Chief Department: Dr. Nogués Martín

Elecrophysiology laboratories offer a significant contribution to clinical neurology and provide remarkably useful information to determine the function of the brain, muscles and peripheral nerves.
Most nervous system diseases affect the function of the brain, spinal cord, muscle sensitivity or activity to some extent, producing temporary loss of strength, movement disorders, fatigue or pain, in most cases. In other cases, organs closely related to the nervous system such as sight or hearing may also be affected revealing neurological disorders. Neurophysiological examinations study the function of these organs or the transmission pathways that may reveal neurological conditions or diseases or sensory or motor function disorders.

The most frequent methods used in clinical neurophysiology described below are:

1. Electroencephalography (EEG)
2. Electromyography  (EMG)
3. Peripheral nerve conduction velocity  (PNCV)
4. Evoked potentials  (EP)
5. Brain mapping
6. Autonomic studies 
7. Transcortical magnetic stimulation (PEM)

1. Electroencephalography  (EEG)
This test is performed using an extensible cap with 20 electrodes that are held in place to the scalp with a special gel (patients must wash their hair without using conditioner before the test). The electrodes connected by wires to a recording machine detect and record the patterns of the electrical activity of the brain on a computer screen. During this test, that takes approximately 20 minutes, patients are asked to relax and be calm as they lie on a table or sit in a comfortable chair, in a peaceful atmosphere with dim lights.
FLENI has two encephalography laboratories; one for conventional studies and the other for prolonged studies which take an hour and are performed while the patient is asleep. These studies are particularly revealing because during sleep patients may show pathological conditions such as epileptic activity not evident in routine tests.

2. Electromyography (EMG)
The term electromyography is frequently used to refer to electromyography and peripheral nerve conduction velocity. Electromyography is a technique that uses electrodes to measure directly the electrical activity within the muscles. Although this test may be painless or non invasive when performed using electrodes on the skin, it is usually performed using a needle electrode inserted through the skin into the muscle. Motor unit action potentials can be recorded and displayed audibly through a speaker when muscles are voluntarily contracted. Motor unit action potential is the definition given to the electrical activity generated by muscle fibers when they respond to stimulation from a single axon. The study of frequency and amplitude of the motor unit action potentials helps to differentiate between primary muscle conditions and neurogenic disorders. The latter may be produced by lesions in the spinal motoneuron, plexus or peripheral nerves. To provide accurate information about the location of the disorder, electromyographies are often done together with peripheral nerve conduction velocity tests.
A needle electrode is also inserted into the muscle to study electrical activity at rest. When the muscle lacks innervation capacity, denervation potentials can be detected, largely revealed by fibrillation and positive acute waves.
FLENI has cutting edge electromyographers that may perform quantitative tests of the electromyogram. The units at Escobar and Montañeses centers are on line so at FLENI it is possible to discuss the studies with other healthcare centers of the world.
In the field of electromyography, FLENI was the first health center in Argentina to develop single-fiber electromyograms. Single-fiber EMG is the most sensitive electrophysiological test to detect certain neuromuscular conditions such as myasthenia gravis,   Lambert -Eaton syndrome and botulism. People all over the country call FLENI for appointments based on our expertise in single-fiber EMGs. The test consists of inserting a needle electrode in a very small detection area to record the action potential generated by a single muscle fiber. This test requires a special EMG machine and a skilled physician. Dr. Martin Nogués,  was trained at the Neurophysiology Department of The University of Upsala, Sweden, by Dr. Erik Stalsberg, the pioneer in this type of tests.

3. Peripheral Nerve Conduction Velocity (PNCV)
The nerve conduction test is the essential counterpart to the electromyography test because it locates lesions in structures that go from the spinal motoneuron to the neuromuscular junction. This test is fundamental in peripheral nerve entrapment or peripheral polyneuropathies diagnosis because it helps differentiate between motor, sensory or mixed polyneuropathies and myelin sheath, or axon involvement or both.
In most cases, this test is performed at FLENI using surface electrodes - which are small metal discs- applied on the muscle of the area for study. Stimuli are applied at different sites to measure nerve conduction velocity and identify the site of nerve injury.
FLENI’s state-of-the-art units provide computerized signal survey, automatic nerve conduction velocity calculation and compare outcomes with standard values in real time.
Nerve conduction studies also  (1) detect myasthenia gravis and other neuromuscular conduction disorders using repeated stimulation; (2) study the proximal part of the peripheral nerves using H-reflex and F-wave, and (3) evaluate  lesions in certain pairs of cranial nerves (trigeminal and facial nerves) using blink reflex testing.
FLENI also has a Medoc, TSA-II neurosensory analyzer to evaluate the function of the small myelinated and unmyelinated fibers that specifically conduct temperature and vibration sensations. These are usually involved in some common peripheral neuropathies such as diabetes neuropathy. In many of these cases, conventional conduction velocity -as described above- does not give positive results even in patients with relevant sensory symptoms. The evaluation of the thresholds and sensory levels to cold and heat and vibration studied with a neurosensory analyzer is dramatically affected in some cases and provides quite accurate diagnosis. This study is non invasive and it takes approximately one hour.

4. Evoked Potentials (EP)
 Evoked potentials tests were initially applied by FLENI at the end of the ‘70s simultaneously with the most innovative laboratories in the USA and Europe- record selective sensory information such as sight and hearing.  Using electrodes similar to the ones applied in electroencephalograms, evoked potentials procedures record the response at the brain cortex or brainstem to specific stimuli in each area using checkerboard patterns or white light in visual evoked potentials tests or short duration noises such as clicks in auditory evoked potentials tests. Evoked responses provide information for the objective assessment of the areas under study. These procedures are very useful to evaluate multiple sclerosis, hearing impairments in children or brainstem structures in comatose patients.
Other evoked potentials tests, such as the somatosensory evoked potentials, measure the conduction of certain nerve pathways through the spinal cord to the brain cortex.
Another type of evoked responses used by neurologists and neuropsychiatrists are the cognitive evoked potentials.
This evoked response, usually called P300, evaluates the perception of random phenomena such as a specific noise or word. When such phenomenon is identified, the patient “accepts” it in memory and, as a result, a parietal brain wave is recorded.
Time and amplitude of the positive wave appearing approximately 300 mseg after stimulation indicates attention integrity perception and acceptance of the phenomenon in the conscience. This evoked potential measures quite objectively the cognitive function that may be impaired in cases of dementia.
EEG Holter
The EEG Holter test has been performed for several years; however, it has evolved significantly in the near past as a result of the introduction of novel technology. FLENI has modern EEG holter units that can store up to 32 channels and a maximum of 48 hours of monitoring. To perform this test electrodes are placed on the scalp as in the EEG technique.  It is an ambulatory test that records information for one or two days uninterruptedly in a mini laser disc carried in a box on the side like a purse in normal daily activities or while the patient sleeps. Once the device is removed, the electroencephalogram in the small disc is analyzed by a computer and the data of the events is compared with recordings during activity or at rest.
It is worth mentioning, that in many cases electroencephalographic abnormalities occur in certain circumstances related to everyday life activities, such as watching TV, eating, commuting, and other situations, which are hard or even impossible to adapt to a lab environment or hours.  FLENI has two cutting edge encephalographic Holter devices with 20 channel that provide reliable information and have proved to be extremely useful in patients who, having been subject to several routine tests before, no abnormalities had been identified.

5. Brain Mapping (Quantitative EEG)
 Brain mapping is a procedure derived from electroencephalograms using conventional techniques. The basic difference lies in that the brain waves are downloaded as digital data and software such as Fourier, Gabor, etc. decodes it. A computer displays brain activity rates according to frequencies or voltages. The data obtained from each electrode applied to the scalp is displayed in bars and tables to create a “map” for each comparable group of frequencies or amplitudes. Additionally, brain mapping can build frequency ratios of different areas of the brain. Research established that variations in those ratios can indicate dementia, depression or other disorders.

6. Autonomic Tests
The autonomic nervous system (ANS) diseases laboratory at FLENI is fully equipped to evaluate the main functions of this system. Modern equipment is used to perform:
- Autonomic cardiovascular function test (non invasive).  This study measures autonomic cardiovascular reflexes, and the heart rate and blood pressure variability during respiratory changes. It evaluates heart rate and blood pressure changes during normal and deep breathing. It is performed on an examining table with electrodes held in place on the skin of the thorax and continuous blood pressure screening on the left arm. The patient breathes calmly, then, deeply and blows into a mouthpiece like in a spirometry for the valsalva maneuver.
- Tilt -Test or Response to postural change and prolonged orthostatic stress. This study is usually indicated in patients with syncope. It consists of taking patients from a flat (supine) to a standing or upright position. Patients are hooked to a tilt table while safety straps are applied across the legs and hips to hold them in place. The table is tilted up to an angle of 60 degrees as the heart rate and blood pressure of patients are continuously recorded in a computer (45 minutes maximum). The objective of this study is to record the heart rate and blood pressure response to postural change. It is indicated in patients with syncope (black out) or to study autonomic failure in neurological diseases. Patients must be controlled and monitored during the test because in case of passing out, the test must be immediately stopped and patient returned to the supine position.
– Sweat tests. This test is performed to determine the areas with no sweating or excessive sweating. The procedure consists of dusting the skin with powder to mark pathological areas, excessive sweating areas and areas with no sweating.
Frequent clinical indications for autonomic studies
- Syncope
- Loss of consciousness for unknown reason
- Orthostatic hypotension
- Parkinson’s disease (orthostatic hypotension and autonomic dysfunction)
- Multiple system atrophy
- Pure autonomic failure
- Diabetes
Peripheral neuropathies with autonomic failure: Guillain-Barré, congenial neuropathy, small fiber neuropathy, familial  dysautonomy (Riley-Day Syndrome), amyloidosis, etc.

7. Transcortical Magnetic Stimulation, MEP (TMS)
Transcortical Magnetic Stimulation ranks among the most innovative techniques in clinical neurophysiology. This method studies the descending brain motor pathways to the peripheral muscles. These descending motor pathways were inaccessible in human beings in the past and their study was limited to animal experiments using invasive methods.
Transcortical Magnetic Stimulation allows for relatively painless transcranial excitability of the motor cortex, and through it, it creates a descending reflex to the limb muscles and measures motor fiber conduction velocity (pyramidal tract) and evaluates functions that cannot be tested otherwise, except using neuroradiological methods such as magnetic resonance imaging.   Several degenerative diseases, such as amytrophic lateral sclerosis, are not identified by neuroradiological methods.  In such cases, transcranial magnetic stimulation may be the only appropriate study of corticospinal pathmays.
FLENI was the first healthcare center in Argentina to conduct these studies.
At present, FLENI has two different magnetic stimulators, one for motor studies and the other for repetitive studies. The latter are used in psychiatry, especially in depression, because they may replace electroconvulsive  therapy with the additional benefit compared to electroshocks that no general anesthesia is necessary.
Currently, this method is used in neuronal plasticity research work (an important element in strokes and spinal cord lesions, for example).