Right hippocampal pathology inhibits the Flynn effect in temporal lobe epilepsy

If brain pathology impedes the mechanisms that drive the Flynn effect, the gap between the mean IQ of patient groups and the general population will increase over successive generations. We examined the IQs of a large series of patients aged between 18 and 35 years, with homogenous underlying brain pathology tested over two decades, for evidence of a Flynn effect; 381 patients with temporal lobe epilepsy and unilateral hippocampal sclerosis (n = 221 left hippocampal sclerosis, LHS; n = 160 right hippocampal sclerosis, RHS) completed the Wechsler Adult Intelligence Scales. Patients assessed between 1990 and 2000 were assessed on the Wechsler Adult Intelligence Scale-Revised (WAIS-R; n = 234). Patients assessed between 2001 and 2011 were assessed on the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III; n = 147). The IQ scores were adjusted for the progressive obsolescence of norms using the following equation: adjusted IQ = recorded IQ - (estimated magnitude of Flynn effect in the normal population x years since test was normed, at the time of assessment). In the RHS group there was a significant negative correlation between the year of assessment and the adjusted Verbal IQ (r = -.18, p < .05) and adjusted Performance IQ (r = -.20, p < .01). There were no significant correlations between the adjusted IQ scores and the year of assessment in the LHS group. Our data suggest that the gap between the mean IQ in the general population and that in patients with right hippocampal pathology is widening in successive generations. The findings are discussed in relation to the current theories regarding the mechanisms that drive the Flynn effect.