Authors' reply

The findings reported by Kruesi et al are intriguing. We showed that adult pathological liars had 22% more prefrontal white matter than normal controls and 26% more than antisocial controls. Based on mean values reported by Kruesi et al, they too found higher prefrontal white matter/whole brain volumes in adolescent liars compared with both normal controls (14.7%) and antisocial controls (50%). Their sample of adolescent liars was small (n=4) and therefore underpowered for the detection of a true increase in prefrontal white matter. We therefore believe that the results of Kruesi et al support our findings rather than refute them. With a larger sample size they may well have found a statistically significant increase in prefrontal white matter in liars. An important difference between the two studies is that the mean age of our adult pathological liars (36.5 years) was more than twice that of the adolescent liars (15.9 years). Since prefrontal white matter may not be fully developed until 30 years of age (Paus et al, 2001), there may be insufficient development of prefrontal white matter in adolescents to facilitate pathological lying. Taken together the findings suggest a neurodevelopmental hypothesis whereby individual differences in white matter predispose more to lying in adulthood when neurodevelopment is complete.

A further difference between the studies is that although our pathological liars were matched with controls for IQ, the control group of Kruesi et al had a 31 point higher IQ than the liars, which may affect their findings. A further important difference is that we assessed pathological lying in adults, whereas Kruesi et al appear to be assessing excessive lying in adolescents. There may be a continuum of lying from normative lying (controls) to excessive lying (the adolescents of Kruesi et al) to pathological lying (our adults). Whether prefrontal white matter (or any other brain structure) is related in a neurodevelopmental context to this lying continuum remains to be determined.