Delayed signal EEG trigger

Long EEG recordings are often necessary to capture the signals in the short period just before an epileptic attack. This procedure has many disadvantages. The equipment described below enables only the signals of interest to be recorded. It is designed to operate in conjunction with a commercial electroencephalograph and consists of a signal store with a programmable series of logic gates for sensing the onset of an epileptic discharge and activating the chart recorder. The particular system described has a signal bandwidth of d.c. to 25 Hz in all 16 channels, and, because of their particular clinical diagnostic importance, all signals for the 20 seconds immediately preceding the discharge are recorded. The recording can take place for up to one hour after the attack and, if a second attack should occur, it can also be recorded similarly to the first one.