The current book starts with an overview of the past, by providing a brief history of how transcranial electrical stimulation has been used to enhance cognition and improve health. The rest of the book discusses current knowledge in the field, and provides an excellent overview of different lines of research, such as those in animals, healthy humans, and patients. The aim of this last chapter is to discuss further directions for research in the field of transcranial electrical stimulation (tES).
Over the different chapters it becomes clear that research using tES has demonstrated improvements in different cognitive and non-cognitive functions, ranging from perception and motor movement to attention, working memory, language, and mathematical abilities. These results show that such improvements are not limited to typical populations but can also affect young adults and the elderly, and neurological and psychiatric patients. These results are indeed promising, but suffer from some limitations that have been discussed in various of these chapters, as well as elsewhere (Pascual-Leone, Horvath, & Robertson, 2012; Rothwell, 2012). Some of these limitations include low sample size, artificial tasks with reduced ecological validity, lack of consistency in the montage that led to the enhancement effects, and need for replication. I will not extend the discussion on these points, as they are rather trivial and are not limited to the current field. Instead I will discuss what I perceive as the directions in which the field of tES should, and hopefully will, go. It was difficult deciding which sections to include in this respect, and I have chosen to limit our discussion to 10 sections. I will conclude the chapter with a brief discussion of the challenges that the field is facing.