Just as students in a classroom might pat their neighbours on the knee and break into gossip, neurons chatter among themselves via minute pulses of electricity, its intensity ebbing and flowing, rising and falling in a wave-like manner. EEG records these brain-waves.
There are several different variations of EEG, with its rhythmic activity defined by frequency (frequency is measured in cycles per second, or Hertz). The five most well-known brainwaves are beta, alpha, theta, delta, and gamma.
Electroencephalography
For EEG, a technician places electrodes on your scalp and connects them to a computer that makes it easier for your neurologist to view patterns in your brain’s electrical activity. There’s no danger; you don’t even have to be restrained or sedated.
Your neurologist can then use all these results to diagnose you, do other tests or provide care treatment options; plus, they can tell you more about your brain function such as if you still need anti-epileptic medications, or if you’re able to stop taking your medication and other treatment plans you might need for your seizures.
The moment-to-moment dynamics measured using an EEG are ultimately a reflection of the underlying microscopic dynamics of neurons Figure 3: In modern neuroscience, spectral analysis of EEG data is the commonly used classification system. It involves measuring the different frequencies of brain waves active within a particular cognitive process: delta (0.5-4 Hz); theta (4 to 7 Hz); alpha (8 to 12 Hz) and beta (16 to 31 Hz). Other EEG waveforms, which are non-diagnostic and considered artefacts, are not useful for broad strokes diagnosis.
Electromyography
The test is called electromyography (ee-LECK-tro-my-AH-graf-ee). Your muscles and the motor neurons that connect to them send electric signals to each other. EMG converts those signals to graphs or sounds that a specialist can read. If the graphs or sounds aren’t quite right, it means your nerves or muscles aren’t working well, indicating neuromuscular disease.
In an EMG, the needle electrodes are slipped through the skin and into the muscle, where they detect the electrical activity expressed by the muscle. It’s then displayed on a monitor or projected via an audio amplifier that you can hear. Your doctor might refer you for an EMG if you have burning, tingling or unexplained weakness in your extremities. These tests are safe, though they can sting slightly or cause some bruising where the needle enters the skin. They’re usually performed in the hospital by doctors who specialise in neurology and muscle disorders, and are often combined with a nerve conduction velocity study to help pin down the source of your symptoms.
Evoked Potentials
It is measured from scalp electrodes and remote sites on the body as biphasic (having two phases) reponses that change in amplitude and latency from their baseline value depending upon the stimulation delivered. The procedure to measure an evoked potential is one in which a clinician delivers mild and painless electrical shocks to your scalp or other sites on your body.
There are many different waveforms that can be recorded and they are named for their polarity, the typical latency of their peak, and for the order in a series (eg, the N20 waveform represents a cortical response to stimulation of the median nerve). Those evoked potentials of greatest use in IOM are those that reflect transmission of an impulse up a fibre tract.
Variations of evoked potential amplitude and latency represent neurological dysfunction; a drastic decrease in cervical spinal cord SEP amplitude, for instance, can alert for upcoming injury and call for intervention. And a quick return to a normal evoked potential in the subacute phase of traumatic brain or spinal cord injury corresponds to a good prognosis.
Transcranial Magnetic Stimulation
It uses an electromagnetic coil to stimulate and ‘reset’ regions of the brain that are implicated in mood regulation. Today, the most common use of TMS is in the treatment of depression, where it has the ability to enhance the quality of life for patients who have failed to respond to antidepressants. It is also being trialled for a range of other medical problems, among them, chronic pain and tinnitus, or ringing in the ear.
This requires having the participant come in and receive TMS through the scalp, with electrodes poked through their skull into the brain. This method of obtaining data is quite imprecise compared with fMRI or even EEG. For instance, whereas a figure-of-eight coil placed over M1 excites late volleys of pyramidal cells, a double-cone coil placed over the same region selectively excites early I-waves.
A further technique that is sometimes able to assess what’s happening on the surface of the brain is to shine a laser light on the outside of the head, and to use the resultant vibrations that are generated by moving oxygen-laden hemoglobin molecules in small red blood cells whizzing back and forth, and then to integrate all that information computationally so as to produce a 3D map of brain oxygenation.