Brain entrainment

The brain is entrainable

"A new unifying account of the roles of neuronal entrainment"

https://www.sciencedirect.com/science/article/pii/S0960982219309558?

Neuronal activity can be aligned to external rhythmic input streams. The phenomenon or process is called entrainment.

"Neuronal entrainment has been demonstrated in all “traditional” frequency ranges (delta, theta, alpha, beta and gamma)."  The authors argue here that entrainment is not frequency-specific.

Parallelly, they are inquiring whether frequency-specificity may "be system or brain-state specific" and to what degree.

Entrainment of a neural microcircuit

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7099485/

Featuring Figure 1

Neural circuits can adjust their frequency to a given stimulation frequency

Initially, the circuit receives a constant input, P(t)=P, and oscillates at its natural frequency, f. It then receives a sinuisoical wave input which entrains it after a certain time (convergence) to the input frequency.

The entrainment index is then calculated from the power spectrum of the signal E(t) after its convergence.

"Shaping Intrinsic Neural Oscillations with Periodic Stimulation": a computational modelling study

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6601804

Featuring Figure 2

A. Based on the selected parameters, the network shows synchronous alpha activity, with an intrinsic frequency ω0 of ~10 Hz. 

B. If the stimulation frequency ω(f) is close to the intrinsic frequency, its harmonics, and/or subharmonics, resonance occurs. While the network response frequency ω′ remains stable, the associated spectral power increases significantly. 

C. Whenever the stimulation amplitude increases beyond a certain threshold, the intrinsic activity in entrained by the stimulation drive and the network oscillates at a frequency equal to that of the stimulation, its harmonics, and/or subharmonics. In this example, a strong rhythmic stimulation ω(f) of 17.5 Hz leads to harmonic entrainment at half that frequency (subharmonic) i.e. an ω′ of 8.8 Hz. 

D. In high-frequency stimulation, nonlinear interactions account for acceleration of the ongoing synchronous activity, leading to a spectral shift. In this example, a stimulation with an ω(f) of 97 Hz accelerates the baseline activity from an ω(0) of 10 Hz to an ω′ of 15 Hz.