Heroin abusers' performance on the Tower of London Test relates to the baseline EEG alpha2 mean frequency shifts

Abstract

Planning function deficit is the most consistent finding in neuropsychological studies of heroin addicts. The performance on the Tower of London Test (TLT) correlated with the duration of daily heroin abuse (DDHA) in our previous study. Alpha2 mean frequency in anterior/central derivations was also predicted by DDHA in the same patient population. This retrospective study was undertaken in order to understand better the relationships between observed neurological deviations in heroin abusers. Thirty-three heroin addicts and 12 healthy males were evaluated with 14 neuropsychological tests and resting eyes-closed electroencephalography (EEG). Multivariate tests showed that performance on the difficult (five-move) problems of TLT was strongly predicted by the EEG alpha2 mean frequency shifts, and these relationships were generally mediated by chronic heroin length. However, post-hoc analyses at separate leads demonstrated that the relationships between cognitive variables and alpha2 mean frequencies in the left hemisphere were independent of chronic heroin effects, whereas elevation of alpha2 frequency in the right hemisphere was strongly predicted by chronic heroin intake length. The patients with extremely high alpha2 mean frequency at the left central region were especially prone to failure in TLT due to the inability of the hypothesized alpha2-generating network, which normally projects to the central and temporal derivations bilaterally and to the right posterior temporal derivation to function appropriately. Hence, it was concluded that planning dysfunction in heroin abusers is related to alpha2 mean frequency shifts predominantly at the central regions.