Language and Communication Deficits in Alzheimer’s Disease: A Review of the Literature on the Progression, Prevention, and Mediation of Language Barriers Experienced by Individuals with Alzheimer’s Disease

Alzheimer’s disease (AD) poses a significant societal problem with regard to the quality of life in the aging population worldwide (Alzheimer’s Association, 2021). One ability that is affected early on in the disease is language processing, which can result in feelings of isolation due to its significant impact on one’s relationships, overall communicative ability, and quality of life (Szatloczki et al., 2015). Thus, it is of great importance to identify evidence-based interventions and preventative measures, as well as communication strategies, helpful to patients and their caregivers. In this review of literature, we examined language difficulties pertaining to semantic verbal fluency, word finding, and discourse markers, while also identifying the neural mechanisms likely responsible (e.g., Arnoff et al., 2006; Chapman et al., 1998; Eriksson et al., 2015; Pakhomov et al., 2018). In addition, we present research on the theory of cognitive reserve as a preventative measure, with a special emphasis on the influence of bilingualism (Bialystok et al., 2007; Gold, 2016; Perani et al., 2017) and music training (Chaddock-Heyman et al., 2021; Lyu et al., 2018). The research supports the efficacy of various interactive music therapies to allow extended communication between caregivers and AD patients, especially since later life music therapy can help preserve or enhance memory and language ability in patients with moderate or severe AD (Clare et al., 2020; Lyu et al., 2018; Wong et al., 2019). Future research could further investigate the long-term effects and applications of language and music interventions. Importantly, incorporating increasingly diverse samples is necessary to increase generalizability of the research described (Brewster et al., 2018; Ferretti et al., 2018). LANGUAGE AND COMMUNICATION DEFICITS IN ALZHEIMER’S 3 Language and Communication Deficits in Alzheimer’s Disease: A Review of the Literature on the Progression, Prevention, and Mediation of Language Barriers Experienced by Individuals with Alzheimer’s Disease According to the United Nations Department of Economic and Social Affairs (2017) , the world’s population of older adults has not only been on the rise but is projected to continue to increase throughout the next couple of decades. In 2017, they reported that the population of individuals over the age of 60 was recorded as 962 million, nearly doubling the amount recorded in 1980. It is projected that by the year 2050, this population will double again, rising to nearly 2.1 billion. As the older adult population increases, it is imperative that academic research unique to this population increases as well, particularly research that contributes to the well-being and quality of life of older adults. Alzheimer’s Disease (AD), which is characterized by the progression of memory decline and other cognitive impairment, poses a unique risk to the older adult population, warranting a need for in-depth attention to the details of risk, prevention, care and cause of this disease (Alzheimer’s Association, 2021). Additionally, it should be understood that dementia is an umbrella term that describes the symptoms of neurodegenerative diseases that are distinct from normal aging, the most common of which is AD. Currently, AD and other dementias have no cure. The Alzheimer’s Association (2021) provides important insight into the severity of AD in their yearly Facts and Figures report. In their most recent 2021 report, they indicate that, worldwide one in three seniors die as a result of AD or another dementia, with more people dying from dementia than breast cancer and prostate cancer combined. As a result of the COVID-19 pandemic, they report that the deaths of Americans by AD increased by 16%. The Alzheimer’s Association (2021) points toward a strong potential concern regarding the LANGUAGE AND COMMUNICATION DEFICITS IN ALZHEIMER’S 4 implications of race and ethnicity of AD in the United States. While Black Americans and Hispanic Americans are more likely to develop AD, they are less likely to be diagnosed with it. Additionally, only 53% of Black Americans believe that a future cure for AD would be shared equally regardless of race, color, or ethnicity. For the United States, treatment and care for seniors with AD and other dementias cost the nation over $355 billion in 2021, and by 2050, it could cost the nation as much as $1.1 trillion. Because interventions for these diseases are not likely to come from pharmaceuticals alone, the Alzheimer's Association stresses that successful intervention involves helping people maintain mental functioning, managing behavioral symptoms, and delaying the progression of symptoms of the disease. Therefore, it is of the utmost importance to identify the early signs of AD and engage in early interventions because adults who have received early risk identification are much more likely to be successful in mitigating the symptoms of these neurodegenerative diseases. Some of these precursor signs to detect AD include memory loss that affects daily activities, challenges in planning or completing familiar tasks, withdrawal from work or social activities, and, for the interest of this paper, problems with speaking or writing—across all languages that one speaks. Fortunately, recent research has discovered many known protective factors that can reduce the likelihood of getting dementia or other neurodegenerative diseases, as well as improve the management of behavioral symptoms from dementia, such as bilingualism, music therapy, and cognitive reserve in general (Stern, 2012; Tsoi et al., 2018). While we believe the focus of research on AD and other dementias should always be towards finding a cure, much of the research should also continue to identify the activities and lifestyles the average person can participate in to possibly protect themselves from or delay the onset of AD and other neurodegenerative diseases. LANGUAGE AND COMMUNICATION DEFICITS IN ALZHEIMER’S 5 The focus of this current project is consistent with this latter goal by emphasizing the neural underpinnings and language deficits that are concurrent with the onset of AD, as well as the qualities of various lifestyle factors that may contribute to cognitive reserve as a protective factor in older age. To do this, we review some of the research about the nature of language difficulties faced by older adults who are experiencing early symptoms of AD before and soon after a diagnosis. While in this transitional stage, individuals may also start to exhibit brain abnormalities consistent with pathological AD, such as the presence of beta-amyloid plaques and neurofibrillary tangles (Reilly, 2011). Second, some research regarding the implications of preventative factors on the expression and progression of AD and other dementias is discussed, particularly in relation to cognitive reserve with a particular emphasis on music training and bilingualism (Bialystok et al., 2007; Chaddock-Heyman et al., 2021; Gold, 2016; Harvard Health Publishing, 2017; Peck et al., 2016; Perani et al., 2017; Stern, 2012; Tsoi et al., 2018). We conclude by discussing how our research may be utilized in facilitating communication between caregivers and patients with AD, as well as the general limitations and possible future directions for research. Neuropathology of Alzheimer’s Disease Reilly (2011) describes several key components in the neuropathology of Alzheimer’s Disease (AD). Patients with AD suffer from significant brain atrophy “in frontal, parietal and temporal gyri, particularly entorhinal cortex and hippocampus, with commensurate ventricular enlargement” causing a decrease in brain weight and volume (Reilly, 2011, p. 18). Such damage commonly results in executive, behavioral, visuospatial and language impairments. Other major components of AD pathology are the presence of amyloid plaques and neurofibrillary tangles. Patients with AD have amyloid deposits in areas such as the limbic cortex, basal forebrain, LANGUAGE AND COMMUNICATION DEFICITS IN ALZHEIMER’S 6 substantia nigra, raphe nuclei, locus coeruleus and in cerebral arterioles. These extracellular neuritic plaques can effectively disrupt communication between nerve cells. The neurofibrillary tangles observed in pathological AD patients have a distinct “paired helical structure and are quantitatively highly correlated with dementia severity” (Reilly, 2011, p.18). The neurofibrillary pathology of AD begins in the medial perirhinal cortex (mPRC) before spreading to the entorhinal cortex and hippocampus in the anterior medial temporal lobe (mMTL; Hirni et al., 2013). Such tangles consist of the hyperphosphorylated proteins tau and ubiquitin, which actively disrupt memory systems in the brain leading to memory loss and potentially neuronal death. Another major hallmark of pathological AD is widespread cortical neuronal loss. This is seen predominantly in the hippocampus, temporal neocortex and in the basal forebrain nuclei, as well as in several subcortical structures as well. Lastly, synaptic destruction is another indicator of pathological AD. In fact, synaptic destruction may be the major proximate cause of early cognitive decline (Reilly, 2011). These pathological components of AD are the underlying mechanisms responsible for the manifestations of the disease observed in patients’ daily lives. Progressive memory dysfunction may be the most apparent, but other notable effects of AD pathology include amnesia, aphasia, agnosia, apraxia, and prominent visuospatial impairment. The cognitive decline observed in individuals with AD often involves issues with working memory functioning. Dynamic interactions between different brain regions cause working memory to play a huge role in temporary information processing and guiding behaviors in daily life. Specifically, the prefrontal cortex and the parietal cortex are critical regions in working memory functioning. Eriksson and colleagues