Sensory gating

Sensory gating describes neurological processes of filtering out redundant or unnecessary stimuli in the brain from all possible environmental stimuli. Also referred to as gating or filtering, sensory gating prevents an overload of irrelevant information in the higher cortical centers of the brain. The pulvinar nuclei of the thalamus play a major role in attention, and filter out unnecessary information. Although sensory gating is largely automatic, it also occurs within the context of attentional processes. Though the term sensory gating has been used interchangeably with sensorimotor gating, the two are distinct constructs.

The cocktail party effect illustrates how the brain inhibits input from environmental stimuli, while still processing sensory input from the attended stimulus. The cocktail party effect demonstrates sensory gating in hearing, but the other senses also go through the same process protecting primary cortical areas from being overwhelmed.

Neural regions involved in sensory gating
Information from sensory receptors make their way to the brain through neurons and synapse at the thalamus. The pulvinar nuclei in the thalamus function as the gatekeeper, deciding which information should be inhibited, and which should be sent to further cortical areas. Sensory gating is mediated by a network in the brain which involves the auditory cortex (AC), prefrontal cortex and hippocampus. Other areas of the brain associated with sensory gating include the amygdala, striatum, medial prefrontal cortex, and midbrain dopamine cell region (GABAergic neurons only). Research of sensory gating primarily occurs in cortical areas where the stimulus is consciously identified because it is a less invasive means of studying sensory gating. Studies on rats show the brain stem, thalamus, and primary auditory cortex play a role in sensory gating for auditory stimuli.

Paired-click paradigm
The paired-click paradigm is a common non-invasive technique used to measure sensory gating, a type of event-related potential. For normal sensory gating, if a person hears a pair of clicks within 50ms of one another, the person will gate out the second click because it is perceived as being redundant. Evidence of the gating can be seen in the P50 wave, occurring in the brain 50 ms after the click. Low values of the P50 wave indicate that sensory gating has occurred. High values of the P50 wave indicate a lack of sensory gating. Individuals with schizophrenia only reduce the amplitude of S2 by 10-20%, whereas individuals without schizophrenia reduce the amplitude of S2 by 80-90%.

Other techniques
Event-related potentials (ERP) and Magnetoencephalographies (MEG) are used to measure brain responses and are common techniques for studying sensory gating. One type of ERP used for sensory gating research is an Electroencephalography (EEG). EEG research on sensory gating shows that gating starts almost immediately after receiving a stimulus. Positron emission tomography (PET) studies have shown that an increased need to gate information is accompanied by increased engagement of the thalamus. P50 wave testing is one of many auditory event-related potential studies.

Schizophrenia
A large interest in sensory gating research is directed at improving deficits among people diagnosed with Schizophrenia. People with schizophrenia often have deficits in gating the neuronal response of the P50 wave. Since people with schizophrenia can often have an overload of attended stimuli, the P50 wave may serve a critical role in illuminating sensory gating at a neurological level.

The P50 Auditory Gating deficit is one of the best established biological traits associated with schizophrenia.

Autism Disorders
Individuals diagnosed with Autism spectrum disorders (ASD) show patterns of restrictive and repetitive behaviors, reflecting a difficulty to inhibit excess sensory information in the brain. This information suggests sensory gating may be affecting some of the visible symptoms of ASD. Current research on this topic is limited.

Nicotine and sensory gating
One reason people report they like smoking cigarettes is nicotine's ability to aid their selective attention. In order to alleviate the stress of not being able to gate sensory input, nicotine can correct sensory gating deficits for individuals with Schizophrenia, but the effects only last about thirty minutes after nicotine intake. The same self-medication is present among those with attention-deficit/hyperactivity disorder.