Subsequent memory effect in intracranial and scalp EEG

• Published in: NeuroImage (Orlando, Fla.) Vol. 84; pp. 488 - 494
• Main Authors: Long, Nicole M., Burke, John F., Kahana, Michael J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.01.2014; Elsevier; Elsevier Limited
• Subjects: Adolescent; Algorithms; Biological and medical sciences; Brain; Brain - physiology; Brain Mapping - methods; Data processing; EEG; Electrodes; Electroencephalography; Electroencephalography - methods; Epilepsy - diagnosis; Epilepsy - physiopathology; Free-recall; Fundamental and applied biological sciences. Psychology; Humans; iEEG; Internationality; Memory; Memory, Long-Term - physiology; Mental Recall - physiology; Nerve Net - physiopathology; Patients; Reproducibility of Results; Scalp; Sensitivity and Specificity; Vertebrates: nervous system and sense organs; Young Adult; Free-recall; EEG; Memory; iEEG; Electrophysiology; Electroencephalography
• ISSN: 1053-8119; 1095-9572; 1095-9572
• DOI: 10.1016/j.neuroimage.2013.08.052

Successful memory encoding is marked by increases in 30–100Hz gamma-band activity in a broad network of brain regions. Activity in the 3–8Hz theta band has also been shown to modulate memory encoding, but this effect has been found to vary in direction across studies. Because of the diversity in memory tasks, and in recording and data-analytic methods, our knowledge of the theta frequency modulations remains limited. The difference in the directionality of these theta effects could arise from a distinction between global cortical and deeper subcortical effects. To address this issue, we examined the spectral correlates of successful memory encoding using intracranial EEG recordings in neurosurgical patients and scalp EEG recordings in healthy controls. We found significant theta (3–8Hz) power modulations (both increases and decreases) and high gamma (44–100Hz) power increases in both samples of participants. These results suggest that (1) there are two separate theta mechanisms supporting memory success, a broad theta decrease present across both the cortex and hippocampus as well as a theta power increase in the frontal cortex, (2) scalp EEG is capable of resolving high frequency gamma activity, and (3) iEEG theta effects are likely not the result of epileptic pathology. •Spectral correlates of memory encoding in 93 intracranial and 102 scalp EEG subjects•Memory encoding is supported by frontal theta increases and broad theta decreases.•Scalp EEG is capable of resolving high gamma (30–100Hz) activity.•Theta effects in intracranial EEG are likely not the result of epileptic slowing.