Recording from Individual Neurons
As we have already seen, it’s possible to record the activities of a single neuron; it’s also possible to stimulate the neuron and observe the result. So far, we’ve focused on what these recordings can tell us about neurons in general—for example, how the flow of ions can produce an action potential. Similar methods, however, can be used to study how specific neurons function in a particular setting.
For example, the technique of single-cell recording has told us a great deal about the brain mechanisms crucial for vision. In a typical study using this procedure, researchers monitor the moment-by-moment activity of individual neurons in the brain while placing various stimuli in front of the animals’ eyes. The data indicate that some cells function as “motion detectors”; they fire rapidly when a moving stimulus is in view, but not when the stimulus is stationary. Other cells seem to function as “shape detectors,” firing more rapidly whenever a particular form is in view. Still other cells have their own specialties. Overall, though, the data obtained through single-cell recording allow us to identify the apparent function of each neuron, and so guide us toward a broader understanding of how individual cells contribute to the overall processes of visual perception.
It’s also possible to collect single-cell data from many individual neurons at the same time—through a procedure known as multi-unit recording. This procedure uses micro-electrodes to record the activity of individual cells and then relies on computer analyses to examine patterns of activity across the entire collection of cells. Studies of this sort can record from hundreds of neurons simultaneously, providing information about how each cell is influencing the others as well as information about the aggregate pattern of responding (e.g., Lebedev & Nicolelis, 2006). As one example, multi-unit recordings have been used to monitor activity in brain areas that animals ordinarily use to control their limbs, and then the recordings have been used to control artificial limbs. This extraordinary advance may soon lead to technology in which humans who have been paralyzed can control robotic arms and legs simply by thinking about the relevant movements!