Modulating Human Memory via Entrainment of Brain Oscillations

Brain oscillations in various frequency bands have been linked to memory processes. Oscillatory entrainment refers to the modulation of neural oscillations that in the human brain can be achieved via three rhythmic stimulation approaches: sensory stimulation, noninvasive electric/magnetic stimulation, and invasive electrical stimulation. Studies using different techniques of entrainment lend support to the idea that brain oscillations can modulate human memory, and suggest that oscillations are causally relevant for memory processes In the human brain, oscillations occur during neural processes that are relevant for memory. This has been demonstrated by a plethora of studies relating memory processes to specific oscillatory signatures. Several recent studies have gone beyond such correlative approaches and provided evidence supporting the idea that modulating oscillations via frequency-specific entrainment can alter memory functions. Such causal evidence is important because it allows distinguishing mechanisms directly related to memory from mere epiphenomenal oscillatory signatures of memory. This review provides an overview of stimulation studies using different approaches to entrain brain oscillations for modulating human memory. We argue that these studies demonstrate a causal link between brain oscillations and memory, speaking against an epiphenomenal perspective of brain oscillations. In the human brain, oscillations occur during neural processes that are relevant for memory. This has been demonstrated by a plethora of studies relating memory processes to specific oscillatory signatures. Several recent studies have gone beyond such correlative approaches and provided evidence supporting the idea that modulating oscillations via frequency-specific entrainment can alter memory functions. Such causal evidence is important because it allows distinguishing mechanisms directly related to memory from mere epiphenomenal oscillatory signatures of memory. This review provides an overview of stimulation studies using different approaches to entrain brain oscillations for modulating human memory. We argue that these studies demonstrate a causal link between brain oscillations and memory, speaking against an epiphenomenal perspective of brain oscillations. the rhythmic activity of a population of neurons within a given frequency band. Brain oscillations can be measured at different spatial scales ranging from below a millimeter in case of local field potentials to about 1 cm for intracranial electroencephalography (iEEG), 1–2 cm for magnetencephalography (MEG), and several centimeters in the case of EEG. two variables x and y are causally related if a manipulation of x (e.g., oscillations) causes a change in y (e.g., memory). '[…] is the process whereby two interacting oscillating systems, which have different periods when they function independently, assume a common period.' (https://en.wikipedia.org/wiki/Injection_locking#Entrainment). In neuroscience, the two oscillating systems are (i) a rhythmic stimulator (i.e., flickering stimulus, electrical pulses, current sine wave, etc.) and (ii) the stimulated neural population. a narrow band neural response to entrainment which is phase-locked to the entraining stimulus and outlasts stimulation by at least two oscillatory cycles (Box 1). memory for specific experiences, often from an autobiographical perspective, in which the time, place, and other contextual information can be explicitly stated or internally conjured. the process by which information is maintained and manipulated across a short time-interval (typically a few seconds). WM has a limited capacity of only a few items but allows their direct access.