To evaluate the neurophysiological differences between panic disorder (PD) and generalized anxiety disorder (GAD), 52 patients with PD and 34 with GAD were investigated using event-related potentials (ERP). The ERP were recorded using a tone discrimination task, and peak latencies for N1, P2, N2, and P3 at a Pz electrode site were measured. In addition to analyzing the peak latencies of the ERP, the interpeak latencies (IPL; N1-P2, P2-N2, and N2-P3) were also analyzed. The same analysis was performed in 28 age-matched healthy volunteers (controls). When compared to those of the GAD and control groups, the mean latencies of P2, N2, and P3 were shorter in the PD patients. With regard to the IPL in the PD patients, the N1-P2 IPL was shorter than that in the other groups, and no individual with PD had a longer N1-P2 IPL than 1 SD above the mean of the controls. These findings suggest that certain attention-related processes in the cerebrum that affect ERP data are accelerated in PD patients. These findings demonstrate that it may be useful to neurophysiologically distinguish PD from GAD by measuring ERP peak latencies and IPL.

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Most studies on event-related potentials (ERP) in psychiatric illness or dementia have focused on the single-peak latency of ERP components. In the present study, not only peak latencies of ERP components (N1, P2, N2, and P3) but also interpeak latencies (IPL; N1-P2, P2-N2, and N2-P3) were analyzed using the auditory oddball task. Thirty-five senile depressed patients and 34 patients with dementia of the Alzheimer type (DAT) were compared to 39 age-matched healthy volunteers. The mean latencies of P2 and P3 were shorter in patients with senile depression than in controls. In DAT patients, the N2 and P3 latencies were longer. When the IPL was assessed, however, only the mean IPL of N1-P2 was shorter in patients with senile depression, while the P2-N2 IPL were longer in those with DAT. The IPL results suggest that in senile depression the early cognitive process is hastened and in DAT the middle process is disturbed. Based on these results, we conclude that IPL of the auditory ERP might be used to reveal the disturbed steps within the cognitive process.

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