Evoked potential

An evoked potential or evoked response is a neurophysiological examination that assesses the function of the acoustic, visual, and somatosensory sensory systems and their pathways through elicited responses to a known and normalized stimulus. The response of the central nervous system to sensory stimuli is studied, analyzing the nerve pathways that provide information to the brain from the periphery.

They are usually non-invasive tests. The evoked potential designates the modification of the electrical potential produced by the nervous system in response to an external stimulation, especially sensory (a sound, an image, etc.), but also to an internal event such as a cognitive activity (attention, the preparation of the motor, etc.) and is saved through techniques such as electroencephalography (EEG) or electromyography (EMG). When a train of sensory stimuli of any kind reaches the brain, it causes characteristic wave sequences on the electroencephalographic (EEG) trace, which we call evoked potentials. They are different for each sensory modality and their variability also depends on the intensity of the stimulus. Characteristically, they present a stable relationship over time with respect to the stimulus.

Thanks to evoked potentials, various constructs can be studied.

Types of potentials

1. Sensory: It is the neurophysiological response of the nervous system to a sensory stimulus or a nervous trunk.
2. Motors: It is the answer of one or more muscles to the stimulation of a peripheral nervous trunk or of some point in the central nervous system directly or transcrananaly.
3. Reflexes: It is the motor response of a muscle or muscle group to a sensory stimulation.

Sensory Evoked Potentials

They can be classified according to the latency time and in relation to the sensory organ stimulated.

Latency time

Short: they are independent of the person's state of consciousness and are generally little modified by anesthetics if they are in the appropriate range.

Medium latency: they are intermediate potentials, in the case of auditory ones they are inconstant, and they change with the level of anesthesia.

Long latency: in general they strongly depend on the degree of cooperation of the observer and are strongly depressed by anesthesia.

In relation to the stimulated sensory organ

You can get:

• Visual evocative potentials (PEV)
  • flash flash
  • pattern

• Evoked hearing potentials
  • click
  • tonal

• Potential evoked somatosensoriales (PESS)
  • trunks
  • dermatomy

Motor Evoked Potentials

• by electrical stimulation
• by magnetic stimulation

Event-Related Potentials (ERP)

• Cognitive evoked potentials P300
• Negative Contingent Variation (VCN)
• Mismatch Negativity (MMN)