Movement has long struck me as a funny thing. The general population regard it as a simple, automatic process and cast not another thought towards it; yet it is an incredibly complex synchronization of neuronal activity and muscular response. I will not ramble into the intricacies of this, but like many facets of the brain’s role in our daily life, we are still only scratching the surface of our understanding of such mechanisms. What I will bring to your attention is an exercise many of us engage in every day: walking.
It can easily be taken for granted that our locomotive abilities deplete with age: an elderly man’s stiff, heavy-footed shuffle shows only the thinnest ghost of a young boy’s playful, prancing step. This could be attributed to our muscular and general body function. We get old and we begin to feel all the aches and pains of living a long life. But we could imply that there is more to the change in our pace that the simple wear-and-tear the years have brought us. A variety of regions in the cerebral cortex influence our gait and the natural atrophy of our brain could change the manner and capacity of their function.
However, aging is not the only factor that changes our swagger. Neurological disorders, causing lesions to cerebral regions involved in gait, can become obvious through our walk. The most prominent example of this is the parkinsonism gait: small, shuffling steps and an overall slow pace. Indeed, in his book “Phantoms in the brain”, V.S. Ramachandran (2005) described an old professor of his instructing his medical class to diagnose Parkinson’s Disease with their eyes closed – simply by listening to the dragging sound of their feet as they walked. When we consider the cognitive components captured by locomotion, such an abnormality is not unfounded. Gait is directed by goals, thus is mediated by attentional circuits (Rochester, Galna, Lord & Burn, 2014). This involves frontal lobe activity, which is disrupted in Parkinson’s Disease due to the dysfunction of the basal ganglia. In the case of parkinsonism, velocity and stride length is predominately affected, but multiple sites within the cortico-basal ganglion-thalamic circuit can cause varying degrees of gait disturbances (Elble, 2007). As in Parkinson’s Disease, movement ability has been shown to decline years prior to the onset of cognitive impairments in the other common dementia subgroups (Montero-Odasso, Verghase, Beauchet & Hausdorff, 2012).
The Dynamic Relationship Between Gait and Cognition
That finding has opened a new area of research: the complementary relationship between gait and cognition. To discuss this, let us first examine the regions of the brain implicated in successful gait. We’ve already mentioned the frontal lobes’ role in attention, a fundamental component of locomotion. This area is also associated with executive function, which (depending on the paper) can describe a wide range of every day tasks: problem-solving, set-switching, working memory, reasoning, etc. These abilities are vital for engaging in our environments, allowing us to move through the world safely and efficiently. Without them, we are at risk of several locomotive problems, such as postural instability and falling (Montero-Odasso & Hachinski, 2014). This will be explained later in regards to the increasing demand accurate gait places on the cognitive resources of the diseased brain. The frontal subcortical networks controlling motor and cognitive abilities are located closely to one another, lending an explanation as to why white matter disease or frontal atrophy may simultaneously affect both gait and executive function. The temporal lobe also plays an important part in gait ability, due to its role in spatial navigation and memory (Annweiler, Beauchet, Bartha & Montero-Odasso, 2013). Unsteady and uncoordinated gait may result from lesions to the hippocampal area, as they would allow a deficit in the recall of the complex sequences of movement necessary for walking. Imaging studies have correlated medial temporal lobe atrophy with mild cognitive impairment (MCI; Annweiler et al., 2013). Lastly, it has been suggested that the parietal cortex’s integration of visuospatial, cognitive and motor information could have an impact on an individual’s gait.
Research into MCI’s relationship with gait has begun to spring up in the last number of years. MCI is described as a predementia state, with individuals developing either amnesic or other cognitive impairments (Montero-Odasso, Oteng-Amoako, Speechley, Gopaul, Beauchet, Annweiler & Muir-Hunter, 2014). The current proposal behind the correlation in gait disturbances and cognitive failing is as follows: with age or disease, the automatic processes that the subcortical areas engage in to ensure smooth gait weaken, leading to a need for an increase in voluntary cortical mechanisms (Gillain, Warzee, Lekeu, Wojtasik, Maquet, Croisier… & Petermans, 2009). In essence, we begin to find it necessary to think about how we walk. Using this principle, our clever researchers have begun to develop a method in which to utilize gait analysis as a diagnostic tool for MCI. Lundin-Olsson’s (1997) seminal study “Stop walking when talking” introduced a new technique to predict falls: the dual task. This hypothesizes that walking while performing a secondary, cognitively engaging task will create competition between the brain’s resources, causing an interference effect. The modifications we must automatically make to our gait in order to navigate around our environments are described as “costs” in relation to the diseased brain (Montero-Odasso & Hachinski, 2014). Hence, an individual who has yet to reveal cognitive deficits may reveal subtle gait impairments when asked to engage in a dual-task. These disturbances occur due to the cognitive stress placed on the neural networks mediating these tasks, and as such may be facilitated for the early prediction of MCI.
Gait Analysis and Dementia
These researchers are now beginning to apply these findings to the early prediction of dementia. This is a crucial area to develop, as dementia is becoming increasingly prevalent with our growing elderly population; approximately 8% of our over 65s are diagnosed with it, with as high as 35% of the over 85 age group reported to have it (Montero-Odasso et al., 2012). This not only takes a toll on the individuals suffering from dementia and their loved ones, it also places a rising monetary cost on society (Hurd, Martorell, Delavande, Mullen & Langa, 2013). Early diagnosis and treatment of dementia is currently the most feasible way forward to bring down both of these burdens. Gait analysis is a “cheap and cheerful” method in which to diagnose such diseases, as other techniques (such as neuroimaging) may not be suitable to individuals with limited resources (Verghese, Annweiler, Ayers, Barzilai, Beauchet, Bennett, … & Wang,2014). It is also quite applicable for early diagnosis, as gait disturbance has been observed up to 12 years prior to cognitive onset of dementia; this is certainly suitable for the most common sub-type, Alzheimer’s Disease, in which the neurodegeneration can begin as early as 20 years before obvious symptoms appear (Montero-Odasso et al., 2012). As it stands, the diagnostic measures are not overtly different from those from MCI; the employment of dual-task should sufficiently indicate an underlying cognitive disorder. What the literature is lacking is an accurate utilization of gait analysis in differentiating early signs of the dementia sub-groups. Some studies have shed light onto this matter by describing different failing gait characteristics for different dementias; a fine example is the growing body of evidence for motoric cognitive risk syndrome as a predictor of vascular dementia (Verghese et al., 2014). Another study has suggested that a deficit in gait rhythm could indicate underlying Alzheimer’s Disease pathology (Verghese, Wang, Lipton, Holtzer,& Xue, X. 2007). Although this shows a start on the path forwards, we still have a long way to go before we find the answers we’re looking for.
The first steps into this treasure-trove of research are being made, and I, for one, am excited to see the kinds of hidden gems waiting to be discovered.
Annweiler, C., Beauchet, O., Bartha, R., & Montero-Odasso, M. (2013). Slow gait in MCI is associated with ventricular enlargement: results from the Gait and Brain Study. Journal of Neural Transmission, 120(7), 1083-1092.
Blakeslee, S. & Ramachandran, V.S. (2005). Phantoms in the Brain: Human nature and the architecture of the mind. London: Harper Perennial
Elble, R. J. (2007). Gait and dementia: moving beyond the notion of gait apraxia. Journal of neural transmission, 114(10), 1253-1258.
Gillain, S., Warzee, E., Lekeu, F., Wojtasik, V., Maquet, D., Croisier, J. L., … & Petermans, J. (2009). The value of instrumental gait analysis in elderly healthy, MCI or Alzheimer’s disease subjects and a comparison with other clinical tests used in single and dual-task conditions. Annals of physical and rehabilitation medicine, 52(6), 453-474.
Hurd, M. D., Martorell, P., Delavande, A., Mullen, K. J., & Langa, K. M. (2013). Monetary costs of dementia in the United States. New England Journal of Medicine, 368(14), 1326-1334.
Lundin-Olsson, L., Nyberg, L., & Gustafson, Y. (1997). “Stops walking when talking” as a predictor of falls in elderly people. The Lancet, 349(9052), 617.
Montero-Odasso, M., & Hachinski, V. (2014). Preludes to brain failure: executive dysfunction and gait disturbances. Neurological Sciences, 35(4), 601-604.
Montero-Odasso, M., Oteng-Amoako, A., Speechley, M., Gopaul, K., Beauchet, O., Annweiler, C., & Muir-Hunter, S. W. (2014). The motor signature of mild cognitive impairment: results from the Gait and Brain Study. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, glu155.
Montero‐Odasso, M., Verghese, J., Beauchet, O., & Hausdorff, J. M. (2012). Gait and cognition: a complementary approach to understanding brain function and the risk of falling. Journal of the American Geriatrics Society, 60(11), 2127-2136.
Rochester, L., Galna, B., Lord, S., & Burn, D. (2014). The nature of dual-task interference during gait in incident Parkinson’s disease. Neuroscience, 265, 83-94.
Verghese, J., Annweiler, C., Ayers, E., Barzilai, N., Beauchet, O., Bennett, D. A., … & Wang, C. (2014). Motoric cognitive risk syndrome Multicountry prevalence and dementia risk. Neurology, 83(8), 718-726.
Verghese, J., Wang, C., Lipton, R. B., Holtzer, R., & Xue, X. (2007). Quantitative gait dysfunction and risk of cognitive decline and dementia.Journal of Neurology, Neurosurgery & Psychiatry, 78(9), 929-935.