EEG has primarily been an analysis method used to capture brain activity

accompanying a given phenomenon or during a given task as an electric field and subsequently estimates the source of that activity based on the distribution on the scalp. In contrast, recent advancements have led to the development of a method capable of capturing fluctuations in the power of rhythms in a certain frequency band. When this power decreases accompanying a given phenomenon or task, it is called event-related desynchronization (ERD). Conversely, when this power increases accompanying a given phenomenon or task, it is called event-related synchronization (ERS) [13–15]. Thus, electric field analysis is an analysis of the temporal domain, while the second method is an analysis of the frequency domain. In frequency analysis, ERD is thought to reflect a state of increased cortical activity in the region, while ERS is thought to reflect a state of decreased activity or return to a low level. This chapter will outline the clinical applications for treatment and evaluation of rehabilitation using these features of EEG focusing specifically on EEG–EMG coherence, scalp mapping, and brain-machine interface.
