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Almeida VN. Somatostatin and the pathophysiology of Alzheimer's disease. Ageing Res Rev 2024; 96:102270. [PMID: 38484981 DOI: 10.1016/j.arr.2024.102270] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Revised: 03/09/2024] [Accepted: 03/09/2024] [Indexed: 03/28/2024]
Abstract
Among the central features of Alzheimer's disease (AD) progression are altered levels of the neuropeptide somatostatin (SST), and the colocalisation of SST-positive interneurons (SST-INs) with amyloid-β plaques, leading to cell death. In this theoretical review, I propose a molecular model for the pathogenesis of AD based on SST-IN hypofunction and hyperactivity. Namely, hypofunctional and hyperactive SST-INs struggle to control hyperactivity in medial regions in early stages, leading to axonal Aβ production through excessive presynaptic GABAB inhibition, GABAB1a/APP complex downregulation and internalisation. Concomitantly, excessive SST-14 release accumulates near SST-INs in the form of amyloids, which bind to Aβ to form toxic mixed oligomers. This leads to differential SST-IN death through excitotoxicity, further disinhibition, SST deficits, and increased Aβ release, fibrillation and plaque formation. Aβ plaques, hyperactive networks and SST-IN distributions thereby tightly overlap in the brain. Conversely, chronic stimulation of postsynaptic SST2/4 on gulutamatergic neurons by hyperactive SST-INs promotes intense Mitogen-Activated Protein Kinase (MAPK) p38 activity, leading to somatodendritic p-tau staining and apoptosis/neurodegeneration - in agreement with a near complete overlap between p38 and neurofibrillary tangles. This model is suitable to explain some of the principal risk factors and markers of AD progression, including mitochondrial dysfunction, APOE4 genotype, sex-dependent vulnerability, overactive glial cells, dystrophic neurites, synaptic/spine losses, inter alia. Finally, the model can also shed light on qualitative aspects of AD neuropsychology, especially within the domains of spatial and declarative (episodic, semantic) memory, under an overlying pattern of contextual indiscrimination, ensemble instability, interference and generalisation.
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Affiliation(s)
- Victor N Almeida
- Institute of Psychiatry, Faculty of Medicine, University of São Paulo (USP), Brazil; Faculty of Languages, Federal University of Minas Gerais (UFMG), Brazil.
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Clark CN, Golden HL, McCallion O, Nicholas JM, Cohen MH, Slattery CF, Paterson RW, Fletcher PD, Mummery CJ, Rohrer JD, Crutch SJ, Warren JD. Music models aberrant rule decoding and reward valuation in dementia. Soc Cogn Affect Neurosci 2018; 13:192-202. [PMID: 29186630 PMCID: PMC5827340 DOI: 10.1093/scan/nsx140] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 11/06/2017] [Accepted: 11/19/2017] [Indexed: 01/03/2023] Open
Abstract
Aberrant rule- and reward-based processes underpin abnormalities of socio-emotional behaviour in major dementias. However, these processes remain poorly characterized. Here we used music to probe rule decoding and reward valuation in patients with frontotemporal dementia (FTD) syndromes and Alzheimer's disease (AD) relative to healthy age-matched individuals. We created short melodies that were either harmonically resolved ('finished') or unresolved ('unfinished'); the task was to classify each melody as finished or unfinished (rule processing) and rate its subjective pleasantness (reward valuation). Results were adjusted for elementary pitch and executive processing; neuroanatomical correlates were assessed using voxel-based morphometry. Relative to healthy older controls, patients with behavioural variant FTD showed impairments of both musical rule decoding and reward valuation, while patients with semantic dementia showed impaired reward valuation but intact rule decoding, patients with AD showed impaired rule decoding but intact reward valuation and patients with progressive non-fluent aphasia performed comparably to healthy controls. Grey matter associations with task performance were identified in anterior temporal, medial and lateral orbitofrontal cortices, previously implicated in computing diverse biological and non-biological rules and rewards. The processing of musical rules and reward distils cognitive and neuroanatomical mechanisms relevant to complex socio-emotional dysfunction in major dementias.
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Affiliation(s)
- Camilla N Clark
- Dementia Research Centre, UCL Institute of Neurology, University College London, London, UK
| | - Hannah L Golden
- Dementia Research Centre, UCL Institute of Neurology, University College London, London, UK
| | - Oliver McCallion
- Oxford University Clinical Academic Graduate School, University of Oxford, Oxford, UK
| | - Jennifer M Nicholas
- Dementia Research Centre, UCL Institute of Neurology, University College London, London, UK
- London School of Hygiene and Tropical Medicine, University of London, London, UK
| | - Miriam H Cohen
- Dementia Research Centre, UCL Institute of Neurology, University College London, London, UK
| | - Catherine F Slattery
- Dementia Research Centre, UCL Institute of Neurology, University College London, London, UK
| | - Ross W Paterson
- Dementia Research Centre, UCL Institute of Neurology, University College London, London, UK
| | - Phillip D Fletcher
- Dementia Research Centre, UCL Institute of Neurology, University College London, London, UK
| | - Catherine J Mummery
- Dementia Research Centre, UCL Institute of Neurology, University College London, London, UK
| | - Jonathan D Rohrer
- Dementia Research Centre, UCL Institute of Neurology, University College London, London, UK
| | - Sebastian J Crutch
- Dementia Research Centre, UCL Institute of Neurology, University College London, London, UK
| | - Jason D Warren
- Dementia Research Centre, UCL Institute of Neurology, University College London, London, UK
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Sandberg C, Sebastian R, Kiran S. Typicality mediates performance during category verification in both ad-hoc and well-defined categories. JOURNAL OF COMMUNICATION DISORDERS 2012; 45:69-83. [PMID: 22261305 PMCID: PMC3298749 DOI: 10.1016/j.jcomdis.2011.12.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2011] [Revised: 12/08/2011] [Accepted: 12/13/2011] [Indexed: 05/03/2023]
Abstract
BACKGROUND The typicality effect is present in neurologically intact populations for natural, ad-hoc, and well-defined categories. Although sparse, there is evidence of typicality effects in persons with chronic stroke aphasia for natural and ad-hoc categories. However, it is unknown exactly what influences the typicality effect in this population. AIMS The present study explores the possible contributors to the typicality effect in persons with aphasia by analyzing and comparing data from both normal and language-disordered populations, from persons with aphasia with more semantic impairment versus those with less semantic impairment, and from two types of categories with very different boundary structure (ad-hoc vs. well-defined). METHODS AND PROCEDURES A total of 40 neurologically healthy adults (20 older, 20 younger) and 35 persons with aphasia (20 LSI (less-semantically impaired) patients, 15 MSI (more-semantically impaired) patients) participated in the study. Participants completed one of two tasks: either category verification for ad-hoc categories or category verification for well-defined categories. OUTCOMES AND RESULTS Neurologically healthy participants showed typicality effects for both ad-hoc and well-defined categories. MSI patients showed a typicality effect for well-defined categories, but not for ad-hoc categories, whereas LSI patients showed a typicality effect for ad-hoc categories, but not for well-defined categories. CONCLUSIONS These results suggest that the degree of semantic impairment mediates the typicality effect in persons with aphasia depending on the structure of the category. LEARNING OUTCOMES After reading this article, the reader should be able to: (1) Describe the typicality effect and in which populations it occurs. (2) Explain how the typicality effect might change depending on category structure. (3) summarize how semantic impairment influences category representation and/or access.
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Affiliation(s)
- Chaleece Sandberg
- Department of Speech, Language, and Hearing Sciences, Sargent College of Health and Rehabilitation Sciences, Boston University, 635 Commonwealth Avenue, Boston, MA 02215, USA.
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Reilly J, Peelle JE, Antonucci SM, Grossman M. Anomia as a marker of distinct semantic memory impairments in Alzheimer's disease and semantic dementia. Neuropsychology 2011; 25:413-26. [PMID: 21443339 PMCID: PMC3125450 DOI: 10.1037/a0022738] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
OBJECTIVE Many neurologically constrained models of semantic memory have been informed by two primary temporal lobe pathologies: Alzheimer's disease (AD) and Semantic Dementia (SD). However, controversy persists regarding the nature of the semantic impairment associated with these patient populations. Some argue that AD presents as a disconnection syndrome in which linguistic impairment reflects difficulties in lexical or perceptual means of semantic access. In contrast, there is a wider consensus that SD reflects loss of core knowledge that underlies word and object meaning. Object naming provides a window into the integrity of semantic knowledge in these two populations. METHOD We examined naming accuracy, errors and the correlation of naming ability with neuropsychological measures (semantic ability, executive functioning, and working memory) in a large sample of patients with AD (n = 36) and SD (n = 21). RESULTS Naming ability and naming errors differed between groups, as did neuropsychological predictors of naming ability. Despite a similar extent of baseline cognitive impairment, SD patients were more anomic than AD patients. CONCLUSIONS These results add to a growing body of literature supporting a dual impairment to semantic content and active semantic processing in AD, and confirm the fundamental deficit in semantic content in SD. We interpret these findings as supporting of a model of semantic memory premised upon dynamic interactivity between the process and content of conceptual knowledge.
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Affiliation(s)
- Jamie Reilly
- Department of Speech, Language, and Hearing Sciences, University of Florida, Gainesville, FL 32610, USA.
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González-Nosti M, Arango-Lasprilla JC, Cuetos F. The generation effect in patients with mild cognitive impairment. Am J Alzheimers Dis Other Demen 2010; 25:576-84. [PMID: 20930187 PMCID: PMC10845521 DOI: 10.1177/1533317510382284] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2024]
Abstract
The generation effect (GE) has been proven as an effective technique to improve learning and memory in healthy and clinical populations. However, it has not been found with meaningless materials such as pseudowords. Several hypotheses postulate the participation of semantic memory in the information-generating process. There is indeed a clear decrease in the effect in patients with serious semantic memory disorders, such as Alzheimer's disease (AD) but, if this is correct, other patients whose memory disorders are not so serious, such as mild cognitive impairment (MCI), should show GE to some extent. To test this hypothesis, we examined 54 participants (18 healthy adults, 18 patients with AD, and 18 with MCI) in a task involving reading and completion of phrases. Results show a decreased (although obvious) GE in patients with MCI. Likewise, results indicate that greater semantic damage will lead to poorer performance with less familiar stimuli or low-frequency words.
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Kincses TZ, Chadaide Z, Varga ET, Antal A, Paulus W. Task-related temporal and topographical changes of cortical activity during ultra-rapid visual categorization. Brain Res 2006; 1112:191-200. [PMID: 16928365 DOI: 10.1016/j.brainres.2006.07.044] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2005] [Revised: 06/25/2006] [Accepted: 07/05/2006] [Indexed: 11/17/2022]
Abstract
The aim of our study was to provide electrophysiological evidence about the modulation of the categorization process by task requirements in the human brain. Event-related potentials (ERP) were recorded during three different categorization tasks using matched stimulus sets. In all cases, the subjects were required to differentiate between "animal" and "non-animal" stimuli. In the first task (two-choice task), they were asked to press corresponding buttons to each stimulus types. The second task was a go/no-go paradigm, only animal stimuli required motor response. The third task was a counting task; participants had to count the animal stimuli without any motor response. The reaction times in the go/no-go paradigm were significantly shorter. ERP differences between animal and non-animal pictures in the go/no-go task also appeared earlier and were localized at more posterior scalp positions compared to the two-choice task. Comparing animal responses in the two-choice task and in the go/no-go paradigm, we found a significant difference in the 130- to 170-ms time window over the fronto-central, centro-parietal regions. Similar differences were found between the responses to animal pictures in the two-choice task and in the counting paradigm. We used brain electric source analysis (BESA) algorithm on difference waves to localize the best fitting dipoles and determine the localization of brain areas contributing to scalp potential differences. The results show that different task requirements evoke different activity in the medial part of the temporal pole. The data we provided here draw attention to the careful handling of results obtained from categorization experiments, because different task requirements can affect the early categorization process itself.
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Lind J, Persson J, Ingvar M, Larsson A, Cruts M, Van Broeckhoven C, Adolfsson R, Bäckman L, Nilsson LG, Petersson KM, Nyberg L. Reduced functional brain activity response in cognitively intact apolipoprotein E ε4 carriers. Brain 2006; 129:1240-8. [PMID: 16537568 DOI: 10.1093/brain/awl054] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The apolipoprotein E epsilon4 (APOE epsilon4) is the main known genetic risk factor for Alzheimer's disease. Genetic assessments in combination with other diagnostic tools, such as neuroimaging, have the potential to facilitate early diagnosis. In this large-scale functional MRI (fMRI) study, we have contrasted 30 APOE epsilon4 carriers (age range: 49-74 years; 19 females), of which 10 were homozygous for the epsilon4 allele, and 30 non-carriers with regard to brain activity during a semantic categorization task. Test groups were closely matched for sex, age and education. Critically, both groups were cognitively intact and thus symptom-free of Alzheimer's disease. APOE epsilon4 carriers showed reduced task-related responses in the left inferior parietal cortex, and bilaterally in the anterior cingulate region. A dose-related response was observed in the parietal area such that diminution was most pronounced in homozygous compared with heterozygous carriers. In addition, contrasts of processing novel versus familiar items revealed an abnormal response in the right hippocampus in the APOE epsilon4 group, mainly expressed as diminished sensitivity to the relative novelty of stimuli. Collectively, these findings indicate that genetic risk translates into reduced functional brain activity, in regions pertinent to Alzheimer's disease, well before alterations can be detected at the behavioural level.
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Affiliation(s)
- Johanna Lind
- Department of Clinical Neuroscience, MR Research Center, Karolinska Hospital N-8, Stockholm, Sweden.
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Moelter ST, Hill SK, Hughett P, Gur RC, Gur RE, Ragland JD. Organization of semantic category exemplars in schizophrenia. Schizophr Res 2005; 78:209-17. [PMID: 16002266 PMCID: PMC4337816 DOI: 10.1016/j.schres.2005.06.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/06/2005] [Revised: 06/06/2005] [Accepted: 06/13/2005] [Indexed: 11/28/2022]
Abstract
Semantic memory was investigated in 27 individuals with schizophrenia and 30 healthy controls using an animal similarity judgment and organization test with reduced retrieval demands. Participants arranged 12 common animal names according to similarity on a computer screen and provided verbal descriptions of organizational strategies. Distance between each animal pair was compared to the number of shared semantic attributes between the pairs (e.g., size, diet, habitat). The three primary organizational strategies included single animals not related to other exemplars, isolated clusters of animals that shared a single strategic relationship (e.g., pets), and overlapping clusters that combined more than one strategic relationship (e.g., cats and mammals). A strong negative correlation was observed between distance ratings and number of shared semantic attributes, confirming that semantic features related to visual distances in both groups. Animal pairs that shared few semantic attributes were placed in closer proximity in the schizophrenia group, whereas the groups placed animal pairs sharing more features equidistantly. Analyses of clustering strategies revealed a double dissociation, with patients relying on isolated, non-overlapping clusters and controls producing more overlapping semantic clusters. Results suggest that performance differences on semantic tasks with limited retrieval demands in schizophrenia relate to difficulties utilizing higher-order categorization strategies.
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Affiliation(s)
- Stephen T Moelter
- University of the Sciences in Philadelphia, 600 South 43rd Street, Philadelphia, PA 19104, USA.
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Ko PC, Kilduff PT, Higgens JA, Milberg W, McGlinchey R. Evidence for Intact Selective Attention in Alzheimer's Disease Patients Using a Location Priming Task. Neuropsychology 2005; 19:381-9. [PMID: 15910124 DOI: 10.1037/0894-4105.19.3.381] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Researchers examining selective attentional mechanisms in patients with Alzheimer's disease (AD) often report impairment in patients' ability to inhibit irrelevant or distracting information. However, in many studies reporting such failures, researchers used tasks that require semantic processing, which a large body of literature documents to be disrupted in AD. The authors of this study used a spatial location-priming task that minimized semantic processing to examine the phenomena of negative priming and facilitative priming in 13 AD patients and 13 healthy older adults. AD patients demonstrated facilitative and negative priming proportionately equivalent to that of older adults. These findings suggest that both the facilitative and inhibitory mechanisms involved in selective attention are preserved in patients with AD and can be revealed in tasks that minimize semantic processing.
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Affiliation(s)
- Philip C Ko
- Geriatric Neuropsychology Laboratory, New England Geriatric Research, Education, and Clinical Center (GRECC), Veterans Affairs Boston Healthcare System, Boston, MA 02130, USA
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