The event-related potentials (ERP) require the analysis of the cognitive activity. There are neurophysiological tests that measure the voltage or power while the patient performs tasks that demand some effort. These are fluctuations in the EEG voltage caused by sensory, motor, or cognitive events. Therefore, to see changes in the EEG a certain stimulus must be presented or a task must be carried out. These changes appear in the form of peaks and provide information about the underlying cognitive processes.

The event- related potentials are essential to assess the brain activity during tasks of:

• Attention
• Verbal memory
• Eye-to-hand memory
• Idea generation or mental flexibility
• Oral comprehension
• Reading comprehension
• Logical-mathematical processes
• Movement planning
• Visuomotricity
• Emotional processes

Therefore, these assessments have a significant contribution in the diagnosis of disorders, like attention deficit, bipolar disorder, learning problems, neuromotor alterations, etc.

P300 is likely the most important test of this group, where we show the patient an auditory stimulus and define an EEG segment. Within this segment, there will be changes in the brain electrical potential associated specifically with the stimulus. Therefore, it represents one of the evoked potentials and contributes in the assessment of the cognitive function and in the identification of alterations in different regions, particularly in the brain cortex, seen in different diseases, like autism, vascular events (infarctions), trauma, and other types of damages or malformations.

It is required to learn about the functional interaction among brain cortex regions, which is lost in brain lesions caused by different causes, as a result of axon reduction in the regions. This change generates partial or total disconnection, the consequent interaction loss, and the resulting functional deficit. These connections enable communication among the regions, which not only depends on the pyramidal neurons that generate the axons responsible of the connection but only on their regulatory counterparty, that is, the basket cell type GABAergic neurons. These are inhibitory cells responsible for turning off the transmission through the connections, an essential function to send new information packs.

This neuronal type deficit makes it impossible to turn off the transmission, generating significant disorders, like those seen in the most frequent schizophrenia type. Nevertheless, these disorders can be generated as well by exogenous events that affect the population of inhibitory neurons.