Objectives: To study the involvement of the hippocampus in the P50 evoked potential generation and of its suppression in epileptic patients with left or right unilateral hippocampal excision. Methods: A transverse study with control group for comparison was done. Exclusion criteria were another neurological or psychiatric disease, deafness, family history of psichosis, use of any atypical antipsychotic medication or use of drugs of abuse in the last month. The population was divided in two groups: group 1 (n = 34) - hippocampal excision; group 2 (n = 40) - normal controls. All participants were submitted to P50 recordings. Critical variables for the analysis included conditioning (S1) and test (S2) P50 amplitude and S2/S1 ratio. T-test was used to compare the mean values between the groups and chis-quare test was done to compare S2/S1 suppression frequency. Results: The mean S2/S1 ratio was 0.74 ± 0.44 in the group 1 and 0.42 ± 0.24 in the group 4 (p < 0.001). After comparing amplitude mean values, it has been found that S2 amplitude was significantly smaller in the control group (p < 0.001). Conclusions: This study suggests that the hippocampus is not the generator of the waves in the P50 mid-latency auditory evoked potentials. This structure, however, is most likely involved in the generation of the suppression of the S2 testing wave in the double click paradigm.
P50 auditory evoked potential; generators; epilepsy; hippocampus; amigdala-hippocampectomy