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The Visual Neuroscience Laboratory can trace its roots back to the earliest humans who wondered about the phenomenon of vision. As in any other branch of science, small discoveries compiled over time have led to some preliminary understanding about many of the structures and processes involved in vision. As you can see from the timeline, many seemingly isolated scientific events have contributed to this body of knowledge.
The most significant developments in single neuron electrophysiology include the work of Lord Adrian, Keffer Hartline, and Horace Barlow. Lord Adrian (E.D. Adrian, 1926) was the first to record action potentials traveling in sensory nerve fibers from the skin to the brain. His showed that each nerve fiber in the skin responded to a particular type of stimulus, and that the intensity of the response depended upon the intensity of the stimulus. His results confirmed earlier anatomical studies, which maintained that nerves connected physical stimuli with sensation, and validated Muller's doctrine of specific nerve energies , and laid the groundwork for examining the activity of neurons at higher levels of sensory pathways.
Keffer Hartline (1938, 1940) devised methodology for recording from individual retinal ganglion cells of the horseshoe crab using insulated metal microelectrodes and an amplification system, an effective technique still in use today in many laboratories, including ours. Hartline showed that stimulation of an appropriate area of the retina elicits a vigorous response from a ganglion cell; Horace Barlow (1953) demonstrated that if the surrounding area is simultaneously stimulated, the response of a given cell is reduced or even abolished! These discoveries set the stage for more detailed examination of individual visual system neurons, including those in the thalamus and cortex.
Barlow (1972) published his elegant work on a ãneuron doctrine for perceptual psychology.ä In it, he stated his position that ã...our perceptions are caused by the activity of a rather small number of neurons selected from a very large population of predominantly silent cells. The activity of each single cell is thus an important perceptual event and it is thought to be related quite simply to our subjective experience. The subtlety and sensitivity of perception results from the mechanisms determining when a single cell becomes active, rather than from complex combinatorial rules of usage of nerve cells.ä This theory, and Barlow's own research, gave rise to investigation by many laboratories of what single visual cortical neurons can ãseeä, and how they might pass that information on to areas of the brain where what we recognize as images are formed.
The direct inspiration for the work of this laboratory dates back four decades, to the pioneering work of Horace Barlow, Russell De Valois, David Hubel, and Torsten Wiesel. Their work in the primary visual cortex of cats and monkeys led to the discoveries that individual neurons in that area of the brain are selective for many stimulus dimensions: orientation, direction of movement, spatial and temporal frequency, and contrast. Subsequent work by those groups, and by our laboratory, has shown that these selectivities involve both linear and non-linear mechanisms, and we have recently been able to demonstrate that the time courses of these responses are very rapid, on the order of 20 ms. |
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