Semantic processing and neurobiology in Alzheimer's disease and Mild Cognitive Impairment

Abstract

In the present theoretical review we will perform a critical surveillance of linguistic and semantic processing in Mild Cognitive Impairment and Alzheimer's disease, explicitly favouring a neurobiological prism. We conjecture that most linguistic alterations arise from semantic indiscrimination through inhibitory hypofunction. Specifically, a conjoint cluster of cholinergic dysfunction, Aβ load and somatostatin-positive cell loss renders the semantic network disinhibited and overly noisy: fine discriminatory processes in temporal and medial-frontal regions cannot differentiate semantic representations from baseline unconscious activity, which leads to failures in faithful retrieval (preferentially idiosyncratic lexical-semantic links, e.g., proper names), verbal fluency anomalies, semantic interference, dampened N400 effects, and various semiological deviances.

Keywords: Alzheimer's disease; Dementia; Disinhibition; Language; Mild cognitive impairment; N400; Semantic memory.