Signatures Of Predictive Coding: Alpha Oscillations And Travelling Waves

Signatures Of Predictive Coding: Alpha Oscillations And Travelling Waves

There are billions of neurons in different areas of the brain. These neurons communicate with each other with the help of electricity. Several of these neurons join and form a synapse. Again, several such synapses create a “neural network” linked to a particular state of consciousness, mood or thought. In a healthy brain, communication within this neural network through electrical impulses is continuous and synchronous. Such synchronous electrical activity is what we refer to as “brain wave” and travelling waves.

Oscillations in these waves can be picked up by an electroencephalogram. Depending on the bandwidth of these oscillations, brain waves have been characterized into five categories. Each of these five categories relates to a specific state of human consciousness. These brain waves change continuously and influenced by our actions, thoughts, and emotions at any given time, even when we are fast asleep. 

Signatures Of Predictive Coding: Alpha Oscillations And Travelling Waves
Signatures Of Predictive Coding: Alpha Oscillations And Travelling Waves

Alpha Waves And Travelling Waves

Alpha wave is one of these five types of waves, and it is found when the brain is typically idling. So when does the brain idle? It usually does so when you are consciously practicing meditation or mindfulness or are in a state of daydreaming. You create these waves also when you do aerobic exercises.

Alpha oscillations are typically prominent when the sensory inputs are minimal, and the mind is mostly clear of unwanted thoughts. During such phases, the brain focuses on specific thoughts, which may be positive or negative. However, these waves usually disappear when higher frequency waves gain momentum. So, these waves are linked to a relaxed mind, and this is important in any biofeedback training. An EEG can offer continuous feedback about the increase or decrease of alpha waves.

Hierarchical Predictive Coding: Travelling Waves

The brain receives various input data from different sensory stimulations such as tactile, olfactory, etc. and makes predictive assumptions depending on stored information from previous knowledge about that particular stimulus. This is again adjusted by corrected feedback from further incoming data. So, the brain constructs probable versions of sensory input using what the predictive coding system of the brain has learned about the likely outcome from previous knowledge.

Signatures Of Predictive Coding: Alpha Oscillations And Travelling Waves
Signatures Of Predictive Coding: Alpha Oscillations And Travelling Waves

Alpha Wave And Predictive Coding

Research has shown that a simple 2-level predictive coding model of visual cortex gives rise to alpha-band rhythms. A multilevel version of this model has also demonstrated forward alpha travelling waves across different levels during visual stimulation and backward during rest. The predictions have also matched two independent electroencephalography tests since they observed travelling waves in both forward and backward directions.

Alpha wave oscillations in the region of 8–12 Hz are the most prominent oscillations in the brain. In the experiments conducted, significant input-output correlation is quite surprising. Moreover, a recent study showed that alpha-band oscillations propagate as travelling waves across the cortex to the frontal, i.e. across multiple levels. This also corresponds to recent intracranial studies which exhibited alpha-band travelling waves across the cortex. However, the mechanism of these oscillations is still not widely acceptable.  

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