Forensic Services – QEEG Brain Mapping and Evoked Responses
Neurometric Brain Mapping is a clinical diagnostic tool which measures brain dysfunction. It points to areas of dysfunction, quantifying its specific abnormalities and assists in the differential diagnosis process.
Neurometric refers to the use of computerized technology to acquire, score, and interpret electrical activity generated by groups of neurons from various regions of the brain. Neurometric Analysis is a valuable tool used in the Assessment of an individual's electro-neurophysiological state. It utilizes two types of physiological tests - the EGG/QEEG and a variety of Evoked Potentials. The QEEG is a statistical modification of the conventional EEG that greatly enhances it ability to detect certain brain dysfunction. Several Evoked Potential tests are utilized as part of the Neurometric Analysis, including visual, cognitive, auditory and Somatosensory. Evoked Potentials can be performed as an adjunct to clinical Assessment, and Neurometric Analysis as a whole assists in ruling out organic versus psychological and/somatic etiologies. In general, Neurometric testing provides insight about the functional capabilities of patients; sensory/perceptual and low level cognitive processes which may be difficult to determine by behavioral methods alone for certain populations.
In their 1990 report of Congress, The National Advisory Mental Health Council stated…. "In the practice of clinical neurophysiological classic EGG will undoubtedly be replaced by (QEEG) and topographic mapping. The enhanced value of these techniques will place mapping systems in virtually every major hospital, since these techniques offer the possibility of more accurate and quantified diagnosis at a much lower cost than neuromagnetic imaging, positron emission topography, or magnetic resonance imaging. It is not unreasonable to expect that it may be possible to predict a patient's clinical response to a therapeutic regimen. Adverse change in brain function may be detected in advance of clinical deterioration, thereby permitting timely therapeutic or preventive strategies."
The American Board of Electroencephalography and Neurophysiology, recognizing the importance and need for Quantitative EEG, has instituted a program of competency examinations for technicians administering these tests.
The following test - QEEG and Multimodal Evoked Potentials - are components of the Neurometric Brain Mapping protocol for the Assessment of neurological and neuropsychiatric disorders. Those test are evaluated not just by themselves, but against each other, thus contributing to a better Assessment of global brain functioning.
This test is conducted identically to conventional EEG testing, containing record portions in the eyes open state, the eyes closed state, hyperventilation, and during photic stimulation.
However, unlike conventional paper EEG, Neurometric testing utilizes computerized methods of data acquisition and review.
Prior to data acquisition, electrodes, distributed in the 10-20 International System configuration, are applied to the patient's head. A small drip of hypoallergenic conductive gel is placed into each of the 21 electrode sites until an acceptable connection is made. Raw EEG data is stored on an optical disk, affording the ability to review uninterpretal data with a montage and parameter setting of choice after the patient is dismissed. The ability to manipulate EEG information in this fashion results in shorter testing times and an increased ability to detect and localize anomalies.
Once the data is stored, it is possible to statistically analyze, and thus, to quantify the EEG (QEEG). Artifact free portions of the EEG are selected and statistically analyzed by the computer. The quantified information of the individual patient's data is statistically compared to an age matched normal population. QEEG determines a deviation from normal measure called a "Z-score." Combinations of these deviations can activate certain clinical discriminant classifications which aid in diagnosing Major Affective Disorders, Head Trauma, Learning Disabilities, Schizophrenia, Dementia, and Obsessive Compulsive Disorder.
Discriminant functions provide a quantitative estimate of the similarity between a patient's profile and characteristic patterns found during extensive research on groups of patients with various disorders.
This classification is a multivariate statistical summary of a neurometric evaluation and serves only as an adjunct to other clinical evaluations.
Topographical Brain Maps
The results of the QEEG and most of the Evoked Potentials can be printed in the form of colored two and three dimensional brain maps. These maps are a visual representation of statistical values resulting from computerized analysis. Brain maps help illustrate the location and degree of brain dysfunction, and can be especially useful to physicians for discussing test results with patients and/or their families. Although the brain maps can be a useful representation of organic dysfunction, proper interpretation of the data places emphasis on statistical information presented in the numerical tables. Brain maps should always be used in conjunction with the tables so that more definitive depiction of an individual's disorders are obtained.
Documenting Therapeutic Recovery
Neurometrics is also particularly useful when follow-up testing is necessary. Repeat testing is generally useful for evaluating medication effectiveness, degenerative dysfunction, and behavioral versus organic improvement. The information from the first test is compared to the information from the second test and is quantified as a T-score. For example, if a physician were examining a degenerative illness such as dementia, the rate or progression in the afflicted region of the brain could be realized upon retesting.
EVOKED POTENTIALS (EP) OR EVENT RELATED POTENTIALS (ERP)
An Evoked Potential is a quantified electrodiagnostic test used to evaluate functional anomalies in the peripheral and central nervous systems. Evoked potentials evaluate the state of these systems by presenting an external stimulus and eliciting a particular response. The propagation of impulses are recorded at specific sites along the neurological pathway and the corresponding area of the sensory cortex. Each Evoked Potential test focuses on particular responses from primary areas of the brain to asses the integrity of particular neural pathways and centers. Evoked responses are elicited by means of repetitive changing stimuli, such as light flashes, reversing patterns, varying tones, clicks, and tactile stimulation. The results of Evoked Potentials aid in determining an array of visual impairments including those related to motor vehicle accidents, hearing loss, tissue damage, attention deficits, memory loss, and a host of other problems. By this method, the level of involvement and determination of even minor degrees of neurological insult can be quantified. These test are purely objective and provide information that can be replicated and repeated at varying dates to assess either recovery rate or progression of damage. There are four primary types of Evoked Potentials: visual, cognitive, auditory and Somatosensory. Below is an explanation of each type.
Auditory Evoked Potentials (AEP)
These methods evaluate the status of the auditory nerve, brainstem, and cortical auditory sensory pathways. Auditory Evoked Potentials assess the structural and functional integrity of the auditory nerve, brainstem pathways, and midbrain, thalamic, and cortical structures involved in processing auditory information. The Auditory Brainstem Evoked Potential (ABSEP or BSEP) assesses the integrity of the system from the peripheral ear to the mid brain regions for each ear, separately, against a control procedure. The ABSEP provides an index of conductive and separately, against a control procedure. The ABSEP is unaffected by medications effects and state of the patient, and is insensitive to the effects of anoxia/hypoxia. Different intensity levels can be used to establish a hearing threshold. Other AEP analyses can be used to evaluate general cortical responsiveness to stimulation as well as audiometric analysis to determine finer grade hearing loss.
Cognitive Evoked Potentials (P-300)
Cognitive Evoked Potentials are electrophysiological responses related to meaning or significance of a stimulus, and are typically conducted by means of counting the occurrence of a target stimulus in random presentation with non-target stimuli. These tests are broken down in to two categories - auditory P300 and visual P300. Categorizing the P300 is especially useful for detecting processing difficulties of auditory or visual stimuli often seen in children suffering from Attention Deficit Disorder. In addition, latencies produced by the P300 have relevant implications for the Assessment of schizophrenia, generalized dementia, and short term memory loss resulting from automobile accidents or prolonged alcohol and drug abuse. More generally, cognitive Evoked Potentials reflect information about specific neural structures and disease, and they specify location and severity of damage to the nervous system. In the presence of a cognitive dysfunction, either a longer response time, nonreplication of responses, or an absence of the required response occurs.
Visual Evoked Potentials(VEP)
These procedures evaluate the visual system from the optic nerve to the occipital lobes of the brain. Each eye and/or visual field can be evaluated separately. VEP waveform morphology, amplitude and latency vary as a function of stimulus characteristics of intensity, contrast, number, and size. The P100 component of the evoked response is the most clinically useful aspect for determining visual functioning. If a patient is unable to focus on a target stimulus, LED flash goggles or an alternating luminating flash are utilized for simulation of the visual field. If a patient is able to focus, pattern reversal stimulation of various checkerboard sizes allows evaluation of visual acuity and pathway integrity. Pattern reversals are performed by means of a TV monitor with shifting checker board patterns. In general, Visual Evoked Potentials are often used to evaluate problems like double vision, attention deficits, or damage to the optic nerve.
Somatosensory Evoked Potentials (SSEP)
Somatosensory Evoked Potentials examine minute electrical nerve impulses from peripheral sense organs to central cortical receiving regions. When nerves are stimulated at the periphery, impulses can be observed as they approach the nerve root, as they ascend up the spinal Chord and as they reach the contralateral sensory cortex. By amplifying the voltage of nerve impulses, measurement of nerve volleys at specific areas along the sensory pathway are depicted. This enables interruptions and delays to be detected and localized. Sensory pathways are examined by stimulating specified nerves (generally large mixed nerves) in the upper and lower extremities. Responses are recorded at various peripheral locations including spinal entry points, the brainstem and cortical regions. The nerves stimulated most frequently are the posterior tibial nerve, the common peroneal nerve, the sural nerve, the ulnar nerve and the median nerve. Upper extremity testing of the median nerve (a nerve in the wrist) is particularly useful for determining documented high cervical neck injuries, and when combined with a Brainstem EP an VEP can assist greatly in diagnosing Multiple Sclerosis.