In
electroencephalography
Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...
, the P50 is an
event related potential
An event-related potential (ERP) is the measured brain response that is the direct result of a specific sensory, cognitive, or motor event. More formally, it is any stereotyped electrophysiological response to a stimulus. The study of the brai ...
occurring approximately 50 ms after the presentation of a stimulus, usually an auditory click.
The P50 response is used to measure
sensory gating Sensory gating describes neural processes of filtering out redundant or irrelevant stimuli from all possible environmental stimuli reaching the brain. Also referred to as gating or filtering, sensory gating prevents an overload of information in the ...
, or the reduced neurophysiological response to redundant stimuli.
Research has found an abnormal P50 suppression in people with
schizophrenia
Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social withdra ...
, making it an example of a
biological marker
In biomedical contexts, a biomarker, or biological marker, is a measurable indicator of some biological state or condition. Biomarkers are often measured and evaluated using blood, urine, or soft tissues to examine normal biological processes, pa ...
for the disorder.
Besides schizophrenia, abnormal P50 suppression has been found in patients with
traumatic brain injury
A traumatic brain injury (TBI), also known as an intracranial injury, is an injury to the brain caused by an external force. TBI can be classified based on severity (ranging from mild traumatic brain injury TBI/concussionto severe traumatic b ...
,
recreational drug use
Recreational drug use indicates the use of one or more psychoactive drugs to induce an altered state of consciousness either for pleasure or for some other casual purpose or pastime by modifying the perceptions and emotions of the user. When a ...
, and
post-traumatic stress disorder
Post-traumatic stress disorder (PTSD) is a mental and behavioral disorder that can develop because of exposure to a traumatic event, such as sexual assault, warfare, traffic collisions, child abuse, domestic violence, or other threats on ...
.
Paired click test
In a paired click test, one auditory click sound will be presented, followed by a second click approximately 500 ms after the first one. The second sound is considered redundant, and so a typical control showing normal sensory gating will produce a reduced response (in wave
amplitude
The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplit ...
) to the second click. The suppression is measured as the percentage of amplitude decrease in response to the second click compared to the first click, with typical controls showing an approximately 80% decrease to the second stimulus.
This response is recorded at the scalp and represents a pre-
attentive process of
sensory gating Sensory gating describes neural processes of filtering out redundant or irrelevant stimuli from all possible environmental stimuli reaching the brain. Also referred to as gating or filtering, sensory gating prevents an overload of information in the ...
.
Development
Healthy infants as young as 1 to 4 months old were found to demonstrate a P50 suppression in a paired click task, suggesting that sensory gating is present early in development.
Suppression deficits in individuals with schizophrenia
Studies have found that patients with schizophrenia fail to show a reduced response to the second click.
Abnormal sensory gating may be behind symptoms of schizophrenia such as sensory overload and difficulty concentrating.
A link exists between abnormal
α7 receptors and the abnormal P50 response.
In a family that has a child with schizophrenia, at least one of the parents tends to show higher rates of abnormal P50 gating compared to normal controls even when the parents themselves do not have schizophrenia.
Abnormal P50 suppression in paired click tests can be found through either a failure to suppress the second stimulus, or as a failure to produce a heightened response to the first stimulus. Some studies suggest that P50 suppression in people with schizophrenia might instead appear as a smaller response to the first auditory stimulus.
See also
*
Endophenotype In genetic epidemiology, endophenotype (or intermediate phenotype) is a term used to separate behavioral symptoms into more stable phenotypes with a clear genetic connection. The concept was coined by Bernard John and Kenneth R. Lewis in a 1966 pap ...
*
Prepulse inhibition
Prepulse inhibition (PPI) is a neurological phenomenon in which a weaker prestimulus (prepulse) inhibits the reaction of an organism to a subsequent strong reflex-eliciting stimulus (pulse), often using the startle reflex. The stimuli are usually ...
*
Startle response
In animals, including humans, the startle response is a largely unconscious defensive response to sudden or threatening stimuli, such as sudden noise or sharp movement, and is associated with negative Affect (psychology), affect.Rammirez-Moreno, D ...
*
P300 (neuroscience)
The P300 (P3) wave is an event-related potential (ERP) component elicited in the process of decision making. It is considered to be an endogenous potential, as its occurrence links not to the physical attributes of a stimulus, but to a person's ...
References
{{EEG
Electroencephalography
Evoked potentials
Mental disorders screening and assessment tools