Seeking the Right Answers About Right Brain-Left Brain

Abstract

For more than 150 years, scientists have known that the left and right sides of the human brain are not identical. Some structures exist in both hemispheres but differ in size, and many functions are different on the left and the right. We refer to this difference as hemispheric specialization or, more generally, brain lateralization. From the time this lateralization was discovered, it was assumed to be unique to humans. Associated by scientists with our use of language and our ability to make tools, the lateralized brain was seen as humanity's crowning glory, elevating us above all other species. Initially, as we will see, research seemed to bear out this conclusion, but recent discoveries have not been kind to the theory of uniquely human brain lateralization. Some species of parrots are 90 percent left-footed, fish of some species all turn the same way when encountering a barrier (the better to school), and monkeys express fear more strongly on the left sides of their faces. This same research, and a great deal more, has immensely complicated our view of lateralization and its significance for language, movement, emotions, and attention, to name just a few of the affected functions. Popular psychology is rife with interpretations - and misinterpretations - of brain lateralization. You might read that people are either "left- or right-brained," and correspondingly more analytical or intuitive, more cerebral or emotional. You might read, too, that left-handers are right-brained, and vice versa. Further complicating the picture are deep and abiding beliefs about hand preference, including sometimes intense prejudices against left-handed people. At the beginning of the 21st century, the real significance of brain lateralization is still being sought.