The Pope and grandmother--a frog's-eye view of theory

Perception of color in primates: A conceptual color neurons hypothesis

Perception of color by humans and other primates is a complex problem, studied by neurophysiology, psychophysiology, psycholinguistics, and even philosophy. Being mostly trichromats, simian primates have three types of opsin proteins, expressed in cone neurons in the eye, which allow for the sensing of color as the physical wavelength of light. Further, in neural networks of the retina, the coding principle changes from three types of sensor proteins to two opponent channels: activity of one type of neuron encode the evolutionarily ancient blue-yellow axis of color stimuli, and another more recent evolutionary channel, encoding the axis of red-green color stimuli. Both color channels are distinctive in neural organization at all levels from the eye to the neocortex, where it is thought that the perception of color (as philosophical qualia) emerges from the activity of some neuron ensembles. Here, using data from neurophysiology as a starting point, we propose a hypothesis on how the perception of color can be encoded in the activity of certain neurons in the neocortex. These conceptual neurons, herein referred to as 'color neurons', code only the hue of the color of visual stimulus, similar to place cells and number neurons, already described in primate brains. A case study with preliminary, but direct, evidence for existing conceptual color neurons in the human brain was published in 2008. We predict that the upcoming studies in non-human primates will be more extensive and provide a more detailed description of conceptual color neurons.

The brain on itself: Nobel laureates and the history of fundamental nervous system function

The Nobel Prize in Physiology or Medicine has been given in recognition of work in the neurosciences a number of times. Laureates have been awarded for work on both fundamental and more complex nervous system functions. This review is restricted to contributions by 20th century laureates to the understanding of fundamental nervous system function on the cellular level. In 1906, Camillo Golgi and Ramón y Cajal were awarded for their work on the microscopic structure of the nervous system. Their achievement and those of others within this field, coupled with technological progress, gradually allowed more complex physiological studies. In 1932, the prize was awarded to Charles Sherrington and Edgar Adrian for their discoveries of how neurons function. They were followed in 1944 by Herbert Gasser and Joseph Erlanger who uncovered the highly differentiated functions of single nerve fibers. Alan Hodgkin and Andrew Huxley were awarded for the detection of the ionic mechanism of the action potential and its mathematical explanation in 1963. In 1991, Erwin Neher and Bernd Sakmann were awarded for their work on single ion channels. Although the scientists who proved the hypothesis (Fridjof Nansen, Wilhelm His, and August Forel) were never awarded by the Nobel Committee, their studies gave rise to one of the most fundamental questions in 20th century neuroscience: How is information carried from one neuron to another or to an effector cell? This was first solved in the vegetative nervous system, and, in 1936, Henry Dale and Otto Loewi received the prize for their discoveries relating to chemical transmission of nerve impulses. In 1963, John Eccles was awarded the prize for his work on the physiology of synapses. In 1970, Bernhard Katz received the Nobel Prize for the discovery of quantal release. Katz shared the prize with Julius Axelrod and Ulf von Euler, who were central in finding that transmitters are stored in presynaptic vesicles and that the effect in many synapses is terminated by reuptake. This review does not include 21st century laureates, although the prize has already been given to neuroscientists twice this century; Arvid Carlsson, Paul Greengard, and Eric Kandel received the award in 2000 for their discoveries related to signal transduction, and Richard Axel and Linda Buck received the award in 2004 for their work in the field of odorant receptors and the organization of the olfactory system.