Frequent lying and its biology is the subject of a fascinating article in Nature Neuroscience.
Scientists have shown that the brain’s fear and alarm circuitry (the amygdala) is usually triggered when one lies (even lies of omission or “white” lies). They’ve also shown that reducing this response by giving someone medications that affect the amygdala increases the likelihood that a person will lie.
But people who lie once have a somewhat smaller response to the next lie and this process of adaptation continues, seemingly indefinitely. They were also able to show that the reduction in response in the fear and alarm circuitry from one lie predicts the likelihood that in the next conversation a person will lie again. In other words the changes appear to be causal rather than just correlational.
They also found that this progressive increase in lying behavior occurred only for self-serving lies. The reduction in alarm response circuitry when lying didn’t have any effect on lying to help or protect others.
Garrett N, Lazzaro SC, Ariely D, Sharot T. The brain adapts to dishonesty. Nat
Neurosci. 2016 Dec;19(12):1727-1732. doi: 10.1038/nn.4426. PubMed PMID: 27775721;
PubMed Central PMCID: PMC5238933.