Brain Network System

The brain is a complex organ. It performs a variety of functions. However, for the brain to be able to function at its best it needs to rely on its nerve conductors. The brain is characterized by heterogeneous patterns of structural connections that support cognition and a variety of behaviors.

The brain is a complicated system of interconnected cells. Johnson and Wu give a rough estimate of the human brain - 10¹² neurons with 10¹⁵ synapses. If you are going to wrap your head around a magnitude of 10¹⁵ synapses, it could probably be 222 times greater than the distance of the earth to Pluto in a square meter. (1)

The brain network system consists of neurons or nerve cells and their primary goal is to transmit and process information received from our senses. the nerve cells are arranged together in the brain forming a network of nerves. They pass electrical impulses with the following:

• Dendrites –they receive impulses from the synapse (terminal button) of the adjoining neuron. They carry impulses to the nerve cell’s nucleus or soma.
• Axon –It is the longer branch among the dendrites and carries electrical impulses from the soma to the synapse.
• Synapse – It is a structure in the brain that allows the neuron to pass an electrical/chemical signal to another neuron or the effector cells.

In the human brain, there is a complex network of neurons that encompass brain network systems. These neurons need to interact with each other to create a brain network system.

The interaction between different neurons in the brain is needed to communicate and process information according to what we see, hear, think, and move. The brain network system is the heart of all activity in the body. (2)

The Brain Network System as a Modern-day Computer

The brain functions the same way as the modern-day computer. There is an input, output, storage, processing, and program.

• Inputs – They pertain to stimuli, objects, or data that cause action. In a computer, the inputs come through an input device such as a mouse, keyboard, a camera, or a scanner. They vary in formats such as text, images, and other structured data. In the human brain, the inputs are in the forms of external and internal stimuli. Sensory cells are primarily involved in inputs such as seeing, touching, hearing and tasting. Motor cells and some cells in the brain also serve as inputs.
• Output – it pertains to action or information caused by processing the input. If you compare it to a machine, the output can be in the forms of printing something or projecting images. In the human brain, the output pertains to activities that cause you to control both internal and external muscles. It also includes sensory perception, decision-making, emotions, problem-solving, management of internal body functions such as heart rate, blood pressure, and temperature, and social behavior.
• Storage – it is where the input and output information and programs are stored. In a computer, it has two types of storage – short-term and long-term storage. The short-term storage is in the form of an RMA, which stores a limited amount of information needed to perform an immediate task. The long-term storage is in the form of an optical disk, hard disk drives, and tapes, to name a few. They have greater storage capacity. The storage in the human brain pertains to the memory system. The short-term storage is called working memory. It uses the brain’s memory and attention capability in performing an immediate task such as jotting down what the teacher says in a class. On the other hand, long-term memory has the ability to store an unlimited amount of information for an indefinite time. It pertains to the brain’s ability to recall specific events, experiences, and other factual information. (3)
• Processor –It pertains to the central processing circuit that carries out instructions. If you are going to compare the human brain to a computer, the processor is the central processing unit. For humans, it pertains to the central nervous system. It consists of a person’s brain, spinal cord, and internal circuitry.
• Program/Code –it pertains to a set of instructions containing what needs to be done with the input to convert into output thereby leading in a set of functions that need to be performed. In the human brain, the code is executed through the neurons in the brain. They make connections with each other and pass on signals to process the desired actions. The entire process is controlled by the central nervous system. The exchange of information takes place through critical nervous system structures (synapses). The human brain runs its code through a pattern of chemical/electrical signals and passes from one neuron to another thereby forming a neural network.

Analyzing the Brain Network System

The observation
of Brain networks can be done in two ways – anatomical and physiological
leading to functional and structural networks.

The Structural Connectivity of the brain

It pertains to the anatomical connections in the brain that link a set of neural elements, specifically the regions cortical and subcortical. Structural connectivity tends to be stable on a short time scale – ranging between seconds to minutes.

However, it can be subjected to plastic experience-dependent modifications at a longer time frame, which could be several hours to days. The structure of the brain’s connectivity is measured in a set of undirected links. (4)

The Functional Connectivity of the Brain

It is acquired from time-series observations. It also shows the pattern of statistical dependence among the different types of neural elements.

There are a variety of techniques that can be used to observe time-series data such as EEG or electroencephalography, MEG or magnetoencephalography, fMRI or and functional magnetic resonance imaging, to name a few.

The functional connectivity of the brain is time-dependent and changes in a span of tens or hundreds of milliseconds. The sensory stimuli and task context regulate the functional connections of the brain.

The Effective Connectivity of the Brain

It is also used as a method of representing and analyzing the brain network system. It captures a network od directed causal effects between different neural elements.

Effective connectivity represents both generative and mechanistic models leading to observed data derived from a variety of possible models. The effective connectivity of studying the brain network system is pretty new. The majority of brain network study is carried out using the structural and functional connectivity.

The Different Types of Brain Network System

1. Default mode – It is active when the person is awake and at rest. The default mode brain network system is activated if the person focuses on an internally-oriented task such as:
   1. Dreaming of the future
   1. Day-dreaming
   1. Recalling memories
   1. Theory of mind
2. Dorsal attention – It pertains to voluntary giving of attention as well as a reorientation to unexpected situations.
3. Ventral attention – It pertains to the person's response to behaviorally relevant stimuli that happens suddenly.
4. Fronto-parietal –It is the system in the brain that initiates and modulates cognitive control.
5. Salience – It tracks down the salience of internal brain events and external inputs.
6. Lateral visual –it plays an important role in complex emotional stimuli. (5)

References

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5485642/
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4854276/
3. https://www.annualreviews.org/doi/abs/10.1146/annurev-neuro-062111-150525
4. https://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1004029
5. https://www.omicsonline.org/scholarly/neural-network-journals-articles-ppts-list.php