Recovery cycle of the cerebral neocortex: preliminary observations in epileptic patients

The recovery cycle of the amplitude of the potential evoked in the cerebral neocortex by paired electrical stimuli of the underlying white matter was studied in 5 epileptic patients with intracerebral electrodes chronically implanted stereotactically. A reproducible pattern was apparent for the late components of the potential (i.e., the peak-to-peak amplitude between the second and the third peak, with an average peak latency of 14 and 35 ms, respectively). There was an early period of facilitation (5-10 ms interstimulus interval) followed by a period of relative or absolute depression (20-100 ms) with recovery at an interstimulus interval of about 150 ms. The recovery function of the early components of the potential (i.e., the peak-to-peak amplitude between the first and the second peak, with an average peak latency of 6 and 14 ms, respectively) was variable; recovery was reached at about 150 ms. The responsiveness seemed less in the most epileptogenic cortical areas.