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Article

Holly Bridge

The sensation of vision arises from the detection of photons of light at the eye, but in order to produce the percept of the world, extensive regions of the brain are required to process the visual information. The majority of information entering the brain via the optic nerve from the eye projects via the lateral geniculate nucleus (LGN) of the thalamus to the primary visual cortex, the largest visual area, having been reorganized such that one side of the brain represents one side of the world. Damage to the primary visual cortex in one hemisphere therefore leads to a loss of conscious vision on the opposite side of the world, known as hemianopia. Despite this cortical blindness, many patients are still able to detect visual stimuli that are presented in the blind region if forced to guess whether a stimulus is present or absent. This is known as “blindsight.” For patients to gain any information (conscious or unconscious) about the visual world, the input from the eye must be processed by the brain. Indeed, there is considerable evidence from functional brain imaging that several visual areas continue to respond to visual stimuli presented within the blind region, even when the patient is unaware of the stimulus. Furthermore, the use of diffusion imaging allows the microstructure of white matter pathways within the visual system to be examined to see whether they are damaged or intact. By comparing patients who have hemianopia with and without blindsight it is possible to determine the pathways that are linked to blindsight function. Through understanding the brain areas and pathways that underlie blindsight in humans and non-human primates, the aim is to use modern neuroscience to guide rehabilitation programs for use after stroke.

Article

Linda Siegel

Dyslexia, or a reading disability, occurs when an individual has great difficulty at the level of word reading and decoding. Comprehension of text, writing, and spelling are also affected. The diagnosis of dyslexia involves the use of reading tests, but the continuum of reading performance means that any cutoff point is arbitrary. The IQ score does not play a role in the diagnosis of dyslexia. Dyslexia is a language-based learning disability. The cognitive difficulties of dyslexics include problems with recognizing and manipulating the basic sounds in a language, language memory, and learning the sounds of letters. Dyslexia is a neurological condition with a genetic basis. There are abnormalities in the brains of dyslexic individuals. There are also differences in the electrophysiological and structural characteristics of the brains of dyslexics. Hope for dyslexia involves early detection and intervention and evidence-based instruction.

Article

Research in the psychology of language has been dogged by some enduring controversies, many of which continue to divide researchers. Furthermore, language research has been riven by too many dichotomies and too many people taking too extreme a position, and progress is only likely to be made when researchers recognize that language is a complex system where simple dichotomies may not be relevant. The enduring controversies cover the width of psycholinguistics, including the work of Chomsky and the nature of language, to what extent language is innately determined and the origin of language and how it evolved. Chomsky’s work has also influenced our conceptions of the modularity of the structure of the mind and the nature of psychological processing. Advances in the sophistication of brain imaging techniques have led to debate about exactly what these techniques can tell us about the psychological processing of language. There has also been much debate about whether psychological processing occurs through explicit rules or statistical mapping, a debate driven by connectionist modeling, deep learning, and techniques for the analysis of “big data.” Another debate concerns the role of prediction in language and cognition and the related issues of the relationship between language comprehension and language production. To what extent is language processing embodied, and how does it relate to controversies about “embedded cognition”? Finally, there has been debate about the purpose and use of language.

Article

Hunger  

Neil E. Rowland

Hunger is a specific and compelling sensation, sometimes arising from internal signals of nutrient depletion but more often modulated by numerous environmental variables including taste or palatability and ease or cost of procurement. Hunger motivates appetitive or foraging behaviors to find food followed by appropriate proximate or consummatory behaviors to eat it. A critical concept underlying food intake is the flux of chemical energy through an organism. This starts with inputs of food with particular energy content, storage of excess energy as adipose tissue or glycogen, and finally energy expenditure as resting metabolic rate (RMR) or as metabolic rate is modified by physical activity. These concepts are relevant within the context of adequate theoretical accounts based in energy homeostasis; historically, these are mainly static models, although it is now clear that these do not address practical issues such as weight gain through life. Eating is essentially an episodic behavior, often clustered as meals, and this has led to the idea that the meal is a central theoretical concept, but demonstrations that meal patterns are greatly influenced by the environment present a challenge to this tenet. Patterns of eating acquired during infancy and early life may also play a role in establishing adult norms. Direct controls of feeding are those that emphasize food itself as generating internal signals to modify or terminate an ongoing bout of eating, and include a variety of enteroendocrine hormones and brainstem mechanisms. Additionally, many studies point to the essential rewarding or hedonic aspects of food intake, including palatability, and this may involve integrative mechanisms in the forebrain and cerebral cortex.

Article

G. Campbell Teskey

The kindling phenomenon is a form of sensitization where, with repetition, epileptiform discharges become progressively longer and behavioral seizures eventually appear and then become more severe. The classic or exogenous kindling technique involves the repeated application of a convulsant stimulus. This technique also lowers seizure thresholds, the minimum intensity of a stimulus required to evoke an electrographic seizure, a process known as epileptogenesis. Endogenous kindling typically occurs following a brain-damaging event which lowers seizure thresholds to the point where self-generated epileptiform discharges recur, lengthen, propagate, and drive progressively more severe behavioral seizures. While exogenous kindling results in alterations in neuronal molecular, cellular/synaptic, and network function that give rise to altered behavior, there is a paucity of evidence for loss of neurons. In contrast, brain-damaging events, with neuronal loss, typically give rise to endogenous kindling. Kindling is a pan-species phenomenon and all mammals that have been examined, including humans, manifest exogenous kindling when seizure-genic (forebrain) structures have been targeted. Since humans display both exogenous and endogenous kindling phenomena this serves as a sober warning to clinicians to prevent seizures. Kindling serves as a robust and reliable model for epileptogenesis, focal as well as secondarily generalized seizures, and certain epileptic disorders.

Article

Determining the mechanisms that underlie neurocognitive aging, such as compensation or dedifferentiation, and facilitating the development of effective strategies for cognitive improvement is essential due to the steadily rising aging population. One approach to study the characteristics of healthy aging comprises the assessment of functional connectivity, delineating markers of age-related neurocognitive plasticity. Functional connectivity paradigms characterize complex one-to-many (or many-to-many) structure–function relations, as higher-level cognitive processes are mediated by the interaction among a number of functionally related neural areas rather than localized to discrete brain regions. Task-related or resting-state interregional correlations of brain activity have been used as reliable indices of functional connectivity, delineating age-related alterations in a number of large-scale brain networks, which subserve attention, working memory, episodic retrieval, and task-switching. Together with behavioral and regional activation studies, connectivity studies and modeling approaches have contributed to our understanding of the mechanisms of age-related reorganization of distributed functional networks; specifically, reduced neural specificity (dedifferentiation) and associated impairment in inhibitory control and compensatory neural recruitment.

Article

Healthy aging is associated with changes in sensory, motor, cognitive, and emotional functions. Such changes depend on various factors. In particular, physical activity not only improves physical and motor but also cognitive and emotional functions. Observational (i.e., associations) and cross-sectional studies generally show a positive effect of regular physical exercise on cognition in older adults. Most longitudinal randomized controlled intervention studies also show positive effects, but the results are inconsistent due to large heterogeneity of methodological setups. Positive changes accompanying physical activity mainly impact executive functions, memory functions, and processing speed. Several factors influence the impact of physical activity on cognition, mainly the type and format of the activity. Strength training and aerobic training yield comparable but also differential benefits, and all should be used in physical activities. Also, a combination of physical activity with cognitive activity appears to enhance its effect on cognition in older age. Hence, such combined training approaches are preferable to homogeneous trainings. Studies of brain physiology changes due to physical activity show general as well as specific effects on certain brain structures and functions, particularly in the frontal cortex and the hippocampus, which are those areas most affected by advanced age. Physical activity also appears to improve cognition in patients with mild cognitive dysfunction and dementia and often ameliorates the disease symptoms. This makes physical training an important intervention for those groups of older people. Apart from cognition, physical activity leads to improvement of emotional functions. Exercise can lead to improvement of psychological well-being in older adults. Most importantly, exercise appears to reduce symptoms of depression in seniors. In future intervention studies it should be clarified who profits most from physical activity. Further, the conditions that influence the cognitive and emotional benefits older people derive from physical activity should be investigated in more detail. Finally, measures of brain activity that can be easily applied should be included as far as possible.

Article

Thirst  

Neil E. Rowland

Thirst is a specific and compelling sensation, often arising from internal signals of dehydration but modulated by many environmental variables. There are several historical landmarks in the study of thirst and drinking behavior. The basic physiology of body fluid balance is important, in particular the mechanisms that conserve fluid loss. The transduction of fluid deficits can be discussed in relation to osmotic pressure (osmoreceptors) and volume (baroreceptors). Other relevant issues include the neurobiological mechanisms by which these signals are transformed to intracellular and extracellular dehydration thirsts, respectively, including the prominent role of structures along the lamina terminalis. Other considerations are the integration of signals from natural dehydration conditions, including water deprivation, thermoregulatory fluid loss, and thirst associated with eating dry food. These mechanisms should also be considered within a broader theoretical framework of organization of motivated behavior based on incentive salience.