Welcome to the I Can't Sleep Podcast,
Where I read random articles from across the web to bore you to sleep with my soothing voice.
I'm your host,
Benjamin Boster,
And today's episode is from a Wikipedia article titled Neural Network.
A neural network is a group of interconnected units,
Called neurons,
That send signals to one another.
Neurons can be either biological cells or mathematical models.
While individual neurons are simple,
Many of them together in a network can perform complex tasks.
There are two main types of neural networks.
In neuroscience,
A biological neural network is a physical structure found in brains and complex nervous systems.
A population of nerve cells connected by synapses.
In machine learning,
An artificial neural network is a mathematical model used to approximate nonlinear functions.
Artificial neural networks are used to solve artificial intelligence problems.
In the context of biology,
A neural network is a population of biological neurons chemically connected to each other by synapses.
A given neuron can be connected to hundreds of thousands of synapses.
Each neuron sends and receives electrochemical signals called action potentials to its connected neighbors.
A neuron can serve an exitory role,
Amplifying and propagating signals it receives,
Or an inhibitory role,
Suppressing signals instead.
Populations of interconnected neurons that are similar than neural networks are called neural circuits.
Very large interconnected networks are called large-scale brain networks,
And many of these together form brains and nervous systems.
Signals generated by neural networks in the brain eventually travel through the nervous system and across neuromuscular junctions to muscle cells,
Where they cause contraction and thereby motion.
In machine learning,
A neural network is an artificial mathematical model used to approximate nonlinear functions.
While early artificial neural networks were physical machines,
Today they're almost always implemented in software.
Neurons in an artificial neural network are usually arranged into layers,
With information passing from the first layer,
The input layer,
Through one or more intermediate layers,
The hidden layers,
To the final layer,
The output layer.
The signal input to each neuron is a number,
Specifically a linear combination of the outputs of the connected neurons in the previous layer.
The signal each neuron outputs is calculated from this number according to its activation function.
The behavior of the network depends on the strengths,
Or weights,
Of the connections between neurons.
A network is trained by modifying these weights through empirical risk minimization,
Or back propagation,
In order to fit some pre-existing dataset.
Neural networks are used to solve problems in artificial intelligence,
And have thereby found applications in many disciplines,
Including predictive modeling,
Adaptive control,
Facial recognition,
Handwriting recognition,
General game playing,
And generative AI.
The theoretical base for contemporary neural networks was independently proposed by Alexander Bain in 1873 and William James in 1890.
Both posited that human thought emerged from interactions among large numbers of neurons inside the brain.
In 1949,
Donald Hebb described Hebbian learning,
The idea that neural networks can change and learn over time by strengthening a synapse every time a signal travels along it.
Artificial neural networks were originally used to model biological neural networks starting in the 1930s,
Under the approach of connectionism,
However,
Starting the invention of the perception a simple artificial neural network by Warren McCulloch and Walter Pitts in 1943,
Followed by the implementation of one in hardware by Frank Rosenblatt in 1957.
Artificial neural networks become increasingly used for machine learning applications instead,
And increasingly different from their biological counterparts.
Neuroscience is the scientific study of the nervous system,
The brain,
Spinal cord,
And peripheral nervous system,
Its functions,
And its disorders.
It is a multidisciplinary science that combines physiology,
Anatomy,
Molecular biology,
Developmental biology,
Cytology,
Psychology,
Physics,
Computer science,
Chemistry,
Medicine,
Statistics,
And mathematical modeling to understand the fundamental and emergent properties of neurons,
Glia,
And neural circuits.
The understanding of the biological basis of learning,
Memory,
Behavior,
Perception,
And consciousness have been described by Eric Handel as the epic challenge of the biological sciences.
The scope of neuroscience has broadened over time to include different approaches used to study the nervous system at different scales.
The techniques used by neuroscientists have expanded enormously,
From molecular and cellular studies of individual neurons to imaging of sensory,
Motor,
And cognitive tasks in the brain.
The earliest study of the nervous system dates to ancient Egypt.
Manuscripts dating to 1700 BC indicate that the Egyptians had some knowledge about symptoms of brain damage.
In Egypt from the late Middle Kingdom onwards,
The heart was the seed of intelligence.
The view that the heart was the source of consciousness was not challenged until the time of the Greek physician Hippocrates.
He believed that the brain was not only involved with sensation,
Since most specialized organs like the eyes,
Ears,
And tongue are located in the head near the brain,
But was also the seed of intelligence.
Plato also speculated that the brain was the seed of the traditional part of the soul.
Aristotle,
However,
Believed the heart was the center of intelligence,
And that the brain regulated the amount of heat from the heart.
This view was generally accepted until the Roman physician Galen,
A follower of Hippocrates and physician to Roman gladiators,
Observed that his patients lost their mental faculties when they had sustained damage to their brains.
Luigi Galvani's pioneering work in the late 1700s set the stage for studying the electrical excitability of muscles and neurons.
In 1843,
Emile de Bois Raymond demonstrated the electrical nature of the nerve signal,
Whose speed Hermann von Helmholtz proceeded to measure,
And in 1875 Richard Caton found electrical phenomena in the cerebral hemispheres of rabbits and monkeys.
Adolph Beck published in 1890 similar observations of spontaneous electrical activity of the brain of rabbits and dogs.
Studies of the brain became more sophisticated after the invention of the microscope and the development of a staining procedure by Camillo Golgi during the late 1890s.
The procedure used is silver chromate salt to reveal the intricate structures of the individual neurons.
His technique was used by Santiago Ramon y Cajal and led to the formation of the neuron doctrine,
The hypothesis that the functional unit of the brain is the neuron.
Golgi and Ramon y Cajal shared the Nobel Prize in Physiology or Medicine in 1906 for their extensive observations,
Descriptions,
And categorizations of neurons throughout the brain.
During the 20th century,
Neuroscience began to be recognized as a distinct academic discipline in its own right,
Rather than as studies of the nervous system within other disciplines.
Eric Handel and collaborators have cited David Rioch,
Francis O.
Schmidt,
And Stephen Koeffler as having played critical roles in establishing the field.
Rioch originated the integration of basic anatomical and physiological research with clinical psychiatry at the Walter Reed Army Institute of Research starting in the 1950s.
During the same period,
Schmidt established a neuroscience research program within the biology department of the Massachusetts Institute of Technology,
Bringing together biology,
Chemistry,
Physics,
And mathematics.
The first freestanding neuroscience department,
Then called psychobiology,
Was founded in 1964 at the University of California,
Irvine by James L.
McGough.
This was followed by the department of neurobiology at Harvard Medical School,
Which was founded in 1966 by Stephen Koeffler.
In the process of treating epilepsy,
Wilder Penfield produced maps of the location of various functions—motor,
Sensory,
Memory,
Vision—in the brain.
He summarized his findings in a 1950 book called The Cerebral Cortex of Man.
Wilder Penfield and his co-investigators Edwin Bouldry and Theodore Rasmussen are considered to be the originators of the cortical homunculus.
The understanding of neurons and of nervous system function became increasingly precise and molecular during the 20th century.
For example,
In 1952,
Alan Lloyd Hodgkin and Andrew Huxley presented a mathematical model for the transmission of electrical signals in neurons of the giant axon of a squid,
Which they called action potentials,
And how they are initiated and propagated,
Known as the Hodgkin-Huxley model.
In 1961-62,
Richard Fixhugh and Jay Nagumo simplified Hodgkin-Huxley in what is called the Fixhugh-Nagumo model.
In 1962,
Bernard Kotz modeled neurotransmission across the space between neurons,
Known as synapses.
Beginning in 1966,
Eric Kandel and collaborators examined biochemical changes in neurons associated with learning and memory storage in aplesia.
In 1981,
Catherine Morris and Harold Lecker combined these models in the Morris-Lecker model.
Such increasingly quantitative work gave rise to numerous biological neuron models and models of neurocomputation.
As a result of the increasing interest about the nervous system,
Several prominent neuroscience organizations have been formed to provide a forum to all neuroscientists during the 20th century.
For example,
The International Brain Research Organization was founded in 1961,
The International Society for Neurochemistry in 1963,
The European Brain and Behavior Society in 1968,
And the Society for Neuroscience in 1969.
Recently,
The application of neuroscience research results has also given rise to applied disciplines as neuroeconomics,
Neuroeducation,
Neuroethics,
And neurolaw.
Over time,
Brain research has gone through philosophical,
Experimental,
And theoretical phases,
With work on neural implants and brain simulation predicted to be important in the future.
The scientific study of the nervous system increased significantly during the second half of the 20th century,
Principally due to advances in molecular biology,
Electrophysiology,
And computational neuroscience.
This has allowed neuroscientists to study the nervous system in all its aspects,
How it is structured,
How it works,
How it develops,
How it malfunctions,
And how it can be changed.
For example,
It has become possible to understand in much detail the complex processes occurring within a single neuron.
Neurons are cells specialized for communication.
They are able to communicate with neurons and other cell types through specialized junctions called synapses,
At which electrical or electrochemical signals can be transmitted from one cell to another.
Many neurons extrude a long,
Thin filament of axoplasm called an axon,
Which may extend to distant parts of the body and are capable of rapidly carrying electrical signals influencing the activity of other neurons,
Muscles,
Or glands at the termination points.
A nervous system emerges from the assemblage of neurons that are connected to each other in neural circuits and networks.
The vertebrate nervous system can be split into two parts,
The central nervous system,
Defined as the brain and spinal cord,
And the peripheral nervous system.
In many species,
Including all vertebrates,
The nervous system is the most complex organ system in the body,
With most of the complexity residing in the brain.
The human brain alone contains around 100 billion neurons and 100 trillion synapses.
It consists of thousands of distinguishable substructures connected to each other in synaptic networks whose intricacies have only begun to be unraveled.
At least one out of three of the approximately 20,
000 genes belonging to the human genome is expressed mainly in the brain.
Due to the high degree of plasticity of the human brain,
The structure of its synapses and the resulting functions change throughout life.
Making sense of the nervous system's dynamic complexity is a formidable research challenge.
Ultimately,
Neuroscientists would like to understand every aspect of the nervous system,
Including how it works,
How it develops,
How it malfunctions,
And how it can be altered or repaired.
Analysis of the nervous system is therefore performed at multiple levels,
Ranging from the molecular and cellular levels to the systems and cognitive levels.
The specific topics that form the main focus of research change over time,
Driving by an ever-expanding base of knowledge and the availability of increasingly sophisticated technical methods.
Improvements in technology have been the primary drivers of progress.
Developments in electron microscopy,
Computer science,
Electronics,
Functional neuroimaging,
And genetics and genomics have all been major drivers of progress.
Advances in the classification of brain cells have been enabled by electrophysiological recording,
Single-cell genetic sequencing,
And high-quality microscopy,
Which have combined into a single-method pipeline called patch sequencing,
In which all three methods are simultaneously applied using miniature tools.
The efficiency of this method and the large amounts of data that is generated has allowed researchers to make some general conclusions about cell types.
For example,
That the human and mouse brain have different versions of fundamentally the same cell types.
Basic questions addressed in molecular neuroscience include the mechanisms by which neurons express and respond to molecular signals and how axons form complex connectivity patterns.
At this level,
Tools from molecular biology and genetics are used to understand how neurons develop and how genetic changes affect biological functions.
The morphology,
Molecular identity,
And physiological characteristics of neurons and how they relate to different types of behavior are also of considerable interest.
Questions addressed in cellular neuroscience include the mechanisms of how neurons process signals physiologically and electrochemically.
These questions include how signals are processed by neurites and somas and how neurotransmitters and electrical signals are used to process information in a neuron.
Neurites are thin extensions from a neuronal cell body consisting of dendrites specialized to receive synaptic inputs from other neurons and axons specialized to conduct nerve impulses called action potentials.
Somas are the cell bodies of the neurons and contain the nucleus.
Another major area of cellular neuroscience is the investigation of the development of the nervous system.
Questions include the patterning and regionalization of the nervous system,
Axonal and dendritic development,
Trophic interactions,
Synapse formation,
And the implication of fractions in neural stem cells,
Differentiation of neurons and glia,
Neurogenesis and gliogenesis,
And neuronal migration.
Computational neurogenetic modeling is concerned with the development of dynamic neuronal models for modeling brain functions with respect to genes and dynamic interactions between genes on the cellular level.
Computational neurogenetic modeling,
CNGM,
Can also be used to model neurosystems.
Systems Neuroscience Research Center is on the structural and functional architecture of the developing human brain and the functions of large-scale brain networks or functionally connected systems within the brain.
Alongside brain development,
Systems neuroscience also focuses on how the structure and function of the brain enables or restricts the processing of sensory information using learned mental models of the world to motivate behavior.
Questions in systems neuroscience include how neural circuits are formed and used anatomically and physiologically to produce functions such as reflexes,
Multisensory integration,
Motor coordination,
Circadian rhythms,
Emotional responses,
Learning,
And memory.
In other words,
This area of research studies how connections are made and morphed in the brain and the effect it has on human sensation,
Movement,
Attention,
Inhibitory control,
Decision-making,
Reasoning,
Memory formation,
Reward,
And emotional regulation.
Specific areas of interest for the field include observations of how the structure of neural circuits affects skill acquisition,
How specialized regions of the brain develop and change,
Neuroplasticity,
And the development of brain atlases or wiring diagrams of individual developing brains.
The related fields of neuroethology and neuropsychology address the question of how neural substrates underlie specific animal and human behaviors.
Neuroendocrinology and psychoneuroimmunology examine interactions between the nervous system and the endocrine and immune systems,
Respectively.
Despite many advancements,
The way that networks of neurons perform complex cognitive processes and behaviors is still poorly understood.
Cognitive neuroscience addresses the questions of how psychological functions are produced by neurocircuitry.
The emergence of powerful new measurement techniques,
Such as neuroimaging,
E.
G.
FMRI,
PET,
SPECT,
EEG,
MAG,
Electrophysiology,
Optogenetics,
And human genetic analysis combined with sophisticated experimental techniques from cognitive psychology allows neuroscientists and psychologists to address abstract questions,
Such as how cognition and emotion are mapped to specific neural substrates.
Although many studies hold a reductionist stance looking for the neurobiological basis of cognitive phenomena,
Recent research shows that there is an interplay between neuroscientific findings and conceptual research,
Soliciting and integrating both perspectives.
For example,
Neuroscience research on empathy solicited an interdisciplinary debate involving philosophy,
Psychology,
And psychopathology.
Moreover,
The neuroscientific identification of multiple memory systems related to different brain areas has challenged the idea of memory as a literal reproduction of the past,
Supporting a view of memory as a generative,
Constructive,
And dynamic process.
Neuroscience is also allied with social and behavioral sciences,
As well as with nascent interdisciplinary fields.
Examples of such alliances include neuroeconomics,
Decision theory,
Social neuroscience,
And neuromarketing to address complex questions about interactions of the brain with its environment.
A study into consumer responses,
For example,
Uses EEG to investigate neural correlations associated with narrative transportation into stories about energy efficiency.
Questions in computational neuroscience can span a wide range of levels of traditional analysis,
Such as development,
Structure,
And cognitive functions of the brain.
Research in this field utilizes mathematical models,
Theoretical analysis,
And computer simulation to describe and verify biological plausible neurons and nervous systems.
For example,
Biological neuron models are mathematical descriptions of spiking neurons,
Which can be used to describe both the behavior of single neurons as well as the dynamics of neural networks.
Computational neuroscience is often referred to as a theoretical neuroscience.
Neurology,
Psychiatry,
Neurosurgery,
Psychosurgery,
Anesthesiology,
And pain medicine,
Neuropathology,
Neuroradiology,
Ophthalmology,
Otolaryngology,
Clinical neurophysiology,
Addiction medicine,
And sleep medicine are some medical specialties that specifically address the diseases of the nervous system.
These terms also refer to clinical disciplines involving diagnosis and treatment of these diseases.
Neurology works with diseases of the central and peripheral nervous systems,
Such as amyotrophic lateral sclerosis,
ALS,
And stroke,
And their medical treatment.
Psychiatry focuses on affective,
Behavioral,
Cognitive,
And perceptual disorders.
Anesthesiology focuses on perception of pain and pharmacological alteration of consciousness.
Neuropathology focuses upon the classification and underlying pathogenic mechanisms of central and peripheral nervous system and muscle diseases,
With an emphasis on morphologic,
Microscopic,
And chemical observable alterations.
Neurosurgery and psychosurgery work primarily with surgical treatment of diseases of the central and peripheral nervous systems.
Recently,
The boundaries between various specialties have blurred,
As they are all influenced by basic research in neuroscience.
For example,
Brain imaging enables objective biological insight into mental illnesses,
Which can lead to faster diagnosis,
More accurate prognosis,
And improved monitoring of patient progress over time.
Integrative neuroscience describes the effort to combine models and information from multiple levels of research to develop a coherent model of the nervous system.
For example,
Brain imaging coupled with physiological numerical models and theories of fundamental mechanisms may shed light on psychiatric disorders.
Another important area of translational research is brain-computer interfaces,
BCIs,
Or machines that are able to communicate and influence the brain.
They are currently being researched for their potential to repair neural systems and restore certain cognitive functions.
However,
Some ethical considerations have to be dealt with before they are accepted.
