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!
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