Evidence on the periodic mechanism in herpes simplex encephalitis.

A case of herpes simplex encephalitis is described in which the EEG was recorded 5 times between the 5th day of illness and death on the 13th day. Repetitive discharges occurred at intervals of 3.5 or 2 sec; at first they were larger and earlier on the right side, finally on the left; on day 11 they could be earlier on either side and sometimes ceased briefly on either side. They were associated with jerks. It is argued that this periodicity cannot be explained by cortical isolation or a single pacemaker and hence favours a third possibility, a more or less diffuse disturbance of the time constant of excitability at the cellular level.