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...

Neural Network Simulation

Computer simulation plays an important role in neural network research. It was not until fast and inexpensive digital computers were available that it became possible to study the behaviors of biologically detailed neural network models or large connectionist ANN networks. A variety of software-based simulators have been developed that enable researchers and students to more readily construct biological and artificial neural network models and evaluate their behavior and performance using...

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...

Introduction

It has long been known that there is some degree of localization of function in the human brain, as indicated by the effects of traumatic head injury. Work in the middle of the 20th century, notably the direct cortical stimulation of patients during neuro-surgery, suggested that the degree and specificity of such localization of function was far greater than had earlier been imagined. One problem with the data based on lesions and direct stimulation was that the work depended on the study of...

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...

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...

Principles Of Ion Channel Mechanisms A The Electrochemical Gradient

The electrochemical gradient determines the direction that ions will flow through an open ion channel and is a combination of two types of gradients a concentration gradient and an electrical field gradient. We can consider these two gradients separately. Figure 1a shows two compartments that contain an aqueous solution of ions separated by a membrane. It is apparent that there is a concentration gradient, since the left side contains more ions than the right. Assuming the membrane is permeable...

Organized Display of Inputs on Neurons

Each neuron has its view of the world, a spatial arrangement on its receptive surface of the inputs (many or few) impinging on it. The location of each input (on the dendritic tree, cell body, or initial region of the axon) indicates its source and helps to determine its efficacy in bringing about excitation, inhibition, or modulation of target cell activity. Figure 16 Dendrites electron micrographs (EMs) show that the CNS is a hypercomplex epithelium, with billions of pieces fitting together...

Vaid and Hull Meta Analysis 2001

Since the 1991 meta-analysis of Vaid and Hall, the literature on behavioral functional asymmetry in bilinguals has more than doubled. Many of the newer studies do not suffer from at least the more obvious methodological limitations that plagued the earlier studies, although it has also become clear that continued use of standard dichotic listening procedures may not be particularly informative. Many recent studies have begun to consider task-related processing differences in interaction with...

Abducens Nerve

Cranial nerve VI is one of the set of three ocular motor (oculomotor) nerves (III, IV, and VI) and innervates one of the six extraocular muscles of the eye, the lateral rectus muscle. The abducens nerve is a purely motor nerve with only a GSE component. The nerve arises from motor neurons in the abducens nucleus, which lies in a medial position in the dorsal pons and, along with the other oculomotor nuclei and the hypoglossal nucleus, forms the GSE column of the brain stem. Abducens nerve...

Olivocochlear Efferent System Central Modulation of Inner Ear Transduction

The cochlea, in addition to supplying afferent input to the brain stem, receives efferent projections that originate in the SOC. In animal studies it has been shown that two basic groups of brain stem neurons provide efferent innervation to the organ of Corti. Based on the general locations oftheir cell bodies in the SOC, they form the lateral (LOC) or medial (MOC) olivocochlear system. The LOC originates from AChE-positive neurons in and around the LSO and terminates primarily in the...

Neural Circuitry of Voluntary Saccades

The principal eye movement of the FS is the voluntary saccade. Humans average about two saccades sec while awake, and thus most of the day is spent in brief fixations of different parts of the visual world, continually interrupted by saccades. This incessant visuomotor activity, the processing of foveal visual data during a fixation, as well as the planning and execution of the next saccade, occupies much of the human brain, as exemplified by the expansive zones of

Natural Language Processing

Human language, which is generally recognized to be a phenomenon quite distinct from (and in advance of) any known animal communication mechanism, is often considered to be a characteristic feature of intelligence. The Turing Test for AI hinges on whether a computer system can communicate in natural language sufficiently well that a human observer is likely to mistake it for another person If so, then we must concede that the system exhibits AI. From this widely accepted viewpoint, natural...

Optic Aphasia

Like agnosic patients, patients with optic aphasia have a modality-specific (visual) recognition deficit and can recognize objects from both auditory and tactile presentation. The critical distinction between agnosia and optic aphasia, however, is that optic aphasic patients can recognize objects. This is evidenced by their nonverbal identifications (e.g., through gesture) and their ability to sort a visual stimulus with other stimuli of the same category. Additionally, these patients are also...

Learning Perceptual Skills

Research on the psychophysics of perceptual learning suggests that long-term learning of skills is not limited to motor areas. This research suggests three striking findings learning to detect a visual stimulus is specific to a retinal location, it only occurs if the stimulus is behaviorally relevant, and effects of learning remain robust after nearly 3 years without practice. Although there has been relatively little neuroima-ging research on perceptual learning, the research that has been...

Nuclei of the Posterior Commissure NPC

Five different cell groups of nuclei of the posterior commissure can be identified in the dorsal portion of the meso-diencephalic reticular formation (1) the principal part, (2) the magnocellular part, bordering the central gray medially and within the central gray itself, (3) rostral, (4) subcommissural, and (5) infra-commissural portion below the posterior commissure. The principal and magnocellular parts are the ones typically observed. The afferents to the nucleus of the posterior...

Sleepwake Cycles

According to sleep researcher Alan Hobson, ''Sleep is characterized by a recumbent posture, a raised threshold to sensory stimulation, decreased motor output and a unique behavior, dreaming.'' Sleep is, ironically, one of the least well-understood biological phenomena, yet over one third of our lives are spent in this behavioral state. Various hypotheses of sleep function and the functional significance of sleep have been proposed. These hypotheses have led to the development of a variety of...

The Cell Body

The neuronal cytoplasm is crowded by filamentous, membranous, and granular organelles arranged concentrically about the nucleus. Neurofibrils are best seen in large neurons, but are present in almost all (Fig. 21G). With metallic-impregnation, they are thin, interlacing, silver-loving threads (up to 2 mm in diameter) running through the cytoplasm and extending into dendrites and axon. With electron microscopy (EM), three kinds of filamentous structures are seen in neurons microfilaments...

Surgical Procedures A Selective Dorsal Rhizotomy

Selective dorsal rhizotomy (SDR) is a surgical procedure that involves severing specific sensory nerves that innervate the lower extremities. This selective dener-vation reduces abnormal excitatory peripheral sensory input to the spinal cord. Lumbosacral sensory nerves (L2-S2) are exposed and separated into component rootlets. These rootlets are then electrically stimulated and abnormal responses are recorded as well as visually observed. The rootlets producing abnormal responses are then...

Computational Capacities

Karen Wynn Sumas Restas

There is more to numerical knowledge than the ability to distinguish different numbers. The ability to distinguish numbers does not entail an ability to reason about those numbers, to determine, for example, that five is larger than three or that two is composed of one and one. To determine such relationships, the animal or infant must not only be able to construct mental representations of the relevant numbers but be able to manipulate these representations in numerically meaningful ways....

Multiple Intelligences

Gardner proposed that there is no single, unified intelligence but rather a set of relatively distinct, independent, and modular multiple intelligences. His theory of multiple intelligences (MI theory) originally proposed seven multiple intelligences linguistic, as used in reading a book or writing a poem logical-mathematical, as used in deriving a logical proof or solving a mathematical problem spatial, as used in fitting suitcases into the trunk of a car musical, as used in singing a song or...

Neuropsychological Model Of Number Processing

Triple Code Model

The abilities, performance patterns, and dissociations described in Section I, together with other findings relating to how human adults represent and process number, led the French cognitive neuroscientist Stanislas Dehaene to develop a cognitive neuropsychological model of number processing that is the dominant model today. In this model, our number knowledge consists of three distinct representational systems. Each of these systems represents numbers in a very different format from the...

Hemispheric Asymmetries In The Regulation Of Aggression

Several lines of neuropsychological research suggest differences in left and right hemisphere specialization for the processing of emotion, including anger and aggression. The left hemisphere plays a greater role in decoding linguistically conveyed emotional information, and the right hemisphere is more important in processing nonverbal emotional cues, such as prosody and facial expression of emotion. Moreover, the right hemisphere may be more highly specialized for mediating emotional...

The clinical syndrome of dementia is characterized by

Impairment of multiple cognitive functions (e.g., memory, language, visuospatial abilities, judgment), typically due to chronic or progressive brain disease. The cognitive impairments are frequently accompanied by personality changes, including deficits in motivation and emotional control. Several different illnesses can cause the dementia syndrome, and the pattern of cognitive deficits and personality changes may differ by the type of illness as well as by the specific brain structures and...

Pharmacological Studies

The effects of noradrenergic agonists and antagonists have been known for several decades, and many are now used clinically. Their major effects are observed at the periphery on the cardiovascular system, interfering with the NE released from sympathetic neurons. Due to their multiple sites of action, systemic administration of these agents sometimes led to difficulties of interpretation, and drugs had to be administered locally in brain structures. The effects of systemic administration of an...

Circuit Philosophy and Function

Figure 2 focuses on the relationships of the CS, US, CR, and UR pathways rather than emphasizing the physical position of the nuclei and tracts within the brain. Initially, in a naive subject, the CS does not cause a NM response. The US stimulates the trigem-inal nucleus, which then projects to motor nuclei to cause the reflexive UR from the first trial on. During training the interpositus nucleus receives convergent CS and US information. Eventually, this convergent information causes a change...

Physiology and Anatomy

Plasticity of Primary Sensory Cortex after Amputation Plasticity of somatotopic organization of primary sensory cortex (S1) in patients with phantoms after amputation of the lower arm and hand has been demonstrated by functional imaging with magnetoen-cephalography. The receptive fields of adjacent regions, devoted to the face on one side and to the upper arm on the other, invade the receptive field originally devoted to the hand. The parallel of remapping of sensations from face and stump to...

Motion And Color

So far, we have discussed the perception of motion defined by luminance. Motion can also be defined by another first-order property color. Human color perception is described by three technical terms hue, saturation, and luminance. In everyday usage the word color usually refers to the technical term hue (e.g., red, green, and blue), which is determined by the wavelength of light. Saturation measures how different the light is from white and quantifies the differences between white (zero...

Pathological Lefthandedness

Because simple genetic explanations for the existence of left-handedness do not seem to work, an alternate theoretical position has emerged. This begins with the suggestion that, although there are some natural lefthanders, right-handedness should be expected unless something unusual has occurred. Thus, although there is a genetically fixed bias toward right-handedness, and this implies some set of genes that determine handed-ness, in specific situations there might be partial penetrance (which...

Neurophysiology of Control

As with neuroanatomical studies of attentional control, there has been a substantial amount of research on single-neuron recordings from a range of brain areas. Those regions relevant to the biased competition framework are regions in the parietal and frontal lobes other important areas, such as the superior colliculus or pulvinar, will not be reviewed here. Many neurophysiological studies investigate overt spatial attention, in which the eyes overtly move to an attended location, in contrast...

Plasticity in the Language System after Brain Lesions

Studies of cerebral organization for language in the adult imply a greater role for perisylvian regions within the left hemisphere in language processing. This overall pattern appears ubiquitous in adults, and many investigators have suggested that the central role of the left hemisphere in language processing is strongly genetically determined. Certainly the fact that most individuals, regardless of the language they learn, display left hemisphere dominance for language in dicates that this...

Internal Models And Sensorimotor Integration

Adaptation can be thought of as belonging to an even broader class of motor learning phenomena termed sensorimotor integration. Although adaptation is restricted to a remapping of motor signals to sensory feedback, learning to track an object or move a mouse requires mapping particular sensory signals to sets of motor commands in a goal-dependent manner. These latter tasks differ from adaptation paradigms because these relationships involve unfamiliar sets of stimuli and responses. Prominent...

Other Forms of Migraine

Migraine with prolonged aura, perviously termed complicated or hemiplegic migraine, is characterized by one or more aura symptoms lasting more than 60 min and less than 1 week. Any of the various forms of aura may occur. This type of migraine is relatively rare. The headache usually starts within 1 hr of aura onset, becomes progressively more intense, and may linger for a prolonged period. Different forms of aura can be experienced at the same time. The intensity of the pain is usually less...

Conclusions

The human nervous system is similar in cellular elements, structure, function, and basic plan to the nervous systems of all vertebrates, especially those of its fellow mammals. This article has highlighted many organizing principles of the human nervous system anatomical pervasiveness, physical and functional coherence, centralized organization, structural specialization, use-designed components, phyletic uniformity with versatile adaptability, inherent plasticity, and recourse to chemical...

Motor Memory A Implicit and Explicit Memory Systems

The brain regions that store motor memories differ from those that store conscious memories. The former comprise an aspect of procedural memory or knowledge and the latter declarative memory or knowledge. Psychologists often refer to procedural knowledge as implicit memory and to declarative knowledge as explicit memory. Some psychologists use the term habit interchangeably for procedural knowledge, but this usage should not be confused with its biological meaning, which involves instinctive...

Touch Temperature and Pain

As noted earlier, the brain stem contains circuitry which subserves spinal cord functions'' for the head region. General sensation from the face and head region is mediated via trigeminal (cranial V) afferents with perikarya in the trigeminal ganglion. The central process of the trigeminal neuron enters the brain stem at the level of the ventrolateral pons. Myelinated afferents subserving light touch in the face and upper head region synapse in the principal sensory nucleus of V. Light touch...

General Features 1 Morphogenesis

The brain and spinal cord originate from the embryonic ectoderm through the action of inductive signals from underlying mesoderm and within the ectoderm. During this process, a region of dorsal ectoderm called the neural plate is delineated, folds together at the midline to form the neural tube, and invaginates into the dorsal aspect of the embryo. Even before closure and invagination of the neural tube are complete, three initial subdivisions of the brain can be discerned, first by the...

Cerebellum and Psychiatric Disorders

Various reports suggesting a possible link between the cerebellum and emotional behavior have been published since the beginning of the 20th century. However, these findings have been overshadowed by the generally accepted view of the cerebellum as a pure motor structure. In the 1970s, the convergence of pathological observations and experimental findings induced some groups to implant a cerebellar pacemaker to treat intractable behavioral disorders. Since then, data have been collected linking...

Cross Modal Coordination of Attention

The existence of attentional selection in different modalities raises a basic question Is there a single, supramodal attentional system that mediates selection across multiple modalities, or are there individual attentional systems for each modality that have some degree of cross talk with one another Results from neuropsychological patients with neglect support a supramodal view of attention. Neglect patients have difficulty attending to both visual and auditory stimuli opposite the lesioned...

Mri Signal Generation A The Nuclear Spin

MRI is based on the fact that collections of atomic nuclei, when placed in a strong unchanging magnetic field, interact with an externally applied oscillating magnetic field when the frequency of the oscillating magnetic field meets certain specific criteria. Many texts inaccurately summarize this by saying that atomic nuclei absorb or emit electromagnetic radiation (i.e., radio waves). It is not accurate to infer an interaction between atomic nuclei and electromagnetic radiation because...

The Premotor Cortex and SMA

Lying immediately rostral to the primary motor cortex is Brodmann's area 6. This secondary motor area is composed of two primary regions, the premotor cortex and SMA. Premotor cortex includes the lateral aspect of area 6, whereas SMA spans the medial aspect. Recent work has emphasized that there are likely many subareas within these areas for example, four distinct motor areas can be identified within SMA. Premotor cortex and SMA are well positioned to modulate motor output given their...

The Brain And Handedness

Control of the limbs, including the hands, is contra-laterally organized, meaning that the left hemisphere of the brain controls the right side of the body and the right hemisphere of the brain controls the left side of the body. In the 1860s, Paul Broca discovered that the major language production center in the brain is located in the left hemisphere of the brain. This center is now called Broca's area in his honor. There is another speech center called Wernicke's area that is associated with...

Other Specific Components of Astrocytes and Cells of the Astrocyte Lineage

Nestin is a protein the expression of which specifically distinguishes neuroepithelial stem cells (from which the name nestin originated) from other more differentiated cells in the neural tube. Nestin defines a distinct sixth class of intermediate filament protein, closely related to neurofilaments. Nestin is expressed by glial precursors such as radial glia and in the cerebellum by immature Bergmann fibers it is also expressed by adult Bergmann fibers recapitulating developmental stages when...

Auditory Working Memory Imagery

In a second condition of the same experiment, Zatorre and Samson presented patients with the same task, but with the retention interval filled by interfering tones. The right temporal lobe patients were impaired in this version of the task, regardless of whether Heschl's gyrus was involved. A group of patients with right frontal lobectomies were similarly impaired. Although the laterality of the frontal effect could not be assessed, the right temporal lobe effect was clear-cut and indicated a...

Degenerative Lesions

Use of the rubric of neurodegenerative disease is intended to cover a group of illnesses characterized by a progressive loss of neuronal populations in the CNS. In contrast to the defined metabolic, toxic, hypoxic-ischemic, or infective lesions described previously, the pathogenesis of neurodegenerative illness remains largely unknown. Some of these illnesses belong to the most frequent neurological entities and include Alzheimer's and Parkinson's disease. The affected neuronal populations in...

Nature And Nurture In Aggressive Behavior

Attempts to understand the brain basis of human aggression have often been thwarted by the outmoded dichotomies of nature versus nurture. Cultural and social influences are of critical importance in the genesis of human aggressive behavior. Violence may be motivated by the highest political and religious ideals and promoted and reinforced by cultural and governmental authorities. However, every violent behavior, whether springing from the most elevated or the basest of impulses, requires a...

Manganese

Occupational exposure to manganese (Mn) occurs among miners and welders. Frequently encountered organic Mn compounds include methylcyclopentadie-nylmanganese tricarbonyl (MMT), which is used as an antiknock additive in gasoline. Encephalopathy and basal ganglia dysfunction with parkinsonian signs including rigidity, gait abnormalities, dysarthria, hy-pomimia, and bradykinesia have been reported in patients with increased brain Mn levels due to chronic liver failure. The similarities between the...

Short Wavelength Cone System

The S cones are only involved in chromatic contrast, which has a lower spatial resolution than achromatic contrast. Chromatic aberration makes the short wavelength image out of focus when the image that the long-wave cone system sees is in focus. Therefore, the S cones have been excluded from high-resolution achromatic vision and the central fovea. S cones transmit their signals to the brain by a unique system of retinal ganglion cells. S cones synapse on S cone-specific on bipolars, which...

The Hypothalamus And Neuroendocrine Regulation

Neural regulation of pituitary secretion is one of the most important, well-characterized, and diverse functions of the hypothalamus. In fact, the demonstration that the hypothalamus exerts regulatory control over the pituitary is one of the landmark discoveries that tied the fields of neurobiology and endocrinology together. Recognition that hypothalamic control over the pituitary was humoral in nature resulted from structural studies that demonstrated a vascular link, or portal plexus,...

Structural Descriptions vs Views

By representing an object in terms of a limited number of high-level primitives and by explicitly specifying the qualitative relations between parts, structural descriptions are stable across many changes in viewing circumstances. For example, Fig. 4D shows the same object as Fig. 4A from a new viewpoint. Whereas the image (and thus any view-based representation) has changed, the same structural description should be generated. As noted earlier, such stable representations automatically solve...

Learning Sensory Motor Associations

What are strikingly missing from analyses of sequence learning, but apparent in other motor learning tasks, are changes in activation of the premotor and supplementary motor cortices. Studies of sequential finger tapping primarily require the learning of associations between movements that form a sequence. This kind of learning may be fundamentally different from learning that requires improvement in coordination or learning an altogether new motor movement. In addition, the finger-tapping task...

Eye Blink Conditioning

Eye-blink conditioning is perhaps the best studied model system for examining the neural basis of sensorimotor learning in mammals. In this form of Pavlovian conditioning, a neutral stimulus such as a tone is repeatedly paired with an aversive stimulus such as an airpuff to the eye. The airpuff is an unconditioned stimulus (US) It automatically elicits an unconditioned response (UR), either a blink in humans or the extension of a protective membrane in rabbits. Initially, the tone, or...

Attention and Executive Function 1 Attention

Many cognitive capacities are inherently predicated on a fundamental ability to attend to the surrounding The Wechsler Adult Intelligence Scale-III (WAIS-III) is composed of 13 individual subtests. Administration of all subtests generates three Intellectual Quotients (IQs) Full-Scale IQ, Verbal IQ and Performance IQ, and four different performance indices Verbal Comprehension Index, Perceptual Organization Index, Working Memory Index, and Processing Speed Index. Wechsler Intelligence Scales The...

Organic Amnesia

The most intensively studied of the organic memory disorders is the global organic amnesia syndrome, which was first characterized in the 19th century. In this syndrome, there is impaired recall and recognition of facts and episodes encountered both postmorbidly (anterograde amnesia) and (more variably) premor-bidly (retrograde amnesia). These deficits often occur even when intelligence and shortterm memory are preserved. There is also preservation of overlearned semantic memories, of various...

Internal Milieu

Figure 2 Functional zones of the cerebral cortex. store all the necessary information in stable memory traces. However, in the absence of access to information in other modalities, unimodal areas do not have the ability to lead from word to meaning, from physiognomy to facial recognition, or from isolated sensory events to coherent experiences. Such integration of sensation into cognition necessitates the participation of transmodal areas. The defining feature of a transmodal area is the...

Glossary

Prosencephalon Refers to the anteriormost major subdivision of the neural tube that gives rise to the forebrain. Consists of several major parts. The caudal part is the caudal diencephalon. The rostral part is the secondary prosencephalon this region consists of the telencephalic and optic vesicles, and the rostral diencephalon. prosomere Prosencephalic (forebrain) segment or neuromere. A transverse subdivision of the forebrain containing all the primary longitudinal subdivisions. rostral...

Individual Variation In Laterality

Thus far, I have emphasized contemporary human laterality patterns that could be considered prototypical, as if we were all more or less identical. Although there is sufficient homogeneity to justify consideration of the prototype, there is also sufficiently reliable heterogeneity to warrant consideration of individual variation. Of particular interest has been the possible relationship of functional hemispheric asymmetry to a number of other between-subject factors, including handedness, sex,...

Comparing the Basal Ganglia and the Cerebellum

In evaluating the role of the basal ganglia and cerebellum in skill learning, it is useful to compare these two prominent subcortical structures in terms of both anatomy and physiology. Although the neural circuits of each are unique, there are correspondences between the features of the cerebellum and basal ganglia that warrant a brief description. First, both form loop-like circuits in which inputs from the cortex are processed and then relayed back to the cortex via the thalamus. Second,...

Peripheral Dyslexias

A useful starting point in the discussion of acquired dyslexia is the distinction made by Shallice and Warrington between peripheral and central dys-lexias. The former are conditions characterized by a deficit in the processing of visual aspects of the stimulus that prevents the patient from reliably matching a familiar word to its stored visual form or visual word form. In contrast, central dyslexias reflect impairment to the deeper or higher reading functions by which visual word forms...

The Auditory Brain Stem And Auditory Cortex

The bilateral auditory neural pathway goes from the auditory nerve to the cochlear nucleus, the olivary complex, the inferior colliculus, the medial geniculate, and then the auditory cortex. There are numerous connections within and between these nuclei and from nuclei on one side of the brain to those on the other side. There is also a rich array of descending, efferent fibers that modulate the flow of neural information in the auditory pathway. The tonotopic organization seen in the auditory...

The Search For The Engram

The term engram is a hypothetical construct used to represent the physical processes and changes that constitute memory in the brain, and the search for the engram is the attempt to locate and identify that memory. Karl Lashley was perhaps the first person to clearly conceptualize the issue in a framework that would lend itself to experimental analysis. Lashley's primary interest was in localizing the engram to a specific region of the brain an endeavor that would prove to be extraordinarily...

Assessing Rehabilitation Potential

Who should be a candidate for cognitive rehabilitation Clinicians often confront a series of questions. For example, is the client out of a coma Is he or she medically stable and out of crisis What was his or her preinjury level of functioning What is his or her current level of functioning Are his or her perceptual skills intact Will he or she be able to attend to a therapist for any length of time and, if so, for how long Is the client combative, apathetic, depressed, or aggressive Are there...

Sensory Representations Maps

In all mammals, much of the neocortex consists of orderly representations or maps of receptor surfaces Figure 3 Some of the currently proposed areas of neocortex in rats. Like most other mammals, rats have a primary somatosensory area, S1, and a secondary somatosensory area, S2, a primary visual area, V1, and a secondary visual area, V2, a primary auditory area A1, and a primary motor area, M1. There is also evidence for a secondary or premotor area, M2, a dysgranular (Dys) somatosensory area...

Cortical Deafness

It has been known since at least the late 19th century that lesions to the superior temporal region in dogs, monkeys, and other species entail disorders of auditory perception. Early studies of dogs with cortical damage to this area showed, for example, that they failed to orient to sounds or respond to them normally. However, it was evident even from these early observations that such animals were not really deaf, in the sense that they did show some reaction to sounds. Furthermore, there...

Specification of Primitives and Relations

A second way in which various object perception models differ is in the elementary units, or primitives, that make up object representations. Again, Marr set the agenda by proposing a different set of primitives for each of the four stages in his object perception theory. In this framework, the image initially is represented by pixel intensity values, then the contours of the object are represented by oriented line segments, then the 2.5D structure of the object is represented by surface...

Structure from Motion

Another compelling demonstration of how motion information gives strong 3D information is the rotating cylinder example. The observer sees a 2D projection of a pattern of dots that are painted on a rotating glass cylinder rotating about a vertical (or horizontal) axis (Fig. 8). When the cylinder is static the image on the screen looks like a random array of dots. When the cylinder rotates, the dots on the front and back surfaces move in opposite directions. Moreover, the dots in the center of...

Vascular Headaches A Migraine

By definition, migraine is an idiopathic, recurring headache disorder manifesting in attacks lasting 4-72 hr (untreated or unsuccessfully treated), usually unilateral location, of pulsating quality, and of moderate to severe intensity that may inhibit or prohibit daily activities. Pain is aggravated by routine physical activity and is associated with nausea and or vomiting, photophobia, and phonophobia. History, physical, and neurological examinations do not suggest a secondary headache due to...

Temporal Lobe Lesions Impair Acoustic Processing

Lesion behavioral studies, mainly in rat, cat, and monkey, have provided limited information on the function and organization of auditory cortex. Differences in species and in experimental paradigms have led to conflicting results across studies. One major impairment associated with auditory cortical lesions in cat and monkey, however, is localization of brief sounds in space. Lesioned animals exhibit an inability to localize sound in the acoustic hemifield opposite the side of the lesion....

Influence Of The Cerebellum And The Basal Ganglia On The Motor Cortical Areas

Two main subcortical motor centers, the cerebellum and the basal ganglia, modulate the activity of cortical motor areas by providing feedback circuits. Their output nuclei the cerebellar nuclei for the cerebellum and the internal segment of the globus pallidus (GPi) and the substantia nigra for the basal ganglia receive indirect inputs from a variety of cortical somatosen-sory, motor, and associative areas and send their outputs, via the thalamus, back to the motor and premotor areas along with...

Color Discrimination Indices

Color Spectral Measurements

One way to characterize human color vision is to ask how good we are at making color discriminations. Figure 3 summarizes results from four different tests of human color vision. Just as it does for all other animals, the sensitivity of humans to light varies as a function of the wavelength of the light. The results shown in Fig. 3A illustrate this point. The continuous line is called a spectral sensitivity function and it plots Figure 3 Four measurements of human color discrimination...

Cortical Eye Fields and Saccades

Cortical Pathways for Visually Guided Saccades In primates, the cerebral cortex is a very important part of the saccadic circuitry. Although the SC seems to be the premier structure for visually guided saccades, it is not a critical component of saccade generation because the effects of SC lesions are largely transient, whereas the saccade structures downstream are vital. Thus, lesions of the saccade generator structures in the pontine and midbrain reticular formation permanently eliminate all...

Headaches of Ocular Origin

Headache is rarely due to the eye, with the exception of obvious ocular pathology. Photophobia, associated with migraine, is rarely caused by diseases of the eye, eye muscles, or the optic nerves. Reading, eye strain, eye muscle imbalance, or refractive errors are rare causes of headache. The pain of glaucoma is due to an increased intraocular pressure within the globe. The severity is more directly related to the rate of increase of the intraocular pressure rather than the absolute pressure....

Classical Aphasic Syndromes

The language disorders that are best understood are those that affect the representation and processing of language in the usual tasks of language use. These disorders are known as aphasia. By convention, the term aphasia does not refer to disturbances that affect the functions to which language processing is put. Lying (even transparent, ineffectual lying) is not considered a form of aphasia, nor is the garrulousness of old age or the incoherence of schizophrenia. Neurologists and...