What is brainwave entrainment?

Brainwave entrainment, also known as 'brainwave synchronization' is a practice that depends upon a 'frequency following' response from your brain, following a dominant external stimulus. Usually, the external stimulus is a specialized software, but it can also be a pulse of sound or light.
When the brain receives an external stimulus, through ears, eyes or any other senses, it emits a response which is called a 'cortical evoked response'. These electrical responses travel throughout the brain and they can be measured using sensitive devices attached to the scalp.
When the rhythmic stimulus presented to the brain is, for example, a drum beat, the rhythm is reproduced in the brain in the form of a 'cortical evoked respose'. If the rhythm becomes fast and consistent enough, it can start to resemble the natural internal rhythms of the brain, called 'brainwaves'. When this happens, the brain starts responding by synchronizing its own electric cycles to the same rhythm as the drum beat. This is usually called a 'Frequency Following Response' or FFR.

10 fun facts about brain

Your brain stopped growing at the age of 18.

You can't tickle yourself because your brain distinguished between unexpected external touch and your own touch. 

While you sleep, your body produces a hormone that may prevent you from acting out your dreams, leaving you virtually paralyzed. 

Every time you blink, your brain kicks in and keeps things illuminated so the whole world doesn't go dark each time you blink (about 20,000 times a day). 

If you are snoring, you are not dreaming. 

Laughing at a joke is no simple task as it requires activity in five different areas of the brain. 

Just because you don't remember your dreams doesn't mean you don't dream. Everyone dreams! 

Those who are left-handed or ambidextrous have a corpus collosum (the part of the brain that bridges the two halves) that is about 11% larger than those who are right-handed. 

Brain waves are more active while dreaming than when you are awake. 

Scientists discovered that men and women's brains react differently to pain, which explains why they may perceive or discuss pain differently. 

Brainwaves described

It is very important to understand how your brain works and how it contributes to your state of mind. Most of us are used to focus on our emotions trying to become happier or a more spiritual being. What most of you don’t know is that your brain waves and your subcionscious mind play a big part in this pursuit of happiness.
Let’s take a look at your brain wave frequencies and how they affect the state of mind. Each frequency is measured in cycles per second (Hz) and has its own set of characteristics. Each of these waves represent a specific level of brain activity and a unique state of consciousness.

Let’s begin with Beta. Its range is 14-40Hz and is the wave of your wide awake state.
Beta brain waves are associated with normal waking consciousness and an increased state of alert, logic and critical reasoning.
Beta brain waves are essential for your effective functioning throughout the day, but they can also translate into a stressful, restless and anxious mind. 
Imagine Beta as that annoying little inner critic that gets louder and louder. Once it gets lounder, it means that your brain waves are high into above mentioned range and that stress is just around the corner or it has already arrived.
The majority of adults operate at Beta, this is why stress is the most common problem these days.