As a communication and control system, a brain-computer interface (BCI) establishes a real-time interaction between the user and the outside world. Human BCI experience to date has been confined almost entirely to electroencephalographic (EEG) studies and short-term electrocorticographic activity (EcoG) studies. A BCI records brain signals and processes them to produce device commands. This signal processing has two stages. The first stage is feature extraction, the calculation of the values of specific features of the signals. The second stage is a translation algorithm that translates these features into device commands. The eventual extent and impact of BCI applications depend on the speed and precision of the control that can be achieved and on the reliability and convenience of their use. Simple BCI applications appear to have a secure future in their potential to make a difference in the lives of extremely disabled people.

Interest in activity-dependent spinal cord plasticity is increasing with the growing recognition that the acquisition and maintenance of normal motor performances reflect activity-dependent plasticity at multiple sites throughout the central nervous system (CNS), including the spinal cord. This chapter addresses the range of activity-dependent plasticity during normal life. The behavioral effects associated with spinal cord plasticity appear to reflect the interaction of plasticity at both spinal and supraspinal sites. The substantial capacity for activity-dependent plasticity in the spinal cord has important theoretical and practical implications. The substantial capacity suggests that most motor skills that are acquired gradually through prolonged practice involve spinal cord plasticity. The ubiquity of activity-dependent plasticity and the inevitable interaction between primary, compensatory, and reactive types, implies that functional effects may change over time. Early gains will not always evolve into long-term improvements, while deleterious early effects may give way to long-term benefits.