Cognitive functions of adolescent childhood cancer survivors assessed by event-related potentials

Neurophysiological methods were applied to examine subtle central nervous system (CNS) adverse effects for adolescent childhood cancer survivors. We analyzed auditory event-related potentials (ERPs)-P300 and MMN/P3a complex-to find out whether there was impaired attention orientation in asymptomatic cancer survivors, and whether these ERP methods could be used as more objective tools in detecting those survivors who might need academic testing. Previous clinical studies of P300 have focused on leukemia survivors. MMN for cancer survivors has not been reported.

The subjects were survivors of childhood leukemia (n=11) and solid tumors (n=8), as well as healthy controls (n=10). The mean age was 15.5 years for survivors and 15.9 years for controls. Pure sine-wave tones (500 and 553 Hz, 100 ms) were used as stimuli in an oddball paradigm. The ERPs to frequency change were measured. MMN recordings were performed in a passive non-attended situation where the subject was watching a voiceless video cartoon. P300 was produced thereafter, but in an active attend situation, by the same auditory oddball paradigm as MMN.

A significant difference was detected between the groups for the latency of P300 at electrodes Cz (P = 0.03) and C4 (P = 0.05). The cancer survivors had prolonged P300 latencies as an indication of prolonged short-term memory processing. The area and latency parameters of MMN did not differ significantly between the study groups, but in cancer survivors, the area and the mean amplitude of the subsequent P3a wave were diminished. The results indicate that the discrimination process was not as easy for the survivors as for the controls. However, it seems that in cancer survivors the basic mechanism starting attention shift to novel stimuli is not impaired.

These results indicate that it is important to carefully evaluate the proper methods for the teaching of children who are survivors of malignancies. The auditory information may not always lead to the best possible learning results.