Abstract
Auditory beats are amplitude-modulated signals (monaural beats) or signals that subjectively cause the perception of an amplitude modulation (binaural beats). We investigated the effects of monaural and binaural 5 Hz beat stimulation on neural activity and memory performance in neurosurgical patients performing an associative recognition task. Previously, we had reported that these beat stimulation conditions modulated memory performance in opposite directions. Here, we analyzed data from a patient subgroup, in which microwires were implanted in the amygdala, hippocampus, entorhinal cortex and parahippocampal cortex. We identified neurons responding with firing rate changes to binaural versus monaural 5 Hz beat stimulation. In these neurons, we correlated the differences in firing rates for binaural versus monaural beats to the memory-related differences for remembered versus forgotten items and associations. In the left hemisphere, we detected statistically significant negative correlations between firing rate differences for binaural versus monaural beats and remembered versus forgotten items/associations. Importantly, such negative correlations were also observed between beat stimulation-related firing rate differences in the pre-stimulus window and memory-related firing rate differences in the post-stimulus windows. In line with concepts of homeostatic plasticity, our findings suggest that beat stimulation is linked to memory performance via shifting baseline firing levels.
Highlights
Introduction published maps and institutional affilAuditory beat stimulation is a non-invasive brain stimulation technique, for which effects on anxiety and cognition including memory have been reported
An impact of beat stimulation on memory performance has been described by several groups
We have reported that binaural and monaural 5 Hz beat stimulation modulated memory performance in opposite directions based on data from a larger patient group [5]
Summary
Introduction published maps and institutional affilAuditory beat stimulation is a non-invasive brain stimulation technique, for which effects on anxiety and cognition including memory have been reported (for overviews, see, e.g., [1,2]). Auditory beats are amplitude-modulated tones with modulation frequencies in the range of typical electroencephalographic (EEG) rhythms. Beat stimulation is either applied by presenting amplitude-modulated beat signals to one ear or both ears (monaural beats), or by presenting the original sine waves separately to each ear (binaural beats). In this latter, more frequently investigated case, beat perception results from the responses of phase-sensitive brain stem neurons of the superior olivary complex [3]. It has been shown that monaural and binaural beats have a different impact on EEG power, phase patterns and phase synchronization (e.g., [4,5,6]). Phase synchronization and other phase-related mechanisms play an important role in long-term iations
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