“The man of genius, whether as artist or thinker, requires a mass of accidental variations to select from a rigidly selective process of attention” ~Boris Sidi
THE GIFT OF SELECTIVE ATTENTION
Selective attention is a process where an individual focuses on one specific stimulus in his/her environment while blocking information that comes through other sensory modalities. A perfect example to understand this type of attention is a party setup. We expect a lot of noise and sounds of other people conversing with each other. But we still can attend to one person at a time without being distracted by what is going on around us. In this way, selective attention becomes an advantageous cognitive control mechanism.
We can speculate about the evolutionary benefit that this particular ability gave in the past that eventually led to its integration. A mutation that was helpful in the development of selective attention helped the early man focus only on the relevant aspects/stimuli in his environment and ignore other unnecessary information. It also helps prevent the cortical regions from being flooded by insignificant details. For example, it enabled man to focus on the sound of a deer (a potential source of food for him) and follow it to eventually find food and ignore the screeching sound of birds in the background at the same time. Hence through, the process of increasing the ease of finding food, it increased human survival.
This crucial role of selective attention is facilitated through the existence of the sensory gating system. A research study conducted by Grunwald and others indicates that sensory gating can be a multistep process that starts with the temporoparietal cortex and prefrontal cortex. Further, the process is taken up by the hippocampus.
ELUCIDATING THE PROCESS
As sensory data flows into the thalamus, the place where most sensory information enters the brain, the prefrontal cortex selectively suppresses it. Without traveling through the thalamus, no sensory information can reach the cerebral cortex. Sensory gating is a process through which irrelevant stimuli are isolated from meaningful ones. And it may explain both sensory overload and the cognitive abnormalities that are exhibited in schizophrenia patients. Modulation of sensation and perception as a result of arousal shifts, recent stimulus exposure, and selective attention are all examples of sensory gating.
Leaky sensory processing, or a diminished ability to screen or block stimuli from conscious awareness, was linked to real-world creative accomplishment. According to the findings, creative people with “leaky” sensory gating are more likely to deploy attention across a broader focus or a wider variety of stimuli.
Sensory gating is a crucial mechanism for sleep regulation. Sensory information is processed at a subcortical level during sleep and awakeness in animals as the thalamus is assumed to gate sensory input. Such processes would safeguard sleep continuity by filtering out tiny noises before they reach the cortex and disrupt sleep. If the thalamus’ gate is closed, the cortex simply turns out the world and goes to sleep.
MEASUREMENT OF SENSORY GATING
Sensory gating can be measured in an easy way. Subjecting a participant to 2 identical sounds with a very minimal gap between them (500ms approx) and giving a gap of a few seconds before exposure to another pair of the same information. When the first stimulus generates potentials in the neural circuits of the brain, its nature is registered. When another stimulus just after that enters the brain, it is actively inhibited from reverberating in our circuits as it has no difference with the nature of the first stimulus.
One study conducted upon rats tried to understand the differential activity of the interneurons present in the hippocampus and the pyramidal neurons. Upon presenting the pattern of sounds through a gap of 500 ms between the pairs, they found that the interneurons were much more efficient in inhibiting the identical sounds. This research conclusion points out, full-text specialization in the organic level, i.e., in the neurons for executing sensory gating.
THE DISTORTION IN SCHIZOPHRENICS
Impaired sensory gating, defined as a diminished ability to block the processing of irrelevant and uninformative sensory data, is a significant cognitive symptom in people with schizophrenia.
Prepulse inhibition (PPI) is a neuropsychological phenomenon in which the motor response to a startling stimulus (pulse) is dramatically diminished when that stimulus is preceded by a typically weaker input (prepulse). P50, an electroencephalographic event-related potential wave produced 50 milliseconds after exposure to an auditory stimulus, is used to assess sensory gating. PPI has also been quantified using the eyeblink response measured by electromyography of the orbicularis oculi muscle, which has strong genetic and biological connections.
P50 wave inhibition hinders schizophrenia patients from filtering out irrelevant auditory stimulation, allowing auditory hallucinations and delusional interpretations to form more easily. Nicotine enhances sensory gating and prepulse inhibition in schizophrenia patients while reducing some severe psychiatric symptoms. Another factor to consider is that sensory gating is absent in first-degree relatives who have not yet developed psychopathology.
Research by RJ Thoma and others tried to compare the cortical thickness of auditory cortical areas responsible for sensory gating between normal and schizophrenic patients with the help of 3D sMRI. They found that people with schizophrenia showed thinner cortical thickness in auditory regions of both right and left hemispheres in comparison to non-schizophrenic.
OTHER SPECIAL CASES
The Sensory Gating Inventory (SGI), a validated instrument, revealed that adults with ADHD had considerably higher values. P50 suppression was much lower in adults with ADHD than in healthy participants.
Research conducted by Jessen and others shows that patients suffering from Alzheimer’s disease show a disruption in their sensory gating capacities. They speculate that this weakening of capacity could be due to dysfunction of the alpha-7 subunit in the cholinergic-nicotinic receptor that is seen in the pathology.
When a threat enters working memory, anxious people are less effective at gating danger access. Even when the threat is unrelated to the activity at hand, people with a high disposition for anxiety store a lot of information in their working memory.
Induced negative emotion has been shown to reduce respiratory sensory gating function in healthy persons. In conclusion, findings imply that in healthy people with low-moderate anxiety levels, a positive emotional context is associated with superior brain inhibitory systems that filter out recurrent respiratory impulses.
HOW DO MOTIVATIONAL STATES IMPACT?
Researchers have tried to understand the impact of different motivational states on sensory gating. One study has found that sensory gating gets strengthened when an acute stressor is given to rats in the form of saline injections. They observed an increased response to the primary stimulus and a much more decrease in response to the second identical stimulus in the pair. The study also found out that inhibitory gating weakened in rats that were subjected to long-term food deprivation. Finally, an interesting research conclusion indicated that sensory gating increase is strengthened during the process of searching.
THE NEUROTRANSMITTER BASIS
Research also shows that improved sensory gating ability positively correlates with behavioral inhibition. This is facilitated by increased levels of GABA neurotransmitter concentrations. This might possibly explain how sensory gating can support one’s working memory and attention to what is relevant and preferred. This could also help us understand how increased GABA levels reduce/inhibit the urge to act upon irrelevant information behaviorally in the environment.
CONCLUSION
Sensory gating plays a crucial role in maintaining human life. Through its ability to highlight the important details and blot out the unimportant ones, it has brought about a balance amidst chaos in every mind. Without this system, we would have experienced an immense overload of our sensory and processing systems, which would have placed a hefty demand upon our brains. But luckily, mutation and natural selection favored the development of this sophisticated gating system, whose complete basis and function are yet to be discovered by the scientific community.
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