According to the WHO, neurodegenerative disorders (NDs) are a group of conditions that affect the neurons in the human brain and nervous system[1]. Examples of NDs include Alzheimer’s disease, PD, or Huntington’s disease. Although certain therapies may help relieve some of the physical or cognitive symptoms associated with NDs, slowing their progression, a permanent solution doesn’t exist, as a concecuence they instill a substantial degree of anxiety and powerlessness to individuals affected by them. Therefore, their study poses a major challenge to the development of effective treatments and interventions. The main affectations that can manifest predomintantly relate to movement or cognitive functions, this serves to broadly classify the different disorders as neuromotor or neurocognitive depending on the dysfunctions may they cause.
The study of NDs is as long as humans have been recording history. The understanding and categorization of these disorders have evolved over time, gradually unravelling their intricate nature. The earliest observations of these disorders date back to ancient civilizations. For instance, descriptions of dementia-like symptoms can be found in ancient Egyptian, Greek, and Roman texts (Boller and Forbes, 1998, Papavramidou, 2018). Alzheimer’s disease, the most prevalent form of dementia, was named after Dr. Alois Alzheimer, who in 1906 identified unique brain abnormalities in a patient exhibiting severe memory loss and cognitive decline. The latter half of the 20th century witnessed significant breakthroughs in molecular biology and genetics, which revolutionised the study of NDs and their characterization. The identification of specific genes associated with inherited forms of NDs, such as Huntington’s disease, allowed for deeper insights into the underlying mechanisms.
Despite extensive research efforts, effective treatments to halt or reverse the progression of NDs remain elusive. However, various therapeutic approaches, including medication, physical therapy, and supportive care, have been developed to alleviate symptoms and enhance the quality of life for individuals affected by these disorders (Kalaria et al., 2004; Nussbaum, 2013, Blom, Emmelot-Vonk, and Koek, 2013). So far exploring potential biomarkers, developing novel therapeutic targets, and investigating strategies such as stem cell therapy and gene editing techniques in the pursuit of finding more effective treatments and ultimately discovering a cure (Emamzadeh and Surguchov, 2018). A brief description of the most prevalent NDs is given in Table 1.
| Brief description of the most prevalent NDs | |
| Disorder | Description |
| Alzheimer’s disease | Alzheimer’s disease is a complex neurodegenerative disorder characterized by the gradual and irreversible decline of cognitive functions, particularly memory and thinking abilities. While the exact causes of Alzheimer’s disease are not fully understood, there are several recognized underlying factors that involve a complex interplay of genetic, environmental, and lifestyle choices. Accumulation of abnormal protein deposits, such as beta-amyloid plaques and tau tangles, in the brain is a hallmark of this disease. |
| Parkinson’s disease | PD is a neurodegenerative disorder characterized by the progressive loss of dopamine-producing cells in a region of the brain called the substantia nigra. The exact causes of PD are not fully understood, but there are several recognized underlying factors, combination of genetic and environmental factors, as well as the accumulation of abnormal alpha-synuclein protein, are believed to contribute to its development. |
| Huntington’s disease | Huntington’s disease is an inherited neurodegenerative disorder caused by a mutation in the huntingtin gene. The mutation leads to the production of a toxic protein that damages nerve cells in the brain, particularly in the BG. |
| Amyotrophic lateral sclerosis | It is characterised by the degeneration of motor neurons, which are responsible for controlling voluntary muscle movements. Most cases of amyotrophic lateral sclerosis are sporadic, with no clear cause, while a small percentage is associated with specific genetic mutations. |
| Multiple sclerosis | Multiple sclerosis is an autoimmune disease where the immune system mistakenly attacks the protective covering of nerve fibres in the central nervous system. The exact cause of MS is unknown, but it is thought to involve a combination of genetic and environmental factors. |
| Frontotemporal dementia | Frontotemporal dementia is a group of disorders characterised by the degeneration of nerve cells in the frontal and temporal lobes of the brain. It can be caused by genetic mutations or occur sporadically without a known cause. |
| Lewy body dementia (LBD) | Lewy body’s dementia is associated with the buildup of abnormal protein deposits called Lewy bodies in the brain. The exact cause is unknown, but it is believed to involve a combination of genetic and environmental factors. |
| Creutzfeldt-Jakob disease | Creutzfeldt-Jakob’s disease is a rare degenerative brain disorder caused by the abnormal folding of prion proteins. It can occur spontaneously, be inherited, or transmitted through exposure to infected tissues. |
[1] https://www.nature.com/subjects/neurodegenerative-diseases.
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Time-frequency representations in speech perception
Nowadays applications demand a comprehensive view of voice and speech perception to build more complex and competitive procedures amenable of extracting as much knowledge from sound-based human communication as possible. Many knowledge-extraction tasks from speech and voice may share signal treatment procedures which can be devised under the point of view of bio-inspiration. The present paper examines a hierarchy of sound processing functionalities at the auditory and perceptual levels on the Auditory Neural pathways which can be translated into bio-inspired speech-processing techniques, their fundamental characteristics being analyzed in relation with current tendencies in cognitive audio processing. The pathways linking the peripheral auditory system (cochlear complex) with the brain cortex are briefly examined, with special attention to the study of neuronal structures showing specific capabilities under the point of view of formant analysis and the build-up of a semantic hierarchy from the time-frequency structure of speech to explore their capability of conveying semantics to speech processing and understanding from the minimal acoustic clues with elementary meaning or ‘‘sematoms’’. The replication of known biological functionality by algorithmic methods through bio-inspiration is a secondary aim of the research. Examples extracted from speech processing tasks in the domain of acoustic-phonetics are presented. These may find applicability in speech recognition, speaker’s characterization and biometry, emotion detection, and others related.
Neuromorphic detection of speech dynamics
Speech and voice technologies are experiencing a profound review as new paradigms are sought to overcome some specific problems which cannot becompletely solved by classical approaches. Neuromorphic Speech Processing is an emerging area in which research is turning the face to understand the natural neural processing of speech by the Human Auditory System in order to capture the basic mechanisms solving difficult tasks in an efficient way. In the present paper a further step ahead is presented in the approach to mimic basic neural speech processing by simple neuromorphic units standing on previous work to show how formant dynamics –and henceforth consonantal features– can be detected by using a general neuromorphic unit which can mimic the functionality of certain neurons found in the upper auditory pathways. Using these simple building blocks a General Speech Processing Architecture can be synthesized as a layered structure. Results from different simulation stages are
provided as well as a discussion on implementation details. Conclusions and future work are oriented to
describe the functionality to be covered in the next research steps.