The effects of chronicity on burst structure in epileptogenic foci

Pyramidal tract neurons (PTNs) from tungstic acid, cobalt and alumina gel foci in cat were studied for spontaneous and antidromically-evoked firing patterns. Specifically, the structured long-first-interval (LFI) burst was looked for. The LFI burst did occur spontaneously from PTNs in tungstic acid foci but could not be antidromically evoked. The LFI burst did not occur as often as would have bee predicted from cobalt and alumina foci, but, in foci older than 60 days, antidromically-evoked activity could be a burst which was structurally identical to those which occurred spontaneously. This data, in addition to that from acute penicillin foci, would indicate that the ability for single antidromic APs to evoke burst activity in PTNs is a function of the chronicity of the epileptic focus rather than the agent used to produce the focus.