Understanding Brainwave Entrainment: A Deep Dive into Neuronal Activity
Neurons are the fundamental signaling units of the brain. Each neuron has a basic structure consisting of dendrites, the cell body (soma), and the axon. Dendrites receive signals from other nerve cells, the somaacts as the cell’s metabolic center housing the nucleus, and the axon is responsible for transmitting signals. An axon can carry electrical signals over distances ranging from 0.1 mm to 1 m. These electrical signals, known as action potentials, can propagate at speeds of 1 to 100 m/s. Action potentials enable the brain to receive, analyze, and transmit information (Kandel et al., 2023).
Human brainwaves are rhythmic patterns of neural activity in the central nervous system (CNS), representing the electrical voltages produced by groups of neurons activating together, typically measuring a few millionths of a volt (Abhang et al., 2016; Tatum, 2014). These waves can be characterized by frequency, amplitude, and phase, coordinating brain activity and facilitating signal transmission between brain regions (Headley & Paré, 2017). It is known that coherent and functional brainwave patterns are crucial for successful task execution, whether physical or mental (Tang et al., 2016) and that different brain regions can emit different frequencies simultaneously (Abhang et al., 2016).
Excitatory and inhibitory interactions within brain circuits operate across various timescales, influencing the emergence of oscillations at different frequencies. These oscillations span a spectrum from slowest to fastest, encompassing delta, theta, alpha, beta, gamma, and sharp-wave ripples. They display distinct temporal and regional patterns throughout the brain and are theorized to play essential roles in cognitive functions, such as memory (Adaikkan and Tsai, 2019).
Brain oscillatory rhythms in the 1-30 Hz range can be modulated or entrained by external stimuli. Entrainment occurs when a group of neurons in a stimulated area synchronizes their activity with an external rhythm (Figure 1). This process involves two main effects: first, an increase in signal strength as more neurons align their phases with the external rhythm; second, the synchronization of the entire neuronal population to this rhythm. This synchronization doesn’t happen instantly but evolves over time, influenced by the intensity of the stimulation (Thut et al., 2011; Hanslmayr et al., 2019).
Brainwaves are evident in extracellular electric fields and can be detected by various methods. The most popular is EEG, a noninvasive technique using scalp electrodes (Abhang et al., 2016; Joshi et al., 2019). More invasive methods like electrocorticography and local field potential recording provide higher spatial and temporal resolution but require electrode implantation in the cerebral cortex (Joshi et al., 2019).
Therefore, Brainwave Entrainment (BWE) therapy posits that auditory or visual stimulation at specific frequencies can modulate the brain’s electrocortical activity. This potential is intriguing because it suggests the possibility of inducing specific physiological and psychological states through designed external stimuli with particular frequency bands (Ingendoh et al., 2023).
By understanding and harnessing these rhythmic brainwave patterns, BWE therapy aims to enhance mental and physical performance, opening new avenues for therapeutic and cognitive interventions.
Figure 1. Neurons are entrained either by a continuous stimulus (sine wave) or pulses of stimuli. The raster plot displays simulated spiking activity in a neural population, while the local field potential (LFP)/EEG (electroencephalography) illustrates the population-level activity. The upper right panel indicates the phase difference between the entraining stimulus and population activity, with colors marking time from the beginning (green) to the end (red) of entrainment.
Source: Hanslmayr et al., 2019
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