**Fentanyl self-administration and passive administration (1.5 mg/70 kg) have differential [https://scholar.googleusercontent.com/scholar.bib?q=info:Ct07MzeWBcsJ:scholar.google.com/&output=citation&scisdr=CiBKb9IEEIjgixEInRc:ACTRDVEAAAAAasUOhRdfe7UiiUuK6P0C3uTTzcQ&scisig=ACTRDVEAAAAAasUOhZZOppryrz-KHD6fwDheYes&scisf=4&ct=citation&cd=-1&hl=en EEG effects], including higher central-midline delta enhancement. | **Fentanyl self-administration and passive administration (1.5 mg/70 kg) have differential [https://scholar.googleusercontent.com/scholar.bib?q=info:Ct07MzeWBcsJ:scholar.google.com/&output=citation&scisdr=CiBKb9IEEIjgixEInRc:ACTRDVEAAAAAasUOhRdfe7UiiUuK6P0C3uTTzcQ&scisig=ACTRDVEAAAAAasUOhZZOppryrz-KHD6fwDheYes&scisf=4&ct=citation&cd=-1&hl=en EEG effects], including higher central-midline delta enhancement. |