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- Herausgeber: Bentham Science Publishers
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
The Brain: A Systems Neuroscience Perspective is a comprehensive textbook designed for undergraduate students in neuroscience. It offers a detailed exploration of brain dynamics, spatial navigation, and the neuroscience of Alzheimer's disease, with an emphasis on understanding complex concepts through simplified mathematical models. The objective is to provide a solid foundation for readers in systems neuroscience.
Key Topics
Fundamental Brain Dynamics: Covers the basics of brain organization, neural systems, and the role of differential equations in neuroscience (Chapters 1-3).
Spatial Navigation: Discusses the neural mechanisms underlying spatial navigation and the geometry of neural maps (Chapter 4).
Alzheimer’s Disease: Presents a simplified mathematical theory of Alzheimer’s dementia, exploring its onset, progression, and potential interventions (Chapter 5).
Key Features
Accessible Approach: Minimizes mathematical complexity to make the subject approachable for readers with a basic understanding of differential equations.
Standalone Resource: Provides all essential knowledge on brain function, making it a valuable tool for both coursework and self-study. Includes references for advanced readers.
Readership
Undergraduate neuroscience students and researchers who require a foundation in systems neuroscience.
Das E-Book können Sie in Legimi-Apps oder einer beliebigen App lesen, die das folgende Format unterstützen:
Seitenzahl: 173
Veröffentlichungsjahr: 2024
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PREFACE
It is ‘the brain’ that stops functioning at the end of the journey of a living entity. The brain is a complex system. It is made up of many subsystems. A complex system means ‘whole’ is not a sum of the parts. It is characterized by emergent behavior. Therefore, there is an urgent need to understand it as it is. Reductionism of basic sciences does not apply to the human brain. The book is prepared for undergraduate students and instructors working at that level. It is organized as follows:
The first chapter describes the subsystems mentioned in the first paragraph. The central nervous system, sympathetic nervous system, and parasympathetic nervous system are discussed first, as these are the most crucial for the functioning of the brain. Concepts such as cerebrospinal fluid, blood-brain barrier, and blood-cerebrospinal fluid barrier are presented in such a way that even a novice in neurosciences would be able to grasp the fundamentals easily. Neurons and glial cells are discussed next (Chapter 2). Imaging techniques that are employed in the diagnostics of brain disorders and neurodegenerative diseases are also presented in this chapter.
The subsystems of the brain are made of neurons and glial cells. These cells participate in cellular signaling. Thus, cross-talk between different subsystems becomes a reality. This happens either electrically or chemically. The information transport in the brain is discussed in Chapter 3. Spatial navigation is an essential part of life. A living entity executes it for different purposes, e.g., to search for food or better habitat. Therefore, a complete chapter (chapter 4) is devoted to this topic.
Chapter 5 presents a mathematical theory of Alzheimer’s disease. This theory posits amyloid β in a new light. It introduces femto particles for the first time. Femto particles are proton–antiproton entangled pairs. It has been shown that these particles have the potential to revolutionize research on Alzheimer’s disease, both with respect to detecting the disease at an early stage and discovering drug molecules that could cure the disease. At the end of this chapter, a set of parameters is given that a clinician can use to detect Alzheimer’s disease, which is known to be a silent, deadly disease. The last chapter presents the neuroscience of romanticism, a literary movement that has influenced the literature of almost all languages. It resolves to define and refine the idea of beauty for Homo sapiens.
I hope the book fulfills its purpose.
Elements of Organization
Vikas Rai1,*Abstract
The lives of species are trapped within ‘cooperation and conflict’. They compete with each other to win the ‘survival of the fittest’. In cognitive neurosciences, action and perception are the most crucial. Perception guides action by selecting targets and correcting errors. This entire process is stored in the memory. It is an essential part of learning and creates the basis for new knowledge by association. Neural circuits that control metabolism and food intake are housed within the hypothalamus. It is small in size but plays a crucial role. Temperature, sleep, eating, and social interactions are its responsibility. Emotion and learning are related e.g., positive emotion (simply feeling good) motivates students to perform better. Emotion, as the present state of knowledge stands, is taken care of by the amygdala. Should we consider it the ‘heart of the brain’?
The purpose of this chapter is not to cover all systems or subsystems but to discuss only a select few. This decision has been taken to reduce the complexity of the brain’s neurovascular structure. Capillaries in the neurovascular structure hold back certain molecules, RNA viruses, and other disease-causing agents (ions, molecules, etc). The blood-brain barrier, cerebrospinal fluid, and blood-cerebrospinal fluid barrier are three key elements of the organizational structure of the brain.
INTRODUCTION
Life is full of rhythms. Pulsations in the heart are represented by the Van der Pol Oscillator.
(1)x represents the cumulative charge in the blood that the heart pumps. The limit cycle of this oscillator represents robust electrical oscillations of the heart, which continue till the doctor pronounces the patient ‘brain dead’.
The blood-brain barrier (BBB) controls the influx and efflux of biological substances essential for homeostasis of the brain’s microenvironment represented by the neurovascular unit. Blood vessels in the brain capillaries form the vascular structure, which controls the movement of ions, molecules, and viruses of various kinds.
Paragraphs that follow discuss key elements of the organization.
CENTRAL, PARASYMPATHETIC AND SYMPATHETIC NERVOUS SYSTEMS
Electrical signals are responsible for transferring information over long distances within neural systems. Chemical signals are involved in the transmission of information between neurons. Synaptic and action potentials are caused by transient changes in current flow into and out of the neuron. This flow of current in and out of the neuron drives the electrical potential across the plasma membrane away from its resting condition. The transient current flow is caused by ion channels, a class of integral proteins that traverse the cell membrane. The purpose of the nervous system is to transfer information from the peripheral nervous system (PNS) to the CNS and send back the information to the PNS. The transfer of information from the external environment and back again is known as neuronal signaling.
Fig. (1)) Central, parasympathetic, and sympathetic nervous systems. The cross-talk between these systems is crucial for the functioning of the brain.The central nervous system (cf. Fig. 1) is a part of the nervous system that consists of the brain and the spinal cord. The peripheral nervous system connects the CNS to sensory organs such as the eye and ear, other organs of the body, muscles, blood vessels, and glands. The peripheral nerves include the 12 cranial nerves, the spinal nerves, and the roots and autonomic nerves, which are concerned specifically with the regulation of the heart muscle, the muscles in blood vessel walls, and ‘glands’.
The parasympathetic nervous System (PNS) contains both kinds of fibers. These fibers provide sensory input and motor output to the CNS. PNS is a component of the autonomic nervous system that participates in the regulation of bodily functions at rest and during non–stressful situations. It slows down heart rate, decreases blood pressure, and promotes digestion. Conservation of energy, relaxation of muscles, and maintenance of bodily equilibrium after stress or physical activity are its primary responsibilities. The sympathetic nervous system functions to produce localized adjustments, such as sweating, as a response to an increase in temperature, and reflex adjustments of the cardiovascular system. Under the conditions of stress, the entire sympathetic nervous system is activated and produces a fight-or-flight response. Autonomic nervous system (ANS) refers to collections of motor neurons (ganglia) situated in the head, neck, thorax, abdomen and pelvis and the axonal collection of the neurons. The CNS components of the ANS include brain stem and spinal autonomic pre-ganglionic neurons that project to the autonomic motor neurons in the peripheral ganglia.
ENTERIC NERVOUS SYSTEM
It is the largest and most complex component of the peripheral nervous system, with approximately 600 million neurons. These neurons release neurotransmitters to facilitate the motor, sensory, and secretary functions of the gastrointestinal tract. The enteric nervous system interacts with the gut-brain axis. CNS communicates with ENS via the vagus nerve and pre-vertebral ganglia. The functions of ENS are affected by CNS in relation to emotional and cognitive factors. The control of gastrointestinal motility and secretion is mediated through a communication link between smooth muscle cells and glands. The sensory information from the gut is relayed to the CNS, affecting the digestive processes. The neurotransmitters used by ENS are acetylcholine, dopamine, and serotonin.
In the next two sections, limbic and reward systems are discussed.
Limbic System
It is present at the border of the cerebral cortex and subcritical structures of the diencephalon (cf. Fig. 2). It participates in emotion, pleasure and reinforcement; emotion is its primary engagement. Emotion is responsible for the complex behavioral patterns of human beings. It is handled by a group of structures in the brain. Underneath the cerebral cortex and above the brainstem, structures of the limbic system are buried deep within the brain. The amygdala and hippocampus are two of its major structures. The thalamus, hypothalamus and basal ganglia also support the activities of the limbic system. The amygdala in the temporal lobe, with an almond-like shape, is involved in a wide range of emotions. New memories specifically related to fear are formed in it. The hippocampus is associated with memory. Our ability to navigate the word is supported by this part of the cortex. A sense of spatial orientation is generated by a group of participating neurons in the hippocampus. An area of the cortex that surrounds the hippocampus is known as the parahippocampal gyrus. It is associated with pleasurable memory.
Fig. (2)) Limbic system; Source: Dreamstime.comAdult stem cells organize to form new neurons in a process called neurogenesis, which is responsible for the brain’s plasticities.
Septal nuclei are sub-cortical and are initially implicated by early ablation and simulation studies on the regulation of emotional responses associated with rage behavior. Septal nuclei are connected with other limbic structures. They are associated with pleasurable work and reinforcement. Bodily states that maintain homeostasis are controlled by memories stored in the connections at the interface of the hypothalamus and pituitary gland. Mammillary Bodies are brainstem nuclei extensively connected with the amygdala and hippocampus. Fornix fiber bundles carry information from the hippocampus to the mammillary bodies.
Reward System
How the brain responds to natural rewards (e.g., energy-rich foods, sex, etc.) and drugs must be clearly understood. Following are brain structures associated with rewards (cf. Fig. 3).
Reward-related brain structures
Nucleus AccubensPrefrontal CortexAmygdalaHippocampusOur pleasure-seeking behavior motivates us to achieve goals that we set for ourselves. Neurotransmitters help shape our thoughts and behaviors. Dopamine is the neurotransmitter that is associated with ‘pleasure’. It is primarily produced in the midbrain and is subsequently transported to other areas of the brain, e.g., the amygdala. The amygdala is the brain region associated with ‘emotion’ and, therefore, can be considered the ‘heart of the brain’. It is also transported to the prefrontal cortex, a brain region associated with thinking, feeling, and taking big actions.
Drug-induced pathological changes involve the modification of glutamatergic pathways in one way or the other. Different stages of neuroplasticity in brain circuits and cell function are described by Kalivas and O’ Brien [1]. Conscious decision-making is converted into poor decision-making by the use of drugs. Glutamatergic receptors participate in addiction-related metaplasticity [2]. Addictive drugs critically impact glutamatergic transmission in the hippocampus, medial thalamus, and prefrontal cortex. Treatment of addiction is challenged by the phenomenon of compulsive relapse. Patterns of remission and relapse in obsessive-compulsive disorder (OCD) are discussed by Eisen et al. [3]. Investigations carried out by these researchers led to the conclusion that complete remission is difficult to achieve.
A mathematical theory of reward based on the free-energy principle is presented below.
A Mathematical Theory of Reward
The Free Energy Principle
Free energy is the amount of energy available to do work in a system at constant temperature and pressure.
Entropy is the measure of disorder (randomness) in a system. It can be regarded as an amount of thermal energy per unit temperature that cannot be converted into useful work. At this point, ask a question:
Is Reward Necessary to Explain Adaptive Behavior?
Free-energy formulation of inference and learning schemes based on generative models of the world has been discussed in literature [4, 5]. In this chapter, our goal is to generate an understanding of optimal control theory in terms of the free-energy principle.
Optimal Control Theory And Free-energy Principle
Ensemble Dynamics, Reinforcement Learning and Optimal Control
Control is the expected action in a hidden state. Action a:M×S→A depends on the sensory states. It depends on internal and sensory states, hence on hidden states and random fluctuations in the past. Controlled flow is a policy that describes motion through state space. Policies represented by equations of motion that converge on attractors in state space, which are determined by a cost function, are used.
Selective destruction of stable fixed - points in costly regimes of state space
Sensory Samples
Policy is the flow under expected action. Applying ideas from statistical physics in the free-energy formula and approach of random dynamical systems, Friston and Ao [6] analyzed actions in terms of minimizing “sensory surprise”. An agent optimizes policy to maximize future rewards
