Relatively spared during most of the timeline of normal ageing, semantic memory shows a subtle yet measurable decline even during the preclinical stage of Alzheimer's disease (AD). This decline is thought to reflect early neurofibrillary changes and impairment is detectable using tests of language relying on lexical-semantic abilities. A promising approach is the characterisation of semantic parameters such as typicality and age of acquisition of words, and propositional density from verbal

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... ut. Seminal research like the Nun Study or the analysis of the linguistic decline of famous writers and politicians later diagnosed with AD supports the early diagnostic value of semantic processing and semantic memory. Moreover, measures of these skills may play an important role for the prognosis of patients with mild cognitive impairment. Executive Summary The quest for an early biomarker of Alzheimer's disease (AD) is paramount  Pathophysiological markers of AD do not always reflect the clinical profile.  The current diagnostic formulae are centred on the early symptomatic prodromal stages of AD.  A cognitive marker centred on semantic memory decline could be the most valid route to detect preclinical AD. Semantic memory changes differ in normal ageing and AD  Semantic processing and semantic memory tend to be relatively preserved in normal ageing.  A severe semantic decline is observed in AD since its earliest stages. Tests of language as a central typology of tests for an early diagnosis of AD  The organisational complexity of semantic processing is quite intricate, both at a computational and neural level.  Language tests are the most common instruments to test semantic processing.  Distinctive instruments such as the Boston Naming test or the Category Fluency test are helpful instruments to detect early semantic changes. Tests of semantic abilities as a diagnostic and prognostic marker  The analysis of verbal production of famous writers and politicians later diagnosed with AD strongly suggests that semantic changes are measurable during the preclinical stage.  Semantic competence appears informative at predicting disease progression of patients with mild cognitive impairment. 5 Conclusions  Conceiving semantic memory and semantic processing as the primary focus of diagnostic and prognostic paradigms for AD is based on neuroanatomical and neuropathological evidence.  An approach centred on semantic memory and semantic processing could be fruitful and revolutionary. 6 Future Perspective Indices of semantic processing could be valid and reliable measures in clinical settings for the preclinical detection of early changes associated with Alzheimer's disease (AD). A number of measures may be easily identified in compliance with ideal parametric properties, for single one-off measurements as well as for repeated measurements over time. Measures of semantic processing could also be at the centre of the diagnostic procedures to stratify patients for enrolment in clinical trials. The implementation of tests of semantic processing can be converted into safe and costeffective screening instruments to detect individuals at risk of developing AD. Comparable screening instruments need to be designed for use in non specialist settings by medical staff who have minimal or no competence with the administration of cognitive tests.