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Auditory and Vestibular Brainstem / Mapped Potential Evoked Potentials
Evoked potentials are brain electrical signals that are produced in response to a sensory stimulus. Depending on the applied stimulus and the brain processing they can be classified in those that are due simply to an external physical stimulus (exogenous) and those that are associated with that physical stimulus and are related to psychological (endogenous) processes.
The auditory evoked potentials (PEA) are the result of recording the electroencephalographic activity triggered by the presentation of a continuous and periodic acoustic stimulus. The stimulus is highly frequency specific, which allows for selective responses.
One of the great advantages of this technique is the way in which the stimuli are presented, since it allows us to evaluate several frequencies of the audiogram simultaneously and in both ears at the same time.
Auditory evoked potentials. The auditory evoked potential (PEA) is triggered by the application of a brief sound stimulus, known as “click”, through the application of pure frequencies, a process known as tonal stimulation, or by stimulation with phonemes. They are caused by the electrical activity that the stimuli cause throughout the sensory trajectory that includes the ear, the auditory nerve and the regions of the cerebral cortex related to the hearing.
The characteristics of the PEA depend on factors associated with the stimulus, the acquisition of the PEA itself and the subject. Among the first ones are the intensity, duration, type of stimulus applied, stimulation frequency, type and location of the transducer, acoustic polarity and whether the stimulus is stereo or monophonic. The acquisition partners are of a technical nature such as the type of electrodes, their specific location and their proximity to the source, the amplification of the electrical signals and the processes to which they are subjected, such as filtering, premediation and digital processing . Factors related to the subject may be pathological (hearing loss in the middle ear or cochlea, dysfunction of the eighth nerve, brain stem or auditory cortex) and non-pathological (age, gender, alertness, body temperature , Muscle activity, presence of drugs in the body).
In the case of the potentials to provoke an evoked potentials (VbEP) stimulation of the vestibular system that triggers the PEVest requires a strong stimulus of acceleration to the head, but of very short duration so that it can be considered an impulse.
Accelerating efficiently a mass of the consistency, size and vulnerability and weight of the human head, implies several practical and safety problems, among which are the generation of the stimulus, the subjection of the head, the efficient transmission of the acceleration , Through an automated pendular armchair with a rotating stimulus in the form of a ramp of 240 grds / sec2 to the right and left, with the strictest safety standards for the subject.
It should be noted that in this case, due to the stimulation form, other component signals can also be found in the total captured EEG signal, some of which could also be considered as PE produced by external stimuli. Some of these other PEs are the sound of the acceleration, the change of the visual field due to the spin, the sensorial stimulus produced by the acceleration mechanism, etc. Also, some internal stimuli such as mental processes can produce similar effects, but these latter signals can not be identified or clearly related to the stimulus that triggers them since there is no reference signal to synchronize them, nor is there a recognizable impulse that generates them .
It is performed:
Electroencephalographic mapping in 21 monopolar referral channels with binaural reference, with the patient at rest with closed eyes and in waking state.
Electroencephalographic mapping in 21 monopolar lead channels with binaural reference, under complex stimulation, hyperventilation, visual and auditory.
With absolute and relative power evaluation per channel. Z-Score of the patient with respect to the Data Bank.
Evoked potentials (VbEP) mapped in 8 shunt channels with a rotational stimulus in the form of a 240-grds / sec2 ramp to the right and left.
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