Abstract

Objective: To clarify whether long time constant is useful for detecting the after-slow activity of epileptiform discharges : sharp waves and spikes and for differentiating EDs from sharp transients.Methods: We employed 68 after-slow activities preceded by 32 EDs and 36 Sts from 52 patients with partial and generalized epilepsy defined by visual inspection. High-frequency activity associated with the apical component of EDs and Sts was also investigated to endorse two groups. After separating nine Sts that were labeled by visual inspection but did not fulfill the amplitude criteria for after-slow of Sts, 59 activities were analyzed about the total area of after-slow under three TCs.Results: Compared to Sts, HFA was found significantly more with the apical component of EDs. The total area of after-slow in all 32 EDs under TC 2 s was significantly larger than those under TC 0.3 s and 0.1 s. Conversely, no significant differences were observed in the same parameter of 27 Sts among the three different TCs. Regarding separated nine Sts, the total area of after-slow showed a similar tendency to that of 27 Sts under three different TCs.Significance: These results suggest that long TC could be useful for selectively endorsing after-slow of EDs and differentiating EDs from Sts. These findings are concordant with the results of the HFA analysis. Visual inspection is also equally good as the total area of after-slow analysis.