J) En cuanto al casco, conforme se define en el artículo 12, 4, el enfoque ha de ser distinto, sus alineaciones serán mantenidas y tan
VII. PROYECTO DE REFORMA DE LA LEY DEL SUELO
New ideas are often generated from unusual observations during routine clinical practice. It is from this origin that the dual-task paradigm developed. A clinical observation was reported by Lundin-Olsson et al [68], describing that those who had a history of falls were observed to “stops walking when talking” ([68], p617). This concept has been further developed into both an assessment and treatment approach.
12 | P a g e The dual-task paradigm involves the observation of gait during a secondary task, and has become the standard way to assess the interaction between cognition and gait [69]. The change in performance when comparing a single to a dual task is termed the “dual-task cost” (DTC). DTC can be quantified using any objective performance measure. For example, changes in gait parameters such as velocity have most frequently been used [70]. The task performance
measurements can involve speed (i.e. reaction time) or accuracy (i.e. number of correct answers) to determine the cost of completing two tasks simultaneously.
Areas of the brain or networks underlying executive function have been
identified as controlling dual-tasking [71]. Yogev-Seligman et al [71] outlined three theories which may explain the observed DTC: “capacity-sharing”, “bottle-neck”, and “multiple resource”. “Capacity-sharing” describes the performance of two attention-demanding tasks when attentional resources are limited in
capacity, causing deterioration in performance of at least one of the tasks.
“Bottle-neck” describes the situation when two tasks are processed by the same neural processor or networks at the same time. “Multiple resource” occurs when processing requires several different resources, therefore if the same resources are required, a dual-task interference will occur (and vice versa). Assessing an individual’s ability to dual-task provides insight into that individual’s executive functions and functional or clinical presentation of dysfunction [72].
Neuroplastic changes have been demonstrated within adults with mild dementia [73]. Neural plasticity is a broad term that refers to the ability of different levels of the central nervous system to change in structure and function, for both normal development and following injury [74, 75]. Plasticity of the CNS has been studied through various methods of neuroimaging techniques such as positron emission topography, functional magnetic resonance imagery, transcranial magnetic stimulation, and motor evoked potentials [74].
13 | P a g e Studies using such techniques have identified changes to brain structure and function following exercise-based interventions [76]. Lustig [76] simplifies the identification of both increases and decreases in activation: “Increases in size or activation levels are hypothesized to represent increased use of the processes mediated by a region; decreases in size or activation indicate decreased use (or increased efficiency)” ([76], p510).
It has been hypothesised that these changes in cerebral activation and location in older adults following exercise vary according to the stage of motor training or skill acquisition [77, 78]. An increase in cerebral activation indicates structural and functional changes within the brain during in the initial stage of skill
acquisition, where physical activity is novel and building capacity. A decrease in activation relates to greater efficiency in structure and function, present in the later stages of skill acquisition when a skill has been learnt and is conducted with greater speed and autonomy. DTC could follow a similar hypothesis and indicate level of skill acquisition; a higher DTC could be experienced when a new skill or task is introduced, and a lower DTC following practice and as skill attainment improves. This is a novel rationale for the introduction of DTC as an outcome measurement that has not been developed in the literature to date. However, the neuroimaging studies have been based on healthy older adults and the literature underpinning the mechanisms for neural plasticity in adults with cognitive impairment is not as well-developed [73, 76].
DTC is normal and seen in healthy young adults [79, 80]. It has been reported that there is no DTC in young healthy adults for postural sway [81] or step-time variability [82], however gait speed is reduced during completion of a second task. This change in speed could be considered the normal cost from completing a dual-task within healthy adults of any age [83]. As age increases, there is a larger additive cost on speed but not accuracy during a dual-task [83]. The
14 | P a g e effects of cognitive impairment on speed and accuracy within a dual task
assessment are less understood.
An increasing number of studies have used DTC [84]. A few associate DTC with falls risk. Beauchet et al [52] identified that slower gait speed whilst dual-tasking was “associated with recurrent falls” in frail older adults. DTC has been shown to identify people who fall in community settings when gait speed is normal [85]. Montero-Odasso et al [85] reported that people with MCI had greater DTC compared to those without cognitive impairment (gait variability CV% from single to dual-task; MCI=2.68±1.31 to 9.84±10.13,
Control=1.86±0.66 to 3.74±3.31), and that these changes were markers for falls risk. This is particularly evident in the gait variability measures [67, 85].
However, whether dual-task assessment adds value to discriminating between
“fallers” and “non-fallers” is debated. Following their meta-analysis, Menant et al [70] reported that “both single and dual task paradigms are equivalent in their predictive and discriminative validity when gait speed is used” ([70], p102). Few studies have reported gait variability measures and there were insufficient data to synthesise [70]. There is a lack of evidence regarding dual-task assessments in all gait parameters, and particularly in people with mild cognitive impairment.