Expected reward modulates encoding-related theta activity before an event

• Published in: NeuroImage (Orlando, Fla.) Fla.), 2013-01, Vol.64 (6), p.68-74
• Main Authors: Gruber, Matthias J., Watrous, Andrew J., Ekstrom, Arne D., Ranganath, Charan, Otten, Leun J.
• Format: Article
• Language: English
• Subjects: Adult; Anticipation; Anticipation, Psychological - physiology; Biological and medical sciences; Brain research; Electrodes; Electroencephalography; Electroencephalography - methods; Experiments; Female; Fundamental and applied biological sciences. Psychology; Humans; Long-term memory; Male; Memory - physiology; Memory encoding; Motivation - physiology; Neuronal Plasticity - physiology; Prestimulus activity; Reward; Studies; Theta; Theta Rhythm - physiology; Vertebrates: nervous system and sense organs; Young Adult
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2012.07.064

Oscillatory brain activity in the theta frequency range (4–8Hz) before the onset of an event has been shown to affect the likelihood of successfully encoding the event into memory. Recent work has also indicated that frontal theta activity might be modulated by reward, but it is not clear how reward expectancy, anticipatory theta activity, and memory formation might be related. Here, we used scalp electroencephalography (EEG) to assess the relationship between these factors. EEG was recorded from healthy adults while they memorized a series of words. Each word was preceded by a cue that indicated whether a high or low monetary reward would be earned if the word was successfully remembered in a later recognition test. Frontal theta power between the presentation of the reward cue and the onset of a word was predictive of later memory for the word, but only in the high reward condition. No theta differences were observed before word onset following low reward cues. The magnitude of prestimulus encoding-related theta activity in the high reward condition was correlated with the number of high reward words that were later confidently recognized. These findings provide strong evidence for a link between reward expectancy, theta activity, and memory encoding. Theta activity before event onset seems to be especially important for the encoding of motivationally significant stimuli. One possibility is that dopaminergic activity during reward anticipation mediates frontal theta activity related to memory. ► Prestimulus theta activity predicts subsequent memory formation. ► Theta activity is also sensitive to reward expectancy. ► Is there a relationship between theta, expected reward, and memory formation? ► Prestimulus theta only predicted later memory performance for high reward trials. ► Prestimulus theta seems crucial for encoding of motivationally significant stimuli.