Neuroanatomical foundations of naming impairments across different neurologic conditions

Abstract

The ability to name objects or abstract entities is an essential feature of speech and language, being commonly considered a central component of normal neurologic function. For this reason, the bedside testing of naming performance is part of the neurologic examination, especially since naming impairments can signify the early onset of a progressive disease or the occurrence of a more established problem. Modern neuroscience research suggests that naming relies on specific and distributed networks that operate in concert to support various processing stages, spanning from object recognition to spoken words. Likewise, studies evaluating the types of naming impairments in patients with neurologic conditions have contributed to the understanding of acquired forms of naming impairments and the underlying stages during normal language processing. In this article, we review the neurobiological mechanisms supporting naming, with a focus on the clinical application of these concepts. We provide an overview of the stages of cognitive processing that are hypothesized to support naming. For each stage, we explore the evidence revealing its neural basis, drawing parallels to clinical syndromes that commonly disrupt each stage. We review the patterns of naming impairment across various neurologic conditions, including classic language disorders, such as poststroke aphasia or primary progressive aphasia, as well as other diseases where language impairments may be subtle but helpful for the appropriate diagnosis. In this context, we provide a structured and practical guide for the bedside naming assessments rooted in modern neuroscience, aimed at supporting the evaluation and diagnosis of neurologic conditions that affect language. Neurology ® 2015;85:284-292 GLOSSARY AD 5 Alzheimer disease; AoS 5 apraxia of speech; FTLD 5 frontotemporal lobar degeneration; PCA 5 posterior cortical atrophy; PPA-L 5 logopenic variant of primary progressive aphasia; PPA-S 5 semantic variant of primary progressive aphasia; TLE 5 temporal lobe epilepsy; TOT 5 tip of the tongue.The ability to name objects or abstract entities is essential in everyday speech production. Retrieving the correct word that denotes a specific something relies on an orchestrated sequence of brain processes, ranging from perception of a stimulus to the physical articulation of the sounds used to speak its name. While intimately related, each stage of this complex process relies on the activation of distinct neural circuits. Accordingly, naming impairments may emerge following disruption of one or more of the stages thought to support naming.The process of naming most commonly occurs during discourse, when we are constantly required to retrieve abstract concepts to either understand or deliver a message, or by our need to identify an object perceived in the environment. Thus, naming can relate to an object that was seen, smelled, touched, heard, tasted, or any combination of these modalities. Stimulus processing results in the recognition of the stimulus as a famil...

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