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Indirect Memory Tests Motor Learning Older adults are clearly impaired on most features of motor performance medicine 4h2 pill buy 500 mg depakote fast delivery, including speed of movement medications on airline flights trusted 250mg depakote, perceptual functioning, target tracking, use of spatially incompatible stimulusresponse mapping, and so forth (Welford, 1985). What is less clear, however, is the effect of old age on the ability to learn and retain new motor skills. One common task used to study motor learning involves a pursuit rotor, or a computerized analogue thereof. In that task, the subject is instructed to keep the tip of a hand-held stylus in continuous contact with a moving target. Motor skill is measured by the proportion of time that the subject can in fact keep the stylus in contact with the target during a time-limited trial; motor learning is evidenced by increased time-on-target across repeated trials. Older adults demonstrate learning at a slower rate than younger adults (Ruch, 1934; Wright & Payne, 1985). Similar tasks, where subjects are only able to view their hand and the tracking target in a mirror (Ruch, 1934; Wright & Payne, 1985) also show age-related impairments in learning. A potential confound plaguing these studies concerns the fact that the experimenter controls the pace in each of the tasks. Given that older adults tend to be slower at performing motor tasks, experimenter paced tasks may put older adults at a disadvantage relative to younger adults, thereby making it difficult to determine whether age-related impairments in learning are due to memory difficulties or more peripheral motor difficulties. In contrast, age differences have not been found on tasks where the task is subject paced, and requires learning of a sequence of motor movements or a new stimulus-response mapping. Wishart & Lee (1997) required subjects to produce a continuous movement comprising three distinct spatial segments, each with specific timing requirements. Learning was assessed by rate of initial acquisition and subsequent reacquisition, as well as transfer to a similar task. Although older adults performed less accurately and consistently on the task, there were no age-related differences on any of the three measures of learning. Similar results have been found with the serial four-choice response time task in which the stimuli appear in a repeating sequence. Subjects pace the task themselves: the next stimulus in the sequence is not presented until the subject responds. Even though subjects are often unaware of the repeating sequence, learning is evidenced by decreased reaction times after several repetitions. Older adults show normal learning in this task (Howard & Howard, 1989), even when the stimulus and response are spatially incompatible, thus requiring new stimulus-response mapping (Willingham & Winter, 1995). Again, no age-related differences in learning have been found, even when the older adults had never used a computer mouse before (Willingham & Winter, 1995). A possible exception to this conclusion is a finding by Harrington & Haaland (1992). The researchers used a serial response time task, but instead of pressing a key, subjects had to respond to each stimulus with a different hand posture. Willingham (1998) argued that age differences on this task could be explained in terms of speed of processing limitations. Even though the task is subject paced, subjects are required to maintain multiple cognitive processes simultaneously in order to both learn the repeating sequence and map the stimuli onto the appropriate hand posture. According to the "simultaneity mechanism" (Salthouse, 1996), products of an early mental operation that are needed for a later operation may be lost due to slowness in executing the later operation. Through this mechanism limitations on processing speed may hamper the ability to coordinate multiple streams of processing. Visuospatial Memory Closely related to motor learning is memory for visuospatial information. Age-related decline in memory for spatial location has been widely reported in the literature. Several recent studies have incorporated ecologically valid procedures that require subjects to move about during encoding, allowing the integration of sensorimotor information.

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Hence 4 medications at target buy depakote with amex, within the accuracy that the boundaries of the left ventricular wall can be treated as ellipsoids of revolution 97140 treatment code order depakote 500mg online, the assumption that the ellipsoids are confocal appears to be a good one. Within individual species, the ratio of heart weight to body weight is somewhat lower in mature rabbits and rats (about 2 g/kg) than in humans (5 g/kg) and higher in horses and dogs (8 g/kg) [6]. The rate of heart growth with body weight decreases Cardiac Biomechanics 54-5 with age in most species but not in humans. At birth, left and right ventricular weights are similar, but the left ventricle is substantially more massive than the right by adulthood. Although the myocytes are relatively short, they are connected such that at any point in the normal heart wall there is a clear predominant fiber axis that is approximately tangent with the wall (within 3 to 5 in most regions, except near the apex and papillary muscle insertions). Each ventricular myocyte is connected via gap junctions at intercalated disks to an average of 11. The classical anatomists dissected discrete bundles of fibrous swirls, though later investigations showed that the ventricular myocardium could be unwrapped by blunt dissection into a single continuous muscle "ban" [9]. However, more modern histological techniques have shown that in the plane of the wall, the mean muscle fiber angle makes a smooth transmural transition from epicardium to endocardium (Figure 54. About the mean, myofiber angle dispersion is typically 10 to 15 [10] except in certain pathologies. Similar patterns have been described for humans, dogs, baboons, macaques, pigs, guinea pigs, and rats. In the left ventricle of humans or dogs, the muscle fiber angle typically varies continuously from about -60. There are also small increases in fiber orientation from end-diastole to systole (7 to 19), with greatest changes at the epicardium and apex [11]. Regional variations in ventricular myofiber orientations are generally smooth except at the junction between the right ventricular free wall and septum. A detailed study in the dog that mapped fiber angles throughout the entire right and left ventricles described the same general transmural pattern in all regions including the septum and right ventricular free wall, but with definite regional variations [3]. Transmural differences in fiber angle were about 120 to 140 in the left ventricular free wall, larger in the septum (160 to 180) and smaller in the right ventricular free wall (100 to 120). A similar study of fiber angle distributions in the rabbit left and right ventricles has recently been reported [12]. For the most part, fiber angles in the rabbit heart were very similar to those in the dog, except for on the anterior wall, where average fiber orientations were 20 to 30 counterclockwise of those in the dog. The locus of fiber orientations at a given depth in the ventricular wall has a spiral geometry that may be modeled as a general helix by simple differential geometry. The position vector x of a point on a helix inscribed on an ellipsoidal surface that is symmetric about the x1 axis and has major and minor radii, a and b, is given by the parametric equation, x = a sin t e1 + b cos t sin wt e2 + b cos t cos wt e3 (54. The fiber angle or helix pitch angle, varies along the arc length: sin = a 2 cos2 t + b 2 sin2 t + b 2 w 2) cos2 t + b 2 sin2 t (a 2 (54. LeGrice and colleagues [19] investigated Cardiac Biomechanics 54-7 these structures in a detailed morphometric study of four dog hearts. They describe an ordered laminar arrangement of myocytes with extensive cleavage planes running approximately radially from endocardium toward epicardium in transmural section. Like the fibers, the sheets also have a branching pattern with the number of branches varying considerably through the wall thickness. The fibrous architecture of the myocardium has motivated models of myocardial material symmetry as transversely isotropic. The transverse laminae are the first structural evidence for material orthotropy and have motivated the development of models describing the variation of fiber, sheet, and sheet-normal axes throughout the ventricular wall [21].

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Development of Visuospatial Short-term Memory Like the phonological loop symptoms kidney failure generic depakote 500 mg on-line, the visuospatial sketchpad markedly increases in capacity during the childhood years treatment 20 initiative buy generic depakote 250 mg line. In order to assess this subsystem of working memory adequately, it is necessary to employ stimuli that cannot be verbally recoded in order to gain access to the phonological loop, a common strategy in children beyond about 7 years of age (Hitch et al. Further information on suitable methods for assessing visuospatial shortterm memory are provided by Della Sala et al. The precise mechanisms underpinning the developmental improvements in visuospatial short-term memory are as yet not fully understood. One debate concerns whether or not there are separable visual and spatial memory systems that undergo independent development (Logie & Pearson, 1997; Pickering et al. Other research has indicated that at least part of the sizeable improvements in visuospatial short-term memory function with age reflects increasing dependence on either the central executive (Wilson et al. Detailed discussion of these and other possible nonvisual recoding strategies contributing to the development of visuospatial short-term memory is provided by Pickering (2001). The Central Executive In adults, central executive activity has been found to be strongly associated with bilateral activity in the dorsolateral prefrontal cortex. Interestingly, the frontal lobe undergoes more extended development than other areas. Diamond, 1990), with metabolic activity not reaching adult levels until adolescence (Elman et al. Development of the Central Executive the capacity of the central executive, like that of the other two components of working memory, undergoes an extended period of development during the childhood years. Central executive function is typically assessed using tasks, also termed "complex working memory tasks", which have significant processing and storage loads. An example of such a task is listening span, in which an individual has to verify some feature of each of a series of spoken sentences at the same time as retaining the sequence of the final words of the preceding sentences (Daneman & Carpenter, 1980). Another memory task considered to have a significant central executive component is backward digit recall, which involves recalling a digit sequence in the reverse order to its original presentation. Each of these tasks clearly requires processing and/or transformation of material as well as storage. Data from Pickering & Gathercole (2001) the two major classes of explanation that have been advanced for these developmental changes have emerged largely from a school of North American research focusing on general working memory. For the present purposes, the terms "central executive" and "working memory" can be used more or less synonymously, although they have emerged from two quite distinct empirical and theoretical traditions. The major distinction between the two frameworks is the extent to which the major constraint on working memory is viewed as either the processing demands of specific activities or a general capacity for controlling attention. Daneman & Carpenter, 1980; Just & Carpenter, 1992), working memory is fuelled by a limited capacity processing resource which can be flexibly allocated to meet the processing and storage demands of complex cognitive activities. Thus, in tasks in which processing and storage demands exceed the available capacity, there will be a tradeoff between processing and storage activities: the greater the resource devoted to ongoing processing, the less that there will be available to dedicate to storing the products of processing activities. Thus, as the child grows older and more skilled at processing and manipulating information, the amount of resource required to support processing decreases and memory storage capacity increases. They demonstrated that performance on complex working memory tasks is strongly influenced by the time over which children must store items in short-term memory, with greater memory delays being associated with increased storage decrements. This feature of memory performance cannot readily be accommodated by a processing/storage tradeoff account. Instead, it points to the possibility of age-related changes in task-switching behaviour and in decay functions as possible origins of the striking differences found in complex working memory performance at different points in childhood. An alternative conceptualization of complex working memory emphasizes selective attention rather than processing efficiency per se as the major constraint on task performance. Findings of close associations between estimates of working memory capacity for different domains of activity. Jurden, 1995)are consistent with this view that working memory performance is constrained by a single general factor, rather than by processing expertise in particular domains. Although this framework has primarily been developed and applied to the understanding of individual differences in complex working memory, rather than development, there is evidence for age-related changes in attention underpinning the improved working memory capacities in older children. The results showed that age-related changes in performance were not specific to either verbal or visuospatial domains, and were related to the memory access and storage demands of the activities, rather than to processing demands. Swanson argues on this basis that the amount of activation of long-term structures changes with age, due to increase availability of attentional resources as children grow older.

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