Neural circuit
The neural circuit was a section of the Human brain related to ESP ability.

In 2265, when the starship  encountered the galactic barrier, nine crewmen whose esper rating had been rated as above average were killed due to damage to their neural circuits. ()

In 2268, Leonard McCoy claimed that the Kelvans' paralysis field was a sufficient hold over the Enterprise crew, as "they [could] jam all [their] neural circuits" with it. ()

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Biology