Neural Recording

Neural recording is a method of observing neural activity. It has provided neuroscience with a picture of how the nervous system works.

The collective activity of many brain areas, some containing almost 100,000 neurons per cubic millimeter of tissue, allows the nervous system to mediate our sensory perceptions, thoughts, decisions, and movements. These neurons communicate with one another via synaptic connections, of which there are upwards of one hundred million in the same cubic millimeter. With so many neurons, so tightly packed together, how can we possibly observe their activity?

A major problem in studying neural activity is that in most animals, the brain is enclosed in a hard bony skull. This has led to various noninvasive approaches to record the activity of neurons, such as electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). Although a major advantage of these noninvasive techniques is that they can easily be used on human subjects, they can only measure the aggregate neural activity of a large volume of brain tissue. Another limitation is that while neural activity occurs on millisecond time scales, the metabolic signals measured by some of these techniques are extremely slow by comparison. Therefore, at the current level of technology, noninvasive techniques are unable to capture the activity of single neurons at millisecond time scales because of their low spatial and temporal resolution.

It is possible to achieve much higher resolutions if the activity of single neurons is directly observed through optical imaging or electrical recording using very tiny electrodes (microelectrodes). These are invasive methods that require opening the skull or other bony compartments and exposing the brain. Optical imaging records the activity of neurons by capturing the light emitted by certain molecules in response to electrical or chemical changes during neural activity. Although its current limitations include the restricted depth of accessible tissue and the inability to be easily used in freely moving animals, optical imaging has the potential to surpass microelectrode recording in its ability to provide high-resolution neural recordings. At present, however, recording neural activity using microelectrodes has the highest spatial and temporal resolution.

To understand the neural basis of perception, neural recordings have been performed on a diverse set of species, each having certain advantages and disadvantages: insects and lower animals have accessible nervous systems, whereas mammals have similar brain structures to humans. Although neural activity can be recorded in the peripheral nervous system, this entry focuses on the use of microelectrodes to record the activity of neurons in the central nervous system.