Participants sat in a comfortable chair with neck support in a darkened room and were instructed to close their eyes and relax as completely as possible. EEG data were collected continuously for 5 min. Data were collected over the course of more than 20 years using two different systems. For participants in the MTFS older and younger cohorts (71% of the sample), EEG was recorded via Grass Neurodata 12 systems (128-Hz sampling rate, passband from 1 to 30 Hz with a rolloff of 6 dB). Hardware constraints limited the number of signals recorded. EEG was recorded from the bipolar derivations O1–P7 and O2–P8 and from Cz referenced to linked earlobes. Eye blinks and other eye movements were recorded by means of a transverse electrode arrangement, with one superior to the eye and one on the outer canthus. For participants in the ES sample (with the exception of 14 subjects), a Biosemi ActiveTwo system was used to collect continuously recorded EEG data with a sampling rate of 1024 Hz. ActiveTwo amplifiers are DC-coupled, and signals were lowpass-filtered using a digital 5th-order Bessel anti-aliasing sinc filter with a cutoff frequency (3-dB attenuation) of 205 Hz. ActiveTwo signals are monopolar.
