The Discovery of Spectral Opponency in Visual Systems and its Impact on Understanding the Neurobiology of Color Vision

The two principal theories of color vision that emerged in the nineteenth century offered alternative ideas about the nature of the biological mechanisms that underlie the percepts of color. One, the Young-Helmholtz theory, proposed that the visual system contained three component mechanisms whose individual activations were linked to the perception of three principal hues; the other, the Hering theory, assumed there were three underlying mechanisms, each comprising a linked opponency that supported contrasting and mutually exclusive color percepts. These competing conceptions remained effectively untested until the middle of the twentieth century when single-unit electrophysiology emerged as a tool allowing a direct examination of links between spectral stimulation of the eye and responses of individual cells in visual systems. This approach revealed that the visual systems of animals known to have color vision contain cells that respond in a spectrally-opponent manner, firing to some wavelengths of stimulation and inhibiting to others. The discovery of spectral opponency, and the research it stimulated, changed irrevocably our understanding of the biology of color vision.     

Pioneers of Affective Neuroscience and Early Concepts of the Emotional Brain

Views on the representation of emotion in the brain, as formulated about a century ago, are described, with a focus on the Vienna physiologist and psychologist Sigmund Exner, the psychoanalyst Sigmund Freud, and the French physician Israel Waynbaum. All three can be characterized as forerunners in the field of “affective neuroscience”. By the turn of the century, they had developed a neural network theory of emotion which included a stage of pre-cortical processing. In spite of their otherwise very diverse theoretical backgrounds, their concepts of parallel processing routes were highly similar. It is interesting to note that their ideas were on line with present-day views on the neural substrates and physiological characteristics of emotional processing, although none of the three scientists could rely on the refined anatomical knowledge available nowadays.