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Disease processes affecting the cerebellum and its connections, such as can occur in multiple sclerosis, often lead to lack of motor coordination, postural tremor, and tremor on directed movement; these symptoms can be difficult to treat. The cerebellum generates oscillations over a range of frequencies (beta, gamma, very fast) and some of these are coherent with oscillations in thalamus and in muscle. Genetically modified ataxic mice can exhibit short runs of very fast oscillations that are gap junction dependent. Oscillations can also be induced in cerebellar cortex slices: gamma and very fast oscillations both require gap junctions, and gamma also depends on synaptic inhibition.

This chapter discusses the assessment and treatment of incorrect awkward movements and disturbed voluntary control of motor actions. Incorrect and awkward movements can occur on one or both sides of the body. Kinaesthetic ataxia affects the hand and optic ataxia affects the visual field contralateral to the lesion. Face apraxia and limb apraxia are bilateral disorders resulting from unilateral, mainly left sided, lesions. Callosal apraxia disturbs movements of the left-sided extremities. In disturbed voluntary control of motor actions, the affected limbs either do not spontaneously participate in an intended action (motor neglect) or do perform actions which are not intended (all other syndromes).

A main issue in the debate centring on the relation between perception and action is the following: how much of our actions can be performed independently from perception? An answer to this question seems to be provided in the field of motor neuroscience. Accordingly, the main paradigms in the field have tried to investigate residual visuo-motor abilities in patients with visual deficits (e.g., visually guided reach-to-grasp in cortical blindness (blindsight) or visual form agnosia, or to delineate specific visual deficits that would be specific to the action system and not affect perceptual responses (e.g., optic ataxia)). This chapter examines the conclusions which can be drawn from the investigation of optic ataxia through a review of the recent developments made in relation to this neurological condition. It argues that a general oversimplification of the dual-visual systems hypothesis (Milner and Goodale 1995) has led to the popular interpretation that ‘dorsal = action’. It challenges the claims of a neat double dissociation between the conditions observed in optic ataxia and visual agnosia, and in turn between perception and action.

Drowning is a hazard for the international traveller whether swimming, snorkeling, scuba diving, or boating. Alcohol always exacerbates the danger. Drowning in children is a particular problem. In one British study (1996–2003) 74% of drowning in children <14 years old occurred in swimming pools.

The term apraxia (Greek: inactivity) was first used to describe failures in the performance of purposeful actions and the incorrect use of objects by patients with aphasia. Apraxias are higher motor dysfunctions that affect performance and the imitation of actions or action sequences as well as the appropriate use of objects. The observed deficits do not result from paresis, ataxia, dyskinesia, paraesthesia, or the impairment of language understanding or recognition of objects. The most complex forms of apraxia are the ideational and ideomotor apraxia syndromes. They are derived from lesions of the language dominant hemisphere, though the manifestation is bilateral. In rare cases, with a lesion of the callosal fibres, a unilateral ideomotor apraxia in the extremities ipsilateral to the language dominant hemisphere can be observed.

Human cervical mechanisms are very deeply connected to the vestibular system, and the contribution of the neck reflexes in postural control is mostly hidden. Consequently, neck reflexes are a subject of minor interest in neurology; clinical practice does not provide methodology to evaluate the contribution of the neck. However, because of the increasing number of patients with cervical ataxia due to acceleration trauma, research on the topic of cervicovestibular interactions is needed in order to find a methodology to sort out the contribution of the neck and the vestibular system in postural control. As a first approach to this research field, the authors did two pilot studies on horizon perception in healthy subjects.

Recent studies suggest that, at least under neurodegenerative conditions, local brain formation of estradiol by the enzyme aromatase is an endogenous neuroprotective mechanism. This chapter reviews neuroprotective actions of aromatase and local estradiol synthesis in different experimental models of brain pathology in mammals. The cell types involved in the production of aromatase after brain injury, the role of neurogenesis and synaptic plasticity in the mechanisms of neuroprotection, the consequences of aromatase deficiency for brain function, and the possible implication of brain aromatase in the generation of sex differences in brain pathology are also discussed.

This chapter reviews recent accounts on the nature of the well-established visuo-motor deficits in optic ataxia (OA) and presents original data revealing visuo-perceptual deficits in patients with OA. The research reviewed in this chapter challenges the long-held assumption that OA occurs independently from other perceptual or attentional deficits. The findings also demonstrate that research on OA requires a fundamental reappraisal both regarding the specificity of visuo-motor deficits and regarding the careful analysis of underlying lesions and disruptions to normal connectivity caused by those lesions, which would benefit from diffusion tensor imaging techniques.

Aniridia (Greek) literally means “absence of iris” (the colored part of the eye); however, this is a misnomer because patients with aniridia always have irises that are rudimentary or not fully developed. Years ago when this eye condition was given the name “aniridia,” it was not known that the name would come to only describe the most physically noticeable aspect of the condition. Today it is known that the lack of iris is only a minor aspect of aniridia, and it does not reflect the more important aspects of aniridia that can cause even more vision loss. Aniridia has been and still is referred to as a “rare” eye condition, even though the eye conditions that make up aniridia are common ones such as glaucoma, cataract, corneal degeneration, and low vision. The “rare” aspect of aniridia is having the combination of these conditions in one individual, affecting his or her vision. Aniridia is a genetic eye condition that is congenital—that is, it is present from birth—and affects various structures of the eye. It occurs when the gene responsible for eye development, the PAX6 gene (located on the eleventh chromosome), does not function correctly. The result is developmental disorders not only of the iris, but also of the cornea, the angle of the eye, the lens, the retina (sensory part of the eye), and the optic nerve (nerve that carries visual impulse to the brain). The degree of maldevelopment differs from one patient to another. Aniridia is a bilateral disease. The incidence of this condition ranges from one in 40,000 to one in 50,000 births. It occurs equally in males and females, and has no racial predilection. Aniridia can be familial or sporadic (occurs spontaneously, not inherited). Familial Aniridia (87%): The Ocular Manifestations Occur in Isolation 85% autosomal dominant 2%autosomal recessive has been observed in the rare Gillespie’s syndrome, in which aniridia is associated with cerebellar ataxia, structural defects in the cerebellum and other parts of the brain, and mental retardation. Patients with Gillespie syndrome are not predisposed to the development of Wilms’ tumor.

Aniridia literally means “without iris.” The iris is the part of the eye that gives color to the eye. But the term aniridia encompasses more than its literal meaning and includes abnormalities of almost all the structures of the eye, from the cornea up to the optic nerve and including the angle of the anterior chamber, the lens, and the fovea. This is why aniridia is often called a “panocular disease.” The cornea is normally an avascular (lacking blood vessels), transparent tissue on the front part of the eye. In individuals with aniridia, it becomes vascularised. A bunch of blood vessels grows over the cornea: this growth is called a pannus. The angle of the anterior chamber is that part of the eye between the cornea and the iris that drains the fluid within the eye out of the eye and maintains the pressure within the eye at normal levels. Aniridia affects this part and hampers the fluid flow out of the eye, thereby increasing the pressure within the eye, leading to a condition called glaucoma. The lens is a biconvex structure behind the iris that focuses light rays entering into the eye onto the retina, which converts these light signals into electric signals that are carried through the optic nerve to the brain. In aniridia there may be displacement of the lens from its normal position, which is called subluxation or dislocation, or the normally clear lens may turn opaque, which is called a cataract. The fovea is the area of the retina that is responsible for clear vision. It may be underdeveloped; this is called foveal hypoplasia and affects vision. Similarly, the optic nerve that carries the visual sensations may also be underdeveloped, affecting vision. Besides these anatomical abnormalities, functional problems in addition to decreased vision include nystagmus (involuntary wobbling movement of the eye), squinting, and intolerance to light (photophobia). In this chapter we will discuss mainly the epidemiology (incidence and distribution of diseases) and genetic aspects of aniridia.

The previous chapter provided an overview of the anatomy of the CNS, concentrating on structures that can be seen during dissection of the human brain and spinal cord or the study of anatomical models of these structures. Some indication of the function of different components of the CNS has been given in Chapter 15, but this chapter shows how the various anatomical components of the CNS are functionally linked together through sensory and motor pathways. These pathways enable the nervous system to convey information over considerable distances, to integrate the information, and formulate functional responses that coordinate activities of different parts of the body. It will be necessary to introduce some other structures in addition to those described in Chapter 15 during the description of major pathways; most are not visible to the naked eye and even when seen in microscopical sections, they require considerable practice to distinguish them. However, they are important landmarks or relay stations in the central nervous pathways and you need to know of them for a full understanding of pathways. As emphasized in Chapter 14, our views of the structure and function of many aspects of the nervous system are constantly subject to revision in the light of new clinical and experimental observations and methods of investigation. This applies to nerve pathways just as much as any other aspect of the nervous system. This chapter presents a summary of current views on somatic sensory and motor functions and their application to the practice of dentistry. The special sensory pathways of olfaction, vision, and hearing are described in Chapter 18 in the context of the cranial nerves that form the first part of these pathways. The information conveyed from the periphery by the sensory components of spinal and cranial nerves is destined to reach the cerebral cortex or the cerebellum. You will be conscious of sensory information that reaches the cerebral cortex, but mostly unaware of information that does not travel to the cortex. However, this does not mean that sensory information that does not attain cortical levels is of no value. For example, sensory neurons or their collateral processes form the afferent limbs of many reflex arcs.

After nearly 200 years, the concept that the cerebellum modulates only motor systems has been laid to rest. In the past two decades, evidence derived from neuroanatomical, neuroimaging, neuropsychologic, and psychiatric investigations has conclusively demonstrated that the normal cerebellum plays an important role in cognition and emotion and that diseases of the cerebellum may lead to cognitive impairment and psychiatric syndromes. Cerebellar damage can be a consequence of many different diseases. The total prevalence of cerebellar disorders is unknown. Heavy alcohol use is probably the most common source of cerebellar abnormality. The cerebellum is affected in 1.5% to 8% of all strokes (Raco et al., 2003), so this is probably the second mostcommoncause of cerebellar damage. In children, the incidence of primary brain tumors is about 2.8/100,000 per year; posterior fossa tumors account for about 40% of this total (Kuttesch and Ater, 2004). In adults, primary tumors of the cerebellum are less common than in children, but metastases are more frequent. The prevalence of recessive, dominant, and sporadic neurodegenerative diseases that primarily affect the cerebellum is, in aggregate, about 6/100,000 (Durr, 2002; Margolis, 2003). Other causes of cerebellar lesions are rare. A key point is that many of these disorders do not affect the cerebellum in isolation. Therefore, once disease affecting the cerebellum is established, it is critical to determine whether other brain regions are also involved. Other relevant clinical factors include the age of the patient and the duration of degenerative illness or the length of time since a stroke or a tumor resection. A neuroanatomic underpinning for the role of the cerebellum in cognition and emotion has been established over the past 25 years (Middleton and Strick, 2000; Schmahmann, 2001). The pathway from the cerebral cortex to the cerebellum originates with axons in cortical layer Vb in motor; somatosensory; association; and paralimbic regions, including prefrontal areas critical for attention, working memory, planning, motivation, decision-making, and language. After synapse in the pons, the pathway projects to the cerebellar cortex. The pathways back from the cerebellum to the cerebral cortex begin with axons projecting from cerebellar Purkinje cells to the deep cerebellar nuclei.

An impairment becomes a disability for a child only if he/she is unable to carry out the normal activities of his/her peer group. For example, a child who has broken an arm is temporarily ‘disabled’ by not being able to eat and write in the normal way. However, impairment is a permanent feature in the lives of some children, although it may become a disability only if they are unable to take part in everyday activities, such as communicating with others, climbing stairs, and toothbrushing. A more contemporary view is one that moves away from the medicalization of impairment to a consideration of ability and functioning, enshrined in the World Health Organization’s International Classification of Functioning, Disability, and Impairment (ICF). In this definition, a number of domains are classified from body, individual, and societal perspectives. This approach is less stigmatizing and more enabling of children with impairments. There are a number of reasons why children with impairments merit special consideration for dental care. 1. The oral health of some children with disabilities is different from that of their healthy peers—for example, the greater prevalence of periodontal disease in people with Down syndrome and of tooth-wear in those with cerebral palsy. 2. The prevention of dental disease in disabled children needs to be a higher priority than for so-called normal peers because dental disease, its sequelae, or its treatment may be life-threatening—for example, the risk of infective endocarditis from oral organisms in children with significant congenital heart defects. 3. Treatment planning and the provision of dental care may need to be modified in view of the patient’s capabilities, likely future cooperation, and home care—for example, the feasibility of providing a resin-bonded bridge for a teenager with cerebral palsy, poorly controlled epilepsy, and inadequate home oral care. In the light of these considerations, do such children need special dental care? Most of the studies that have been undertaken on disabled children have indicated that the majority can in fact be treated in a dental surgery in the normal way, together with the rest of their family.

In this chapter we meet Ruth Vickers and other individuals whose visual problems seem to be the exact opposite of Dee Fletcher’s. Ruth, for example, is unable to scale her hand to the size of objects she is trying to grasp, even though she has no trouble perceiving the size of those objects. People like Ruth appear to have a deficient vision-for-action system even though the vision-for-perception system seems to be spared.