Investigating the role of the hippocampus in the implicit and explicit expression of statistical learning in patients with temporal lobe epilepsy

Statistical learning (SL) has been proposed to depend on the hippocampus, but traditional neuropsychological theories of long-term memory posit that the hippocampus is only necessary for explicit memory processes, not implicit memory processes. To reconcile these two accounts, we exposed 27 temporal lobe epilepsy (TLE) patients to a continuous speech stream containing embedded trisyllabic words, then tested their statistical knowledge using both implicit and explicit behavioural measures. TLE patients showed impairments on two explicit measures of SL alongside intact performance on an implicit measure of SL. These results suggest that the hippocampus may only be necessary for the explicit expression, but not the initial acquisition or implicit expression, of statistical knowledge.