title: The gamma band effect for episodic memory encoding is absent in epileptogenic hippocampi.
abstract: OBJECTIVE
  The analysis of hippocampal local field potentials in humans during the encoding of episodic memories has revealed that a robust increase in gamma band oscillatory power predicts successful item encoding, termed the gamma band subsequent memory effect (SME). No previous investigation has looked for differences in this pattern between epileptogenic and non-epileptogenic sources; we sought to examine the gamma band effect in seizure patients to address this question.
  
  
  METHODS
  We recorded hippocampal activity in nine patients who underwent stereoelectroencephalography for seizure localization and also performed the Free Recall task, a standard test of episodic memory. We compared gamma band oscillatory activity between 15 electrodes localized to epileptogenic hippocampi and 24 electrodes in non-epileptogenic hippocampi.
  
  
  RESULTS
  The epileptogenic hippocampi exhibited a significant decrease in gamma band power during successful item encoding, whereas the non-epileptogenic group exhibited the expected positive gamma band effect (t(37)=4.69, p<0.0001).
  
  
  CONCLUSIONS
  The typical gamma band effect is reversed for epileptogenic hippocampi.
  
  
  CONCLUSIONS
  This is the first study to demonstrate a difference for epileptogenic hippocampi for an important oscillatory pattern that normally predicts successful item encoding. Patients with epilepsy suffer selective impairment of episodic memory ability, so our findings are especially relevant for clinicians and memory researchers alike.
authors.affiliation: Neurological Surgery, University of Texas-Southwestern, Dallas, TX 75390, USA.
authors.forename: Bradley
authors.initials: B
authors.lastname: Lega
authors.affiliation: Epileptology, The Cleveland Clinic Epilepsy Institute, Cleveland, OH 44195, USA.
authors.forename: Sasha
authors.initials: S
authors.lastname: Dionisio
authors.affiliation: Epilepsy Surgery, The Cleveland Clinic Epilepsy Institute, Cleveland, OH 44195, USA.
authors.forename: William
authors.initials: W
authors.lastname: Bingaman
authors.affiliation: Epileptology, The Cleveland Clinic Epilepsy Institute, Cleveland, OH 44195, USA.
authors.forename: Imad
authors.initials: I
authors.lastname: Najm
authors.affiliation: Epilepsy Surgery, The Cleveland Clinic Epilepsy Institute, Cleveland, OH 44195, USA. Electronic address: gonzalj1@ccf.org.
authors.forename: Jorge
authors.initials: J
authors.lastname: Gonzalez-Martinez
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004567:Electrodes, Implanted; D004827:Epilepsy / Q000175:diagnosis* / Q000503:physiopathology*; D005260:Female; D065818:Gamma Rhythm / Q000502:physiology*; D006624:Hippocampus / Q000503:physiopathology*; D006801:Humans; D008297:Male; D061212:Memory, Episodic; D011939:Mental Recall / Q000502:physiology; D008875:Middle Aged; D055815:Young Adult
keywords: Epilepsy; Episodic memory; Gamma oscillations; Hippocampus; Subsequent memory effect