Synchronizing Brain Rhythms to Improve Cognition

Abstract

Impaired cognition is common in many neuropsychiatric disorders and severely compromises quality of life. Synchronous electrophysiological rhythms represent a core mechanism for sculpting communication dynamics among large-scale brain networks that underpin cognition and its breakdown in neuropsychiatric disorders. Here, we review an emerging neuromodulation technology called transcranial alternating current stimulation that has shown remarkable early results in rapidly improving various domains of human cognition by modulating properties of rhythmic network synchronization. Future noninvasive neuromodulation research holds promise for potentially rescuing network activity patterns and improving cognition, setting groundwork for the development of drug-free, circuit-based therapeutics for people with cognitive brain disorders.

Keywords: cognition; cognitive deficits; cross-frequency coupling; neuropsychiatric disorders; synchronization; transcranial alternating current stimulation.

Figure 1

(a) Asynchronous rhythmic activity in the brain during cognition. Left: The blue and magenta signals reflect rhythmic activity from the corresponding cortical regions. Weak interregional phase synchronization manifests as inconsistent relative phases between the two signals over time, evident in the different phases at which one signal reaches its peak relative to the other signal. Right: During cross-frequency phase-amplitude coupling (PAC), the amplitude of a high-frequency rhythm is phase-locked to the phase of a low-frequency rhythm. In this example, the magenta signal from the corresponding cortical region shows high-frequency activity that is only weakly phase-locked to the underlying low-frequency rhythm, thereby exhibiting weak PAC. Although here we show intraregional PAC, PAC can also be observed across regions. (b) Synchronous rhythmic activity following transcranial alternating current stimulation (tACS). Left: Phase-specific multisite tACS at the regions of interest leads to enhancement in interregional phase synchronization reflected in the consistent relative phases between the two regions over time following stimulation. Right: Delivering cross-frequency tACS at the region of interest leads to phase-locking of high-frequency activity to the low-frequency rhythm reflecting enhanced PAC.