Abstract
Recent research has revealed that neural oscillations in the theta (4–8 Hz) and alpha (9–14 Hz) bands are predictive of future success in memory encoding. Because these signals occur before the presentation of an upcoming stimulus, they are considered stimulus-independent in that they correlate with enhanced memory encoding independent of the item being encoded. Thus, such stimulus-independent activity has important implications for the neural mechanisms underlying episodic memory as well as the development of cognitive neural prosthetics. Here, we developed a brain computer interface (BCI) to test the ability of such pre-stimulus activity to modulate subsequent memory encoding. We recorded intracranial electroencephalography (iEEG) in neurosurgical patients as they performed a free recall memory task, and detected iEEG theta and alpha oscillations that correlated with optimal memory encoding. We then used these detected oscillatory changes to trigger the presentation of items in the free recall task. We found that item presentation contingent upon the presence of pre-stimulus theta and alpha oscillations modulated memory performance in more sessions than expected by chance. Our results suggest that an electrophysiological signal may be causally linked to a specific behavioral condition, and contingent stimulus presentation has the potential to modulate human memory encoding.
Highlights
In the laboratory setting, episodic memory is commonly studied by presenting participants with a list of items and asking them to later recall those items
Data from electroencephalography (EEG) (Klimesch et al, 1997), magnetoencephalography (Osipova et al, 2006), and electrocorticography (ECoG) (Fell et al, 2001; Sederberg et al, 2007) have revealed that changes in theta (4–8 Hz) and alpha (10–14 Hz) oscillations correlate with successful episodic memory encoding and retrieval
The participants agreed to run in two different tasks: a standard version of free recall followed by an oscillatory contingent, or brain computer interface (BCI), version
Summary
Episodic memory is commonly studied by presenting participants with a list of items and asking them to later recall those items. The ability to record electrophysiological data from participants engaging in a memory task has begun to reveal the neural correlates of these behavioral phenomena. While important electrophysiological hallmarks of encoding and retrieval are evident in the time domain (Rugg and Wilding, 2000), many lines of evidence have suggested that neural oscillations have a unique functional role in the memory system (Basar et al, 1999; Kahana, 2006; Nyhus and Curran, 2010). Data from electroencephalography (EEG) (Klimesch et al, 1997), magnetoencephalography (Osipova et al, 2006), and electrocorticography (ECoG) (Fell et al, 2001; Sederberg et al, 2007) have revealed that changes in theta (4–8 Hz) and alpha (10–14 Hz) oscillations correlate with successful episodic memory encoding and retrieval. Studies using transcranial magnetic stimulation have suggested that such alpha activity synchronizates across large regions of cortex during memory processing (Zanto et al, 2011)
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