Dendritic Spines

Certain dendrites possess fingerlike extensions, 1-2 mm in length, called dendritic spines. In low magnification images, a high density of dendritic spines gives dendrites a fuzzy appearance (Figs. 1 and 2). Spiny protrusions are also found on the cell soma and on the axon initial segment, but the dendritic spines are more numerous and have received the most study. Neurons that have large numbers of spines on their dendrites are referred to as spiny neurons, whereas those with smooth dendrites...

John C Mazziotta

Disorders of the human nervous system are among the most debilitating and devastating of all human illnesses. Such disorders not only affect the physical abilities of patients but often severely compromise the quality of life, the ability to function in society, family relations, and the ability to maintain gainful employment. As such, neurological, neurosurgical, and psychiatric disorders affect not only the patients but also their families and society at large because of the tremendous...

Gaba And Disease

Defects in GABA synthesis, release, and response have serious consequences. Since GABA is a ubiquitous neurotransmitter, it can be argued that it has a role (direct or indirect) in most neurological diseases. The direct loss of GABAergic neurons in the striatum, for instance, is a hallmark of Huntington's disease. Parkinson's disease, however, results from a loss of dopamine neurons in the substantia nigra. The lost neurons normally project to GABA neurons in the striatum, and those lost...

Pupillary Light Reflex

The preceding connections permit a modern understanding of the pupillary light reflex. Light shone in one eye (e.g., the right eye) is conducted via the right optic nerve to both sides of the pretectum after crossing in the optic chiasm. The pretectal olivary nuclei on each side will then receive a neural signal related to the brightness of the light shone in one eye. This signal is relayed by each pretectal nucleus to both Edinger-Westphal nuclei. As a result there is a crossing at the chiasm...

Movement Disorders

Movement disorders involve abnormal, insufficient, or excessive motor activity. Most of the movement disorders involve stiffness, rigidity, bradykinesia (slow movements), tremors, tics, gait difficulties, and loss of control of movements. The most common movement disorder in neurology is Parkinson's disease, which is by far the most studied and well-understood. Other conditions include Tourette's syndrome, tremors, and myoclonus. Parkinson's disease is characterized by resting tremor (a tremor...

General Intellectual Ability

Determination of an individual's level of intellectual functioning is a fundamental component of the neuropsychological assessment. Once established, general level of intelligence serves as a point of reference from which to evaluate performance in other domains. Intelligence encompasses a broad range of capacities, many of which are not directly assessed in the traditional clinical setting. The estimate of general intellectual ability is based on both formal assessment methods and a survey of...

Emotional Affect versus Cognitive Processing Load

A unique strength of functional brain imaging is the ability to test various intuitions and hypotheses about our mental activities by virtue of the quantitative nature of the MR signal changes. Sometimes the most salient aspect of a stimulus (such as its emotional valence) may be less cognitively engaging than the lack of that cue. Specifically, although the localization of function repeatedly found in studies of the low-level aspects of sensory processing appears to have analogs in other...

Integrative Agnosia

Lissauer's dichotomy makes provision for two main stages of processing, apperception and association. Object recognition, however, involves more than matching stimuli coded in terms of primitive features such as line orientation to stored knowledge. Instead, the spatial relations between the lines and features need to be coded, the object needs to be segregated from its ground, and parts of an object need to be related and integrated. These processes are typically thought of as serving...

Cerebellum and Writing

Support for the hypothesis that the cerebellum is a cognitive controller outside the main cognitive processor but necessary for intermodule coordination derives from the observation that cerebellar patients can develop peripheral afferent dysgraphia. According to recent theories on the dysgraphias, peripheral afferent dysgraphia is characterized by two different groups of deficits. The first group, the so-called neglect-related features, is characterized by the tendency to write on the...

Mechanisms Operative in the Developing Brain

Many efforts during the past two decades to develop a suitable animal model for studying FAS met with only limited success. Microencephaly (reduced brain mass) is a characteristic finding in FAE FAS victims, and it was demonstrated that exposure of immature rodents to ethanol in late gestation or during the first two postnatal weeks caused a reduction in brain mass. However, numerous additional animal studies failed to provide an explanation for the reduced brain mass. A modest loss of neurons...

Islet Localization Of Neuropeptides

Immunocytochemistry has revealed three neuropeptides to presumably parasympathetic nerve terminals in pancreatic ganglia and in islets gastrin releasing peptide (GRP), vasoactive intestinal peptide (VIP), and pituitary adenylate cyclase activating polypeptide (PACAP). These neuropeptides are released from the pancreas upon electrical vagal activation and they stimulate both insulin and glucagon secretion, as demonstrated in a number of studies in vivo as well as in vitro. From both a...

Nucleus Basalis Of Meynert And Nucleus Of The Diagonal Band Of Broca

These nuclei consist of scattered groups of large cells in the basal part of the cerebral hemisphere, just ventral to the anterior commissure and the globus pallidus. The nucleus basalis (Figs. 2 and 3) is most prominent at the level of the anterior commissure, but some of its cell clusters extend caudolaterally toward the amygdala and dorsally around the edges of the globus pallidus. The diagonal band nuclei extend medially and dorsally (diagonally) into the septum. Because many of the cells...

Synthesis The HERA Model and Its Extension

Stable differences appear to exist in the activations accompanying encoding versus retrieval. The most striking pattern is in the activity of the prefrontal cortex. Most studies of encoding have shown activity in the left prefrontal cortex at a more anterior site, whereas most studies of retrieval have shown activity in the right prefrontal cortex, also at a more anterior site. This hemispheric difference in prefrontal activity in episodic memory is typically referred to as the Hemispheric...

Serotonin

Reserpine, an antihypertensive drug used in the 1950s and 1960s, depletes noradrenaline as well as serotonin and dopamine and frequently led to depression in patients who took this medication. This finding led to the hypothesis that mood disorders were caused by depletions of serotonin and dopamine. Serotonin (5-HT) is produced by the dorsal and median raphe located in the brain stem. The dorsal raphe sends projections to the frontal lobe, amygdala, hypothalamus, and basal ganglia, whereas the...

Laterality Across The Life Span

The various functional aspects of laterality correlate with each other weakly or not at all. This is inconsistent with the hypothesis that there is but one fundamental processing dimension along which the hemispheres differ and from which all laterality effects are derived. Consequently, laterality is unlikely to be determined by any single developmental influence. Instead, the relative independence of different manifestations of laterality indicates that there are probably several different...

Gkknd Wkhnitq

Figure 3 Schematic representation of the VIP gene and proVIP. The first exon is non-encoding, exon 2 encodes the signal peptide, exons 3-6 encode the proVIP sequence, and exon 7 is non-encoding. At the bottom of the figure are the amino acid sequences of VIP, glucagon, human PHM, secretin, and human GIP. * indicates a C-terminal NH2 group. exons. It encodes, besides for VIP, for peptide histidine methionine (PHM). This is a 27-residue peptide showing a high degree of homology to VIP because 15...

Cerebral Ischemia

In clinical practice, two general types of acute cerebral ischemia can be distinguished a focal and a global cerebral ischemia. Global cerebral ischemia is a result of cardiac arrest (i.e., following a collapse of the circulation) and leads to diffuse hypoxic brain damage. This is caused by various mechanisms that will not be discussed here. Disturbances in a supply area of a cerebral artery lead to focal perfusion deficits followed by an abrupt or ictal onset of focal or global neurologic...

Neuropeptide Y NPY

NPY was isolated from the porcine brain by using an assay developed by Dr. Tatemoto and Professor Mutt in 1982 to detect C-terminally a-amidated peptides. Because the isolated peptide was found to consist of tyrosine in both its N- and C-terminal ends, it was named NPY. The peptide consists of a 36-amino acid residue and shows a high structural homology to peptides YY (PYY) and PP. The human NPY gene is located on chromosome 7p15.11, consists of four exons, and encodes for the 29-residue signal...

Suggested Reading

I., Murray, L. S., and Scott, G. (1982). Diffuse axonal injury due to nonmissile head injury An analysis of 45 cases. Ann. Neurol. 12, 557-563. Adams, R. D., and Victor, M. (1999). Principles of Neurology, 6th ed. McGraw-Hill, New York. Caplan, L. R. (1995). Binswanger's disease Revisited. Neurology 45, 626-633. Del Bigio, M. D. (1993). Neuropathological changes caused by hydrocephalus. Acta Neuropathol. 85, 573-585. Edwards, M. K. (Ed.) (1993). Neuroimaging Clinics of...

Brain Reorganization

The brain can reorganize on the basis of the structures that remain after brain damage, possibly mobilizing mechanisms such as unmasking of previously present but relatively weak neural paths, neuronal sprouting, and the up- and downregulation of receptors at synaptic and nonsynaptic sites. Both human and animal studies have demonstrated mechanisms of brain plasticity and the reorganization of function following brain damage. A Science Research News article noted that a striking body of recent...

Mood Anxiety and Somatoform Disorders

The cooccurrence of migraine and psychiatric disorders has been studied extensively in several population-based and longitudinal surveys. Migraine is associated with both affective and anxiety disorders. Breslau and colleagues reported on the association of International Headache Society (IHS)-defined migraine with higher lifetime rates of affective disorder, anxiety disorder, illicit drug use disorder, and nicotine dependence. Migraine with aura was associated with an increased lifetime...

The Auditory System Of The Midbrain

The auditory system extends from the medulla to the telencephalon. Almost all parts of the auditory system are connected to the midbrain. The present treatment Encyclopedia of the Human Brain Volume 3 Copyright 2002, Elsevier Science (USA). Figure 1 Anatomy of the midbrain in drawings of transverse sections. (A) Caudal level of inferior colliculus and trochear nucleus. (B) Middle level showing the superior colliculus and oculomotor nucleus. (C) Rostral level of the posterior commissure and...

Chronic Lyme Encephalopathy

Figure 1 Representative MRI scan (left), SPECT image (center), and superimposed MRI SPECT image (right) in a normal subject and in a patient with objective evidence of LE. The dark areas correspond to lower and the light areas to higher perfusion. (See color insert in Volume 1). deficits described previously. Unfortunately, hypoperfusion in these brain regions is not specific to Lyme disease. Similar SPECT findings have been reported in other conditions that have symptoms similar to LE, such as...

Somatosensory Deafferentiation

An impressive illustration of the importance of somatosensory proprioception for motor control was provided by two patients who lost all proprioceptive afferences from the body up to the neck as a sequel of peripheral nerve diseases. The most dramatic symptom of complete sensory loss was an inability to make purposeful movements. Lacking somatosensory information about the actual position of moving limbs, the patients produced ill-oriented and ineffective movements of inappropriate strength....

Forward Modeling

For electrical or magnetic measurements at a distance significantly larger than the extent of the source, the spatial fine structure of the field distribution is not detected, and the dominant contribution is the dipole associated with longitudinal intracellular currents. In MEG, the effects of ohmic currents through the head volume are minimal, and a reasonable analytical solution can be derived by treating the head as a homogeneous conducting sphere. The radius of the sphere is chosen to...

Role of Experience in Development

The role of sensory experience during sensitive periods has been documented in numerous animal studies. Experience in part controls the selection of axons, dendrites, synapses, and neurons that will form the functional neural circuits. For example, during the sensitive period for ocular dominance, visual deprivation induced by monocular eyelid suture results in shrinkage of the ocular dominance columns serving the closed eye. Outside the sensitive period, visual deprivation has little effect on...

Fossil Brains Revisited

From the history of the brain in fish, amphibians, and reptiles as available from the fossil record, the most unusual inference is that these can all be treated as lower vertebrates in encephalization (Fig. 5). The exceptions are sharks and, perhaps, the ostrich-like dinosaurs (ornithomimids). Here is a list of a few more outstanding discoveries. First, from the evidence of small (< 15 cm long) Carboniferous (350 Ma) fossil fish, the diversity in living teleosts was probably foreshadowed by...

Clinical Evaluation and Management

Imaging with cranial CT or MRI can be useful in metabolic coma to differentiate between an ischemic infarct, an intracerebral hemorrhage, and a mass lesion involving the cortex or the brain stem. However, these imaging studies are often unremarkable during metabolic coma. Patients in coma who present with cranial nerve deficits and posturing likely suffer from a mass lesion involving the cortex or the brain stem. However, patients in coma with unilateral masses may not initially suffer from...

Telencephalon

Two large parts of the telencephalon have important roles in motor control the cerebral cortex and the basal ganglia. Of course, the function of both structures extends beyond motor control, but this article addresses only that role. a. Cerebral Cortex The number of functionally distinct motor cortical fields remains unknown. One heuristically useful view of the frontal cortex divides it into three main parts the primary motor cortex, a group of areas collectively known as nonprimary motor...

Evolution Of Laterality

The seeds of laterality were sown in our distant evolutionary past and may even be related to asymmetry in the molecules and particles of which all living things are constructed. Here, I outline a plausible scenario for the evolutionary emergence of human laterality. Although accounts of evolution remain speculative and difficult to test, the following scenario is built on what has already been said about laterality across species and on more detailed discussions of evolutionary considerations...

History

The previously mentioned observations, specifically that of the sheer size of the fiber tract and its position as a unique midline structure, were important in suggesting to early scientists that it would be crucial to understand the callosum's role in behavior to fully understand the organization of the brain. In the early literature, it even competed with the pineal gland as a potential seat of the soul. Responding to an increasing belief that the corpus callosum played a major role in the...

Learning And Memory As An Information Processing System

In the morning an employee arrives to work and realizes that her usual parking spot is taken. She parks in another parking area, but before she leaves she inspects the area looking for landmarks that will help her find her parked car at the end of the day. At the end of the day she searches for her car in the parking lot by looking for specific landmarks. The ability to find the location of the car by searching for landmarks is possible because the person makes an association between the...

Short and Long Term Memory

In 1890, William James distinguished between memory that endured for a very brief time and memory that lasted after the experience had been dropped from consciousness. The former, known as short-term (or primary) memory, refers to one's ability to recall material immediately after it is presented or following uninterrupted rehearsal. The latter, known as long-term (or secondary) memory, refers to the ability to remember information at a later time without the need for intervening rehearsal....

The hindbrain or rhombencephalon is an embryological

Term denoting the caudalmost of the three primary embryonic brain vesicles that form in the rostral neural tube. It gives rise to the pons and medulla oblongata as well as the greater portion of the cerebellum. Here, we restrict our view of the hindbrain to that region encompassing the pontine and medullary divisions since the cerebellum is discussed in a separate article. The pons and medulla oblongata are complex anatomical structures that subserve a wide range of vital functions. This...

Types Of Central Alexia A Pure Alexia

The syndrome of pure alexia was first described in the 19th century. The most striking feature of this reading disorder is that the patient retains the ability to write and spell thus, pure alexia is also known as alexia without agraphia. Patients who have alexia without agraphia cannot read that which they have just written. A characteristic feature of pure alexia is that patients with this form of alexia retain the ability to recognize words that are spelled aloud to them. That is, although...

Stress And Onset

Stress does not appear to be a major factor in explaining why individuals develop a bipolar disorder. Additionally, research does not support the idea that the number of depressive or manic episodes experienced by a patient relates to that individual's pre-onset stress level. There is also little or no scientific evidence that bipolar episodes are related to stress through the brain's kindling process. Kindling refers to the brain at the cellular level learning from repeated episodes to...

Brain Vein Images

Brain Vein

Stroke is characterized by the acute onset of a focal neurological deficit referable to an insult of the cerebral vascular system. Stroke is the third leading cause of death in the United States. There are approximately 500,000 new strokes each year causing 200,000 deaths. Many patients have significant functional impairment and require long-term medical or rehabilitative care, thus adding to the socioeconomic impact of stroke. Risk factors for the development of stroke include hypertension,...

Plasticity in Response to Music Perception

In the previous section, I discussed changes that may occur in auditory cortex as a result of long-term exposure to auditory feedback during music production. Generalized changes within the brain may also result simply from exposure to music perception. The duration of exposure varies significantly across studies. In an influential study, Greg Recanzone, Christoph Schreiner, and Michael Merzenich trained monkeys to make pitch discriminations within particular frequency ranges over several...

Imitation of Meaningless Gestures

Defective imitation of meaningless gestures has traditionally been considered a symptom of apraxia. Other symptoms of apraxia are disturbed production and imitation of meaningful gestures, such as waving goodbye or miming the use of a hammer, and disturbed use of real objects. However, there are, patients with pure visuoimitative apraxia'' in whom defective imitation of meaningless gestures contrasts with preserved production and imitation of meaningful gestures and object use. It thus seems...

C EEG Activities of the Limbic Cortex

Two main types of rhythmic EEG activities can be recorded from limbic cortical areas characterized by different dominant rhythmic components, one in the theta and one in the beta gamma frequency range. The former was first described by Green and Arduini in 1954, and in several species it may cover the frequency range between 4 and 12 Hz. It is common practice to call this activity theta rhythm since in most species it is dominant between 4 and 7.5 Hz however, since in rodents it can extend to...

Diencephalon

The diencephalon consists of four structures located deep in the cerebral hemispheres just rostral to the midbrain and surrounding the third ventricle the thalamus, hypothalamus, subthalamus, and epithala-mus. Despite its small size, the diencephalon has major importance in brain function, particularly through the activities of the thalamus and hypothalamus. The subthalamus is a very small region inferior to the thalamus that contains the subthalamic nucleus and zona incerta these areas have...

Psychogenic Stimuli

Fear or disgust at the sight, smell, or taste of something intensely disagreeable can precipitate nausea or even vomiting. The stimuli arising in the visual, olfactory, or gustatory receptors are finally relayed to the cortical and limbic systems, which interpret and give meaning to the experience. In addition, anxiety itself is well-known to predispose one to nausea and vomiting. Also, higher functions in the brain can learn or be conditioned to respond with emesis to specific triggers. This...

Feature Analysis in Inferior Temporal Cortex

As noted earlier, the pattern of receptor firing rates on the retina constitutes the initial representation of an object. In a like manner, the center-surround ganglion cells and simple and complex cells in V1 can be considered increasingly complex object representations, with each cell coding for a particular feature (e.g., an edge tilted at a particular orientation) of the object. How are objects represented in later visual cortical areas Axons from neurons in V1 project to several other...

Studies Of Multisensory Integration In Human Cortex

In the past few years there have been a number of studies exploring the neural bases of multisensory integration in human cortex. Initially, such studies utilized event-related potential (ERP) recording techniques in which the averaged responses of thousands of neurons are recorded from surface electrodes on the scalp. The temporal resolution of ERP recordings is excellent (events can be measured in milliseconds) and can easily be combined with conventional behavioral or perceptual measures in...

The Genetics Of Handedness

Given the evidence that handedness patterns in humans extend far back into evolutionary history, it is not surprising that the vast majority of theories of handedness have included the suggestion of a genetic factor. There have been a number of studies that have examined handedness in families in order to verify this hypothesis. Unfortunately, the empirical evidence on handedness does not strongly support genetic theories. There is a fairly consistent finding that left-handedness is more likely...

Peripheral Motor System 1 Muscles

Skeletal muscles consist of specialized cells, which fuse during development to form fibers (technically, a syncitium). There are two types of muscle fibers Encyclopedia of the Human Brain Volume 3 extrafusal and intrafusal. Extrafusal fibers, which attach to tendons and then to the skeleton, produce force and movement. Intrafusal fibers, which contain muscle spindles, attach to muscles and serve a sensory function. Force and movement depend on muscle proteins, principally myosin and actin,...

Preface

The functions of the human brain are the last major challenge to science. Despite having made rapid strides in understanding the cosmos, subatomic particles, molecular biology, and genetics, we still know very little about the organ that made these discoveries possible. How does the activity of 100 billion nerve cells mere wisps of protoplasm that constitute the brain give rise to the broad spectrum of abilities that we call consciousness, mind, and human nature There is now, more than ever...

The Parasympathetic Branch Of The Autonomic Nervous System

Until relatively recently, little attention in biofeedback has been given to the other branch of the ANS, the parasympathetic branch (PNS). Activity from this system is difficult to measure, and it was thought that the sympathetic system was the dominant contributor to stress. However, the evidence to support this idea has not been found. It is difficult to verify sympathetic overdrive'' in the disorders listed earlier. In fact, most patients with functional disorders do not appear to be in...

Glossary

Antigen presentation Presentation of processed antigens on the surface of macrophages, microglia, or dendritic cells concomitant with major histocompatibility complex class II molecules is a mandatory step for generation and activation of antigen-specific T cells. cytokine Soluble factor regulating interactions between immune cells. glia Nonneuronal cells of the central nervous system encompassing microglia, astrocytes, and oligodendrocytes. major histocompatibility complex Immunological...

Mechanism of Rapid Synaptic Transmission

Arrival of an action potential at an axon terminal causes voltage-gated ion channels to open, thereby allowing Ca2+ ions to enter the terminal. Within 100 msec, their presence triggers quantal release of neurotransmitter into the synaptic cleft by exocytosis Figure 29 Chemical synapse an axon terminal typically shows a few neurofilaments, many mitochondria, and numerous synaptic vesicles. These spherical organelles, unique to neurons, are found attached to the actin cytoskeleton in relatively...

Microscopic Anatomy

As indicated earlier, the brain contains extraordinary numbers of neurons and glial cells. The remarkable capacities of the brain result in part from the wealth of neurons and their connections, and the glia provide important support for the optimal function of the neuronal population. In this section, we consider microscopic aspects of the major cell types in the brain. The neuron is the fundamental functional unit of the nervous system. Neurons are anatomically specialized to transmit...

Tensiontype Headache

Tension-type headache was previously known by several terms muscle contraction headache, stress headache, ordinary headache, essential headache, psychogenic headache, or psychomyogenic headache. It is defined as recurrent episodes of headache lasting minutes to days. There are two primary forms episodic and chronic. The pain is bilateral, with pressing or tightening (nonpulsating) quality of mild-to-moderate severity. The headache is not aggravated by routine physical activity. Photophobia or...

The Immune System as a Sensory Organ

The phenomenon of sickness behavior illustrates that the immune system may be considered as another sensory organ of the body. Following this definition, the immune system's function is to detect noncogni-tive stimuli,'' such as bacteria, viruses, and tumors, and to alert the CNS of their presence. The immune system has particular receptors (or, in this case, different types of cells) that detect specific stimuli, produce signals that can be understood by the CNS, and transmit messages to the...

Neurotransmitter Transporters and Receptors 1 Glutamate Transporters

L-Glutamate is the major excitatory neurotransmitter in mammalian CNS. High-affinity glutamate transporters are believed to be essential both for terminat ing synaptic transmission and for keeping the extracellular glutamate concentration below neurotoxic levels. Many glutamate transporter subtypes are known and may display different functions in different neural subtypes. GLT-1 and GLAST transporter subtypes were shown to be selective markers of all astrocytic plasma membranes. GLAST...

Social Decision Heuristics

Decision-making mechanisms can exploit the structure of information in the environment to arrive at better outcomes. The most important aspects of an agent's environment are often created by the other agents with which it interacts. Two of the key problems social agents face are the questions of how to (fairly) divide up resources among one another and how to make cooperative decisions in situations in which the pursuit of self-interest by each agent would lead to a poor outcome for all. We...

Disorders Involving Medical Intervention 1 Neoplasms

Perhaps primary among such disorders would be neoplasms or tumors, because early detection and intervention can have crucial implications. Whereas primary brain tumors do not typically occur with high frequency in a pediatric population, neuropsychologi-cal assessment can detect them at an early stage, frequently before the child would be referred for computerized tomography or other radiological procedures. This is due to the fact that neuropsychological assessment measures functional...

Disorders of Reading Single Words

The contemporary study of acquired dyslexias has largely focused on impairments in the ability to read single words aloud. One model of the mechanisms involved in reading a word aloud claims that there are three separate and partially independent routines in the brain for converting a written word into its spoken form The first pathway (the semantic route) involves recognizing a word visually, gaining access to its meaning, and then activating the sound of the word from its meaning. The second...

Defects in GAD

Autoimmunity to GAD is a hallmark of two related conditions insulin-dependent diabetes mellitus (IDDM, juvenile diabetes, or type 1 diabetes) and a rare neurological disorder called stiff-man syndrome (SMS). IDDM is an autoimmune disease in which T cells mistakenly destroy pancreatic b cells, which are the sole producers of insulin. Several b cell proteins are targets of autoantibodies, including GAD65, GAD67, and insulin. These autoantibodies often arise several years before disease onset,...

Host Immune Response

Another potentially serious limiting factor in graft survival, despite optimal in vitro tissue processing and efficient implantation protocol, is host rejection of the graft. Whereas the brain is still considered to be an organ with a limited immue response (historically called immunoprivileged), rejections of grafted tissues can occur through the classic cell-mediated immune response. The immune reactions to neural grafts have been studied for a long time, but the necessity of immune...

Dementia with Lewy Bodies DLB

In addition to occurring in brain stem structures in persons with PD, Lewy bodies are the neuropatho-logical characteristic of DLB, where they appear diffusely distributed throughout the neocortex, diencephalon, brain stem, and basal ganglia. Because of the brain structures involved, DLB is sometimes considered to be among the frontal-subcortical dementias. The core clinical features of DLB are the presence of dementia, gait-balance disorder, prominent hallucinations and delusions, sensitivity...

Evolution Of The Motor System

The motor system was born, not made, and many of the characteristics of the human motor system reflect its history. The CNS's chief function involves the acquisition of a behavioral repertoire, which can be stored both genetically and epigenetically, and the selection from that repertoire of the actions most likely to enhance an individual's fitness, in the inclusive sense of that term. It seems likely that the ability to move in a goal-directed manner developed in an invertebrate ancestor of...

Typical Patterns of Results

Implicit Explicit Memory Brain

As discussed previously, researchers generally conceptualize memory as having three stages (encoding, storage, and retrieval). The types of strategies that people use during the encoding (or acquisition) stage have a profound effect on what is remembered at a later time. Considered here are just a few of the classic variables shown to strongly affect performance on a later memory test. The level-of-processing effect is one of the most robust and well-known findings in the explicit memory...

History Of Mental Retardation

There is a long history of persons with mental retardation that dates back to antiquity. In general, the view of persons with mental retardation varied based on accompanying social, political, and religious beliefs. Earliest recordings of mental retardation are found at approximately 1500 bc from ancient Egypt. These recordings refer to those whom we would distinguish as persons with mental retardation as being inferior, needing to be separate from society, and having the real possibility of...

Topographic Mapping Of Human Visual Cortical Areas

Functional magnetic resonance imaging (fMRI) has been used to map the location, extent, and topographic organizations of several cortical areas in the human visual system. Signals used by fMRI are thought to represent local changes in blood flow that serve as an indirect marker for the activation of pools of neurons. Eccentricity and polar angle coordinates in several visual areas (V1, V2, V3, VP, and V3A) are usually mapped using phase-encoded, contrast-reversing checkerboard stimuli that were...

Benign Autoimmunity

The mammalian immune system is composed of two classes of elements innate and adaptive. The innate arm of the immune system is encoded in the germline of the species and is inherited by the individual from his or her parents. Innate immunity includes the macrophages, neutrophils, and other inflammatory cells and molecules. The adaptive arm of the immune system contains the T cells and the B cells, which express antigen receptors that are somatically generated in each individual. Activated B...

Motoric Working Memory Imagery

As many musicians have discovered, musical instrument playing can be rehearsed mentally. For example, in the piano keyboard melody recall task described previously, the pianists reported mentally rehearsing their keyboard recall attempts, not only through inner singing but also through mental simulation of keyboard fingering, prior to actually playing. To investigate the effects of mental practice, Pascual-Leone, in the piano keyboard sequence learning experiment described previously, also...

Locus Ceruleus Efferent Fibers Innervate Many Target Structures

A striking feature of the LC is the extreme divergence of its projections, partly due to an intense collater-alization of the axons. Indeed, a few neurons (20,000 in humans and 1,500 in rats) provide extensive innervation of the brain from the olfactory tubercle to the spinal cord (Fig. 1). Projections of the LC are organized in two ascending fiber systems first, the dorsal NE bundle innervating the amygdala, olfactory tubercle, septum, bed nucleus of the stria terminals, hippocampus, entire...

The Autonomic Nervous System

The autonomic nervous system is primarily an effector system that innervates smooth musculature, heart muscle, and exocrine glands. It is a visceral and largely involuntary motor system. Anatomical principles underlying the organization of both somatic motor and autonomic nervous systems are similar (Fig. 4) and the two systems function in parallel to adjust the body to environmental changes. Nevertheless, the two systems differ in several ways. Within the autonomic nervous system, two...

Recent Studies of Crossed Aphasia in Bilinguals

Three studies meet at least the first two of these criteria. The first study, by Nair and Virmani, examined the incidence of aphasia following right- and left-sided lesions in a large group sample of hemiplegics, many of whom were polyglot, presenting at the researchers' clinic. Although a rather high incidence of aphasia following right-sided lesions was noted (12 24 right handers), a separate breakdown of the relative incidence of crossed aphasia in the polyglots versus the monolinguals in...

Dissociation and Conversion

The term dissociation originated in the 19th-century work of Pierre Janet, who proposed one of the earliest systematic accounts of the psychopathological mechanisms underlying somatoform phenomena. Although more than a century old, many of Janet's ideas concerning the organization of mental processes remain popular (albeit implicitly) within contemporary cognitive psychology. According to Janet, personal knowledge is represented by an integrated network of associated memories, which are...

What Is Behavioral Pharmacology

Subjects commonly studied in behavioral pharmacology are people, monkeys, rats, and mice, with rats probably the most studied, but the study of mice is increasing. Larger animals may be required when surgical interventions or electrode implantation in brain are part of the study otherwise, smaller animals such as mice are easier to house and work with, cheaper, can be studied in larger numbers, and are genetically more homogeneous. The methods of behavioral pharmacology are numerous and varied....

Behavioral Treatment

Pharmacological treatments of epilepsy are not uniformly successful. Even if good seizure control is obtained, many patients experience troublesome side effects of treatments that must often be continued for many years. The need to take medication on a long-term basis has obvious implications for women wishing to become pregnant. In addition, many individuals describe feelings of oppression and an increased fear of being labeled as ill because of their ongoing need for regular drug taking....

Motor Neurons and Motor Units

In the ventral part of the spinal cord, motor neurons are organized into segregated motor pools, which innervate particular muscles. Alpha motor neurons send their axons from the spinal gray matter to terminate on extrafusal muscle fibers. Gamma motor neurons send their axons to intrafusal muscle fibers. Motor pools extend over two to four spinal segments, with medially situated motor pools innervating axial muscles (e.g., those of the neck and spine). Laterally situated motor pools project to...

Preventive Treatment

Preventive treatment is administered on a daily basis to decrease the frequency and lessen the severity of the attacks. Indications for preventive treatment include the presence of disorders such as hemiplegic migraine, recurrent migraine attacks that significantly interfere with daily function despite acute treatment attacks that occur more than twice a week, or acute treatment that is not satisfactory is excessive, or contraindicated. Maximum benefit may take 3 months. If effective,...

Energy Metabolism Of The Developing Brain

Much like the changes in lipid and protein compositions described earlier, energy metabolism of the brain also undergoes an interesting shift during development. The most dramatic of these changes are changes in blood flow and oxygen consumption and the utilization of glucose as the source of energy. It is well-known from both in vitro and in vivo studies that oxygen consumption by the cerebrum remains at a low level at birth, although oxygen supply to the tissue may be high. Investigations...

Visual Field Topography

Traditionally, visual field topography has been a primary source of information used to identify and map different visual areas in animals. Early work showed that a number of cortical visual areas contain a complete representation of the visual field, though each representation is split along the vertical meridian so that half of the field is represented in each hemisphere. Generally, then, the topographic arrangement of photoreceptors in the retina is maintained in the central connections....

The Evidence A Fossil Brains

The fossil record of the brain is from casts (''endo-casts'') that are molded by the cranial cavity of fossil skulls. Natural endocasts are made by the replacement of soft tissue in the skull by sand and other debris that eventually fossilizes. Artificial endocasts can be made by cleaning the cavity and filling it with a molding compound such as latex, from which plaster casts can be made. Errors in identifying brain areas in endocasts of birds and mammals are likely to be about the same as in...

The Dimensionality of Color Vision

Color vision has been frequently studied in laboratories by asking observers to judge whether pairs of stimuli typically viewed as the respective halves of a small, illuminated circle (Fig. 2) appear the same (''match'') or are different. If the two halves are identical in wavelength and intensity content, they of course match. Differences in color appearance may be introduced by changing the intensity or wavelength content of one half or by changing both these features. A change in the...

Structure Function and Reaction of Central Nervous System Cells to Injury

Neurons and their networks of axons, dendrites, and synaptic contacts are the basic elements for perception, conduction, and processing of information. They vary in shape and size and show different changes in Encyclopedia of the Human Brain Volume 1 Copyright 2002, Elsevier Science (USA). Overview of Pathogenetic and Clinical Aspects of Brain Lesions Viral (HSV, HIV) Fungal Parasitic Prions (CJD) Immunosuppressed patients Multiple sclerosis Cerebral ischemia Intracerebral haemorrhage Vascular...

Window On The Mind

Human electroencephalography (EEG) provides a convenient but often opaque window on the mind,'' allowing observations of electrical processes near the brain surface. The outer brain layer is the cerebral cortex, believed to be largely responsible for our individual thoughts, emotions, and behavior. Cortical processes involve electrical signals that change over times in the 0.01-sec range. EEG is the only widely available technology with sufficient temporal resolution to follow these quick...

Conclusion

Several theories have been proposed to describe LC functions, ranging from notions of reinforcement and arousal to the mediation of anxiety or the control of selective attention. Because there is a good chance that most of these theories, although different, originate from the same observations, it seems wise to restrict this conclusion to a brief description of experimental data that have reached general agreement. On an anatomical point, LC cells send widely ramifying axons, which innervate...

Historical Development

From the dawn of self-reflective thinking, humans have wondered about the source of mental activity. The solution to this puzzle was largely relegated to superstition, faith, and philosophy. The 137th Psalm (sixth century b.c.e.) may constitute one of the earliest recorded descriptions of a neurobehavioral syndrome If I forget thee, O Jerusalem, let my right hand forget her cunning. If I do not remember thee, let my tongue cleave to the roof of my mouth if I prefer not Jerusalem above my chief...

Case Studies

JW is a relatively young man, in his early forties, who, despite many preserved cognitive abilities, fails to recognize many common objects. In August 1992, JW suffered a severe cardiac event while exercising and was subsequently anoxic. A computed tomography (CT) scan revealed multiple hypodensities in both occipital lobes with minor hypodensities in his right parietal lobe. Although JW has normal visual acuity as well as intact color and motion perception, Behrmann and colleagues have shown...

Vagus Nerve

Cranial nerve X has five components and by this measure joins cranial nerve IX in the distinction of being most complex. It has three sensory components GSA, SVA, and GVA and two motor components GVE and SVE. The GSA component is a minor one its fibers innervate the region of the external auditory meatus and the tympanic membrane. These GSA fibers have cell bodies located in the superior (jugular) ganglion of X and enter the brain stem via the vagus nerve. They terminate in a rostrocaudally...

Components of Eye Movement Systems 1 Superior Colliculus SC

The superior colliculus forms the anterior roof of the midbrain (Fig. 1B). Its rostral border is the pretectum, and its caudal border is adjacent to the inferior Extrastriate visual cortex (occipital) Multimodal association cortex (parietal) Auditory association cortex (temporal) Somatosensory association cortex (postcentral) Premotor, motor, and oculomotor cortex (precentral) Prefrontal association cortex (frontal Diencephalon Hypothalamus Zona incerta Fields of Forel Thalmic nuclei reticular,...

Logical Reasoning and Personal Reasoning

Clinical studies in the early 20th century often reported the loss of ''abstract thinking'' as a result of brain damage. Such accounts, however, suffered from two irremediable problems. On the one hand, they never succeeded in characterizing a principled difference between abstract and concrete thinking. On the other hand, they failed to pin down the particular effects of lesions in different parts of the brain. This shortcoming is understandable given that many regions of the brain are likely...

Temporal Arteritis

Temporal arteritis is caused by an inflammatory process to the cranial arteries, and headache is the most common presenting complaint. It is also associated with night sweats, weight loss, aching of joints, low-grade fever, and jaw claudication. The headache pain is usually localized to the affected scalp vessels. Many patients will complain of pain on chewing. Temporal arteritis should be ruled out in any patient over the age of 50 who presents with an initial onset of headache and who was...

Heuristics for Multiple Alternative Choices

Not all choices in life are presented to us as convenient pairs of alternatives, of course. Often, we must choose between several alternatives, such as which restaurant to go to, which apartment to rent, or which stocks to buy. Table II lists various decision heuristics that have been proposed in the psychological literature for choosing one out of several alternatives, where each alternative is characterized by cue (or attribute) values and where the importance of a cue is specified by its...

The Sound Field A Sound

Any object that has inertia and elasticity can vibrate and as a consequence can produce sound. Vibrations have three main variables amplitude, frequency, and time. The simplest vibration is harmonic motion as described by a sinusoidal relationship between displacement and time shown in Fig. 1. Amplitude describes the distance through which a vibrating object travels, and it is related to intensity. Frequency is the inverse of Encyclopedia of the Human Brain Volume 1 Copyright 2002, Elsevier...

Introduction

Manic-depressive illness belongs to a spectrum of neurobiological diseases that today are most often called bipolar disorders. The terms are often used interchangeably in popular and scientific literature and refer to an interrelated group of illnesses rather than a Encyclopedia of the Human Brain Volume 2 Copyright 2002, Elsevier Science (USA). single disorder. The popular press and public speakers often use manic-depression and bipolar I disorder as synonyms for a single illness. This is...

Drugs of Abuse

The neurotoxicology of illicit drugs is not well understood in general. Drug abusers often abuse more than one agent, and it is difficult to determine the effects of one drug in isolation. There are examples, however, of relatively pure syndromes of impairment, and certain drugs have a known or putative effect on the cerebral white matter. a. Toluene This drug, methylbenzene, is an organic compound widely used in industry and is the major solvent found in spray paints. Occupational Figure 6 MRI...

Major Symptoms

The type of bipolar disorder a person has is largely determined by identifying the severity, number, type, and duration of manic and depressive symptoms the person has or is experiencing. Diagnosis of bipolar disorders is complicated by the fact that many symptoms of unipolar depression and manic-depression overlap. As an example, agitation and insomnia can occur in the depressed and in the manic state. Hypersomnia and psychomotor retardation, however, are observed more in bipolar than in...

Investigating The Aging Brain

The changes in the brain associated with aging are seemingly both evident and elusive. Obviously, aging continually takes place from conception to death, but in this article, we address only that aspect of aging associated with senescence. What is evident is that there is apparently a clear decline in numerous brain-mediated sensory, motor, and cognitive processes with advancing age, although what exactly declines is not fully understood. Likewise, the gross morphology of aged brains looks...

Participation Of The Hypothalamus And The Limbic System In Homeostasis

The internal environment of the body, a term embracing tissue fluids and organ functions such as blood pressure, heart rate, and respiration rate, is under the control of three independent processes. The auto-nomic nervous system plays an important role in homeostasis. Hence, in the brain, neurons that affect the activity of the preganglionic motor neurons of the sympathetic and the parasympathetic nervous systems are concentrated in the hypothalamus. The evidence is clear When the hypothalamus...

Cognition Beyond Psychology

The cognitive revolution in psychology was paralleled by the development of the field of cognitive science, whose practitioners included philosophers, linguists, computer scientists, neuroscientists, behavioral biologists, sociologists, anthropologists, and psychologists. In some sense, the rise of cognitive science may have been a reaction to the dominance of behaviorism within psychology Many who wished to pursue a science of mental life may have believed that they would have to go outside...

Implications For Rehabilitation From Brain Injury

Life is often unfair, or so it seems. Not surprisingly, people frequently become angry when confronted with life's inevitable misfortunes, including injury due to accident or disease. For example, a brain-injured patient suffering paralysis or aphasia following a stroke may, like any other patient, experience anger at the seeming unfairness of events. When the anger is misdirected at health care providers, not to mention friends and family, treatment may be disrupted and recovery prolonged....

The Aging Brain

The studies of brain and cognition reveal that in both domains, age-related changes are differential as well as generalized. The results of postmortem and in vivo investigations of the human brain demonstrate that although advanced age is associated with reduced total brain weight, nonspecific sulcal expansion, ventricular enlargement (Fig. 1), and a decline in global brain Figure 1 Examples of brain aging as seen on MR images (a 23-year-old female and a 77-year-old female). The images...

Sensorimotor Control Of Hand Movements In Object Manipulation

To understand and appreciate how the brain controls movements of the hand, it is best to study the natural behavior of the hand in everyday manipulatory tasks. During the past 20 years, the sensorimotor control of the hand in precision manipulation task has been investigated in great detail. In this section, we review what has been learned about the sensorimotor control of natural hand movements when grasping and manipulating objects with the fingertips. The remarkable manipulative skills of...

Cingulate Motor Cortex

Cingulate cortex along the medial wall of the cerebral hemisphere has traditionally been associated with the limbic system. The functionally significant subdivisions of cingulate cortex are not well established. Architectonically, the region is formed by two clearly distinct regions, areas 23 and 24 of Brodmann, with the more posterior granular area 23 having an obvious layer 4 and the more anterior agranular area 24 lacking a clear layer 4. Both areas are located ventral to the agranular...

Ventromedial Striatum Ventral Pallidum And Medial Thalamus

Although the ventromedial striatum, ventral pallidum, and medial thalamus are not part of the limbic system as traditionally defined, they have substantial connections with all the limbic structures discussed previously and are closely tied to them functionally. The amygdala, hippocampal formation, and the ventromedial prefrontal cortex all project onto the ventromedial part of the striatum, leading into a circuit that connects through the ventral pallidum to the mediodorsal thalamic nucleus...