Neural Oscillation: What, How and Why?

Neural oscillation, also known as brainwave, is a term that describes the rhythmic or repetitive patterns of electrical activity produced by neurons in the brain and other parts of the nervous system. Neural oscillations are important for various cognitive processes, such as perception, memory, attention, motor coordination and sleep. In this post, we will explore what neural oscillations are, how they are generated and measured, and what are some of their impacts on cognition.

What is neural oscillation?

Neural oscillation is the result of a balanced interaction between two or more forces, such as excitation and inhibition, within a group of neurons. Excitation refers to the process of increasing the likelihood of a neuron to fire an action potential, which is a brief electrical signal that travels along the axon. Inhibition refers to the process of decreasing the likelihood of a neuron to fire an action potential. These processes are mediated by different types of neurotransmitters, which are chemical messengers that bind to receptors on the postsynaptic neuron.

When a group of neurons fire action potentials in synchrony, they produce a collective electrical signal that can be detected by electrodes placed on the scalp or inside the brain. This signal is called the local field potential (LFP), and it reflects the summed activity of thousands or millions of neurons. The LFP can be analyzed in terms of its frequency, amplitude and phase. Frequency refers to how fast the LFP oscillates, measured in hertz (Hz). Amplitude refers to how strong the LFP oscillates, measured in microvolts (μV). Phase refers to the position of the LFP within one cycle of oscillation, measured in radians or degrees.

There are at least 10 different types of neural oscillations, covering a wide range of frequencies from 0.02 Hz to 600 Hz. Some of the most common ones are:

• Delta waves (0.5-4 Hz): The slowest and largest-amplitude waves in the neocortex, associated with deep sleep and unconsciousness.
• Theta waves (4-8 Hz): Prominent in the hippocampus and entorhinal cortex, associated with spatial navigation and memory formation.
• Alpha waves (8-12 Hz): Dominant in the occipital cortex when the eyes are closed, associated with relaxation and reduced attention.
• Beta waves (12-30 Hz): Present in various cortical regions during alertness and cognitive tasks, associated with focused attention and problem-solving.
• Gamma waves (30-100 Hz): The fastest and smallest-amplitude waves in the neocortex, associated with sensory perception and integration.

How are neural oscillations generated?

Neural oscillations can be generated by different mechanisms at different levels of organization. At the level of individual neurons, oscillations can arise from intrinsic properties of the membrane potential or from rhythmic patterns of action potentials. For example, some neurons have pacemaker properties that allow them to fire spontaneously at a regular rate. Other neurons have resonant properties that allow them to respond preferentially to certain frequencies of input.

At the level of neuronal networks, oscillations can arise from interactions between neurons through synaptic connections or gap junctions. Synaptic connections are chemical junctions that allow neurotransmitters to modulate the activity of postsynaptic neurons. Gap junctions are electrical junctions that allow direct current flow between adjacent neurons. Both types of connections can create feedback loops that result in synchronization of neuronal firing patterns.

At the level of brain regions, oscillations can arise from interactions between different brain structures through long-range connections or neuromodulators. Long-range connections are axonal projections that link distant brain regions and allow information transfer and coordination. Neuromodulators are substances that modulate the activity of large populations of neurons through diffuse release and binding to receptors. Some examples of neuromodulators are dopamine, serotonin and acetylcholine.

How are neural oscillations measured?

Neural oscillations can be measured by various techniques that record the electrical activity of neurons or neuronal populations. Some of these techniques are:

• Electroencephalography (EEG): A non-invasive technique that measures the LFP from electrodes attached to the scalp. EEG has high temporal resolution but low spatial resolution.
• Magnetoencephalography (MEG): A non-invasive technique that measures the magnetic fields generated by neuronal currents from sensors placed around the head. MEG has high temporal resolution and better spatial resolution than EEG.
• Electrocorticography (ECoG): An invasive technique that measures the LFP from electrodes implanted on the surface of the brain. ECoG has high temporal resolution and high spatial resolution.
• Intracranial electroencephalography (iEEG): An invasive technique that measures the LFP from electrodes implanted inside the brain. iEEG has high temporal resolution and high spatial resolution.
• Single-unit recording: An invasive technique that measures the action potentials from individual neurons or small groups of neurons using microelectrodes. Single-unit recording has high temporal resolution and high spatial resolution.

What are some impacts of neural oscillations on cognition?

Neural oscillations are involved in various cognitive processes, such as perception, memory, attention, motor coordination and sleep. Some examples of how neural oscillations affect cognition are:

• Perception: Neural oscillations can modulate the sensitivity and selectivity of sensory neurons to external stimuli. For example, gamma oscillations can enhance the binding of different features of an object into a coherent percept. Theta oscillations can facilitate the integration of information across different sensory modalities.
• Memory: Neural oscillations can facilitate the encoding and retrieval of information in different memory systems. For example, theta oscillations can support the formation of episodic memories in the hippocampus and entorhinal cortex. Alpha oscillations can suppress irrelevant information and enhance relevant information in working memory.
• Attention: Neural oscillations can regulate the allocation of attentional resources to different stimuli or tasks. For example, beta oscillations can reflect the maintenance of attentional focus and the inhibition of distraction. Alpha oscillations can reflect the inhibition of irrelevant sensory input and the allocation of attention to specific spatial locations or features.
• Motor coordination: Neural oscillations can coordinate the activity of motor neurons and muscles to produce smooth and precise movements. For example, beta oscillations can reflect the maintenance of a stable posture or a steady movement. Gamma oscillations can reflect the synchronization of muscle contractions and relaxations.
• Sleep: Neural oscillations can reflect the different stages of sleep and their functions. For example, delta waves are characteristic of deep sleep, which is important for physical recovery and memory consolidation. Theta waves are characteristic of REM sleep, which is important for emotional regulation and creativity.

Conclusion

Neural oscillation is a fascinating phenomenon that reveals the complex dynamics of neuronal activity in the brain and other parts of the nervous system. Neural oscillation is generated by various mechanisms at different levels of organization, and it can be measured by various techniques with different advantages and limitations. Neural oscillation is involved in various cognitive processes, and it can modulate the performance and efficiency of these processes. Understanding neural oscillation can help us better understand how the brain works and how we can improve our cognition.

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