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...

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...

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...

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...

Computational Capacities

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...

Conclusion

This article on brain development provides a simplified version of the subject. The process of brain development is much more complex and complicated than depicted, particularly for humans. Familial and social environment has been increasingly implicated in the development of the human brain, both structurally and functionally. Indeed, children raised in an enriched environment do better on intelligence tests than children raised under the same nutritional regime but in a poorer environment....

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...

Relevance Of The Autonomic Innervation Of The Pancreatic Islet

The brain controls islet function through the autonomic nerves. Both parasympathetic and sympathetic nerves form a dense innervation of each islet, enabling release of their neurotransmitters in close apposition to the individual islet endocrine cells. A dense parasympathetic innervation has been verified by light and electron microscopy after staining sections with cho-linesterase. Furthermore, histochemical data have shown a 10-fold higher concentration of choline acetyltransferase in islet...

The Brain Substrates Of The Classically Conditioned Nm Response In The Rabbit

Since the early 1970s, Thompson and many others have used a variety of methods to search for the classically conditioned NM response engram. A neuronal circuit diagram has been systematically constructed during the course of 20 years to represent all the brain structures that are essential for the acquisition and retention of the classically conditioned NM response for the delay conditioning paradigm. This circuit is the most thoroughly investigated and completely understood learning and memory...

Structure of the Hypothalamus

The hypothalamus in the mammalian brain encompasses the most ventral part of the diencephalon, where it forms the floor and, in parts, the walls of the third ventricle. Its upper boundary is marked by a sulcus in the ventricular wall, the ventral diencephalic or hypothalamic sulcus, which separates the hypotha lamus from the dorsally located thalamus (Fig. 2). Caudally, the hypothalamus merges without any clear limits with the periventricular gray and the tegmentum of the mesencephalon....

Synaptic Vesicles

Our thinking about neurotransmission was strongly influenced by two important discoveries made at midcentury. By using electrophysiological techniques to study nicotinic cholinergic transmission (primarily at the neuromuscular junction), Bernard Katz and his co-worker discovered that transmission is quantized. The postsynaptic responses (excitatory postsynaptic potentials, EPSPs) occur in discrete units of strength, presumably because the presynaptic component of the synapse releases ACh in...

Disorders of Sentence Production

Disturbances at the sentence production level are the inevitable results of disturbances affecting the production of simple or complex words. In addition, many patients have problems in the sentence planning process. Agrammatic patients usually produce only very simple syntactic structures. In one study, virtually no syntactically well-formed syntactic constructions were found in the utterances produced by one agrammatic patient. All the agrammatic patients studied in a large contemporary...

Multisensory Integration Evolutionary Considerations

We are far from ignorant about some of the neural mechanisms that underlie the integration of information from different sensory modalities. The study of single neurons that receive inputs from more than a single sensory modality has produced a growing body of information about the sites in the nervous system in which cross-modal convergence takes place as well as some of the mechanisms by which information from different sensory modalities is brought together and integrated. The manner in...

A Gaba Synthesis

GAD consists almost entirely of homodimers of two distinct polypeptides GAD65 (with Mr of 65,000) Figure 1 Schematic of GABA-related proteins and their locations within the cell. GAD65 or GAD67 synthesizes GABA from glutamate. GABA can be packaged into vesicles for release (vesicular GABA transporter not shown) at the synapse, where it binds to GABA receptors. GABA receptors are located on the presynaptic and postsynaptic neuron and can be found outside of the synapse. The plasma membrane GABA...

Spatial Localization of EEG and MEG

The problem of determining the spatial location of the EEG and MEG sources, their orientation, and their strength from scalp recordings is often referred to as the inverse problem. The inverse problem is ill-posed (i.e., there is no unique solution) infinitely many distributions of dipoles are consistent with any set of EEG or MEG measurements. To resolve this ambiguity, additional constraints on the solution must be placed on quantitative models, including those specified by functional...

Neural Circuitry of the Vergence Accommodation System

The primate has frontally placed eyes with highly overlapping visual fields (i.e., a large binocular field). The two retinal images are combined (fused) in the cyclopean retina (effectively located in V1). Fusion, however, requires that both eyes look in approximately the same direction so that visual objects fall on corresponding points of the two retinae. Consequently, most eye movements are conjugate because both eyes move in synchrony during nystagmus, saccades, and pursuit in order to...

Central Components

The central components of the model correspond to three potentially independent linguistic spelling routes. Two of these, the lexical-semantic route and the lexical-nonsemantic route, are used for spelling familiar words. In contrast, plausible spellings for unfamiliar words or pronounceable nonwords (e.g., sprunt) are assembled by the nonlexical route. An additional central component that receives and temporarily stores the abstract orthographic representations computed by the three spelling...

Memory as Change of Synaptic Structure and Efficacy

A complete discussion of neuronal function and synaptic transmission of information is beyond the scope of this article. Briefly, a synapse is a functional juxtaposition of two or more neurons (Fig. 4). When a neuron is stimulated to a sufficient degree, chemicals known as neurotransmitters are released from its axon terminal into the microscopic space that separates it from its neighboring neuron. The presence of neuro transmitters within this region produces characteristic changes in the...

Biological Theories Of Depression

Depression can be caused by specific biological conditions, including strokes, nutritional deficiencies, and infections. In these cases, the diagnosis mood disorder due to a general medical condition is given. Depression can also be the result of alcohol or substance abuse, often associated with the symptoms of withdrawal and intoxication. In these cases, the diagnosis substance-induced mood disorder is appropriate. Apart from these two categories, however, the role of biological causes in the...

Corpus Callosum And Consciousness

The study of split-brain patients during the past 40 years has helped change our understanding of the nature of consciousness. It has offered a prime example of the modularization of cognitive processes and documented the distinctions between a dominant and nondominant hemisphere. It has raised the question of whether the callosum may have played a unique role in the development of human consciousness. One of the key observations made regarding the Vogel and Bogen series of commissurotomies was...

Hypothalamic Organization

As its name implies, the hypothalamus is found below the thalamus in the diencephalon (Fig. 1). It is Encyclopedia of the Human Brain Volume 2 Copyright 2002, Elsevier Science (USA). Figure 1 The disposition of the hypothalamus in relation to other regions of the central nervous system is illustrated in sagittal and ventral exposures of the human brain. In sagittal exposures of the brain the hypothalamus occupies a small region bounded by the anterior commissure (AC), optic chiasm (OC), and...

Treatments Available For Anomia

Naming abilities in aphasics recover over time. Indeed, it appears that there may be slow progressive recovery in the ability to name objects and actions over time even years after the aphasia-producing incident and long after treatment has ended. However, some aphasics who have, according to all aphasia tests, fully recovered from their aphasia, nevertheless report feeling that they cannot always find the words they need in conversation. Despite the apparent spontaneous recovery of naming...

Regional Differences in Cytoarchitecture

Based on microscopic differences in the organization of the six layers, multiple distinct regions of the cerebral cortex can be defined. One of the best known maps of the cytoarchitecture of the cerebral cortex is that of Brodmann, which lists 52 different areas. Although there are subtle differences that are used to distinguish these many areas, the most simplified point of view is to consider only two major types of neocortex. The first is agranular cortex in which there is a relative lack of...

Blood Supply

The brain is extremely vulnerable to even a momentary reduction in or loss of blood flow, and an uninterrupted supply of well-oxygenated blood is critical. A complex system of arteries and veins convey blood to and from the brain, and interruption of the vascular system may result in stroke, one of the most common and devastating neurologic disorders. The arterial supply of the brain comes entirely from four major vessels that originate in the neck (Fig. 4). The right and left common carotid...

The Mesencephalic Reticular Formation

Work in the 1930s and 1940s established the importance of the brain stem reticular formation and its ascending projections in the sleep-wake cycle and arousal. In experiments in the cat, Frederic Bremer had shown that knife cuts at different levels of the neuraxis had different effects on the patterns of sleep and wakefulness. A knife cut made between the inferior and superior colliculi (which Bremer called the ''cerveau isole'' preparation) resulted in a persistent sleeplike state from which...

Using Neurofeedback to Change Attentional States

Following the early work on seizures, Joel Lubar and others began to work on a neurofeedback application to help improve the attentional abilities of children and adults with attention deficit disorder (ADD or ADHD). A great deal of research has indicated that ADD is often accompanied by an excess of slow brain waves, especially during less compelling tasks such as might be found in school. The predominance of 6 (4-7 Hz) activity versus b (13-22 Hz) activity at the central vertex of the cranium...

Mercury

Symptoms of acute exposure to elemental mercury vapor include respiratory irritation, headache, fever, chills, chest pain, general malaise, nausea, and vomiting. These symptoms are often referred to as metal fume fever syndrome.'' Emotional lability, depression, social withdrawal, tremors, delirium, and coma develop within 24 hr after exposure to elemental mercury. The respiratory symptoms typically resolve within days to weeks after cessation of exposure, but the CNS disturbances persist. The...

Epithelial Design of Nervous Tissue

As stated, nervous tissue is a specialized epithelial tissue. Epithelia are sheets of cells that cover surfaces or line cavities of the body and in places grow into subjacent connective tissue to form hair follicles, glands, or other derivatives. Features of epithelia include close aggregation of functionally related cells, small amounts of intercellular substance, a basement membrane, a free surface, and utter avascularity. Nervous tissue, wherever encountered clearly shows the first two...

B Gaba Degradation The GABA Shunt

GABA-transaminase (GABA-T) is the main degrada-tive enzyme for GABA, although steady state GABA levels are normally controlled by GAD. GABA is degraded to succinic semialdehyde (SSA) by GABA-T, a mitochondrial enzyme. Since SSA can be converted to succinate by succinic semialdehyde dehydrogenase (SSADH), GABA can serve as one step in a shunt that bypasses a-ketoglutarate dehydrogenase in the tricarboxylic acid (TCA) cycle. The GABA shunt begins with the conversion of a-ketoglutarate to...

Affect Mood and Psychological Functioning

Standardized measures of mood, personality, and psychopathology can be used to assess the contribution The examinee is asked to recite familiar sequences such as the alphabet, days of the week, months of the year, and numbers from 1 to 20 as quickly as possible. The examinee then must recite all sequences, except the alphabet, in reverse order. Serial subtractions involve subtracting a particular number until a predetermined point is reached. The patient hears a series of alternating numbers...

Clinical Presentation

Limited information on the clinical characteristics of individuals in the persistent vegetative state is available, but it is estimated that approximately 25,000 adults in the United States carry the diagnosis. In one group of nursing home patients, persistent vegetative state was diagnosed in 3 of the individuals. The age of afflicted individuals ranged from 19 to 96 years and the duration of the persistent vegetative state ranged from 1 to 16.8 years. Twenty-five percent of the patients were...

Cortical Connections of Area V2

The organization of corticocortical connections between areas V1 and V2 in human visual cortex has been studied using the neuronal tracer DiI perchlorate) in aldehyde-fixed post mortem brain tissue. DiI injections Figure 6 Surface rendering of the two hemispheres from 10 brains illustrating the variability in the locations of areas 17 and 18. From Amunts et al. (2000). Figure 6 Surface rendering of the two hemispheres from 10 brains illustrating the variability in the locations of areas 17 and...

Handedness And Longevity

The data suggest that a significant number of lefthanders arrived at their left-handedness through some form of pathological event during their fetal development or associated with their birth, and that this same pathology also resulted in other physical or psychological problems. From Table I, it should be clear that a number of these problems, especially those associated with reduced immune system efficiency, might represent major health risk factors. Since the late 1970s a number of studies...

Epimere versus Hypomere and the Development of Striated Muscles in the Head

To appreciate the resolution of the problem of head musculature and its innervation, one must consider it in the context of the pattern of development of the muscular components of the body. The body is essentially a tube with three layers an outer layer of ectoderm that forms the central nervous system, the neural crest, the epidermis, and other tissues an inner layer of endoderm that forms the lining of the gut and related organs and an intermediate layer ofmesoderm that forms the bones,...

Cingulate Cortex What And Where

Cingulate cortex is located in the medial walls of the cerebral hemispheres and is a subset of limbic Encyclopedia of the Human Brain Volume 1 Copyright 2002, Elsevier Science (USA). cortex. Limbic cortex includes all areas that receive fibers of anterior thalamic neurons. By modern convention, the subset of limbic cortex constituting cingulate cortex includes Brodman's areas 24 and 29 in small animals such as rabbits and rats. These and an additional area (23) constitute cingulate cortex in...

Perceptual Organizational

Musical perception can also be studied at the level of the perceptual organization of auditory events along these basic perceptual-acoustic axes, both when the events occur simultaneously or overlap in time, and when they are extended across time sequentially. Although the previous section touched on this level, the following discussion focuses on the perceptual organization of multiple auditory events. As discussed in the previous section, there is considerable evidence supporting a critical...

Ethnic and Racial Issues

African Americans are the largest minority group in the United States, although by the Year 2009, Hispanic Americans are expected to outnumber African Americans. African Americans are far more likely to die of stroke than are whites or Hispanic Americans, and this is true for both ischemic and hemorrhagic cerebral infarction. Hispanic Americans are no more likely than non-Hispanic whites to die of ischemic infarction, but they are more likely to die of intracerebral hemorrhage. The reasons for...

Definition Of Mental Retardation

The definition of mental retardation has been modified several times throughout the years. For the sake of brevity, the numerous reconceptualizations and recapitulations of the definition of mental retardation are not discussed in full. Despite variability in definition, the definitions have held constant with the inclusion of impairments in cognitive and adaptive abilities. One of the major changes in definition occurred in the 1950s when a limitation in adaptive behavior was included as a...