Webcast Lectures

Presented by HHMI investigators
A. James Hudspeth, Ph.D., M.D., and Jeremy H. Nathans, M.D., Ph.D.

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Lecture One—Sensory Transduction: Getting the Message, by A. James Hudspeth

From bacteria to behemoths, organisms survive by their ability to detect important stimuli in their surroundings, such as light, sound, odor, physical contact, and temperature. "Sensory transduction" is the term applied to the process of detecting and processing stimuli. In bacteria and other single-celled organisms, light touch and chemical substances can influence the speed and direction of movement. In higher organisms, a wealth of different stimuli are transduced into electrical signals that the brain can interpret; appropriate responses then typically involve the patterned activation of various muscles. Despite the diversity of stimuli, various sensory systems share many features: organs to capture stimuli, receptor molecules to effect transduction mechanisms of amplification to enhance reception, capacity to adapt to monotonous stimuli, and intra- and intercellular means of encoding stimuli.

Lecture Two—The Science of Sight: Getting the Picture, by Jeremy Nathans

Mechanisms for detecting light as a means of obtaining information about the environment have evolved in many life forms, from simple, single-celled bacteria to complex plants and animals. In humans, detection of light begins when an image reaches the retina, a thin layer of nerve cells that lines the back of the eye. The properties of the retina, including speed and sensitivity of response and the ability to perceive color, govern much of human vision. Researchers have studied color vision intensively, in part because it varies significantly in the human population, adding interest from an evolutionary and genetic perspective. The differences in color vision among individuals are now understood to arise from genetic variations in the proteins of the retina that are responsible for absorbing light.

Lecture Three— The Science of Sound: How Hearing Happens, by A. James Hudspeth

The human ear is remarkable in its ability to discriminate various properties of sound. We can detect sounds so faint that our ear's internal components vibrate subatomic distances; we can hear sound frequencies as high as 20,000 cycles per second as distinct tones. As a result of genetic conditions, drug exposure, infection, and noise damage, however, nearly 30 million Americans suffer from hearing problems that range from mild difficulty in understanding speech to profound deafness. Remarkably, the hair cell, a single type of cell, is responsible for the ear's outstanding capabilities and for its vulnerabilities. Each hair cell is a mechanical sensor in the internal ear that responds when sound or acceleration deflects its sensitive structure, the hair bundle. Recent results indicate that the hair cell is not only the passive recipient of sound but also an active amplifier. When the amplification is excessive, human ears can actually emit sound!

Lecture Four— Neural Processing: Making Sense of Sensory Information, by Jeremy Nathans

Most people can recognize a familiar face or voice within a fraction of a second. By contrast, the most powerful computers perform such tasks poorly. How does the human brain efficiently extract information from a complicated scene or mixture of sounds? This question is especially interesting because the brain uses relatively slow computing elements (neurons) compared with the chips used by a computer. Part of the answer to this question comes from the observation that the brain divides and modifies the sensory information at each stage of processing. For example, in the visual system, different aspects such as color, motion, and depth are analyzed separately. How the various attributes of a complex sensation are divided and reassembled is an area of active research.

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