Acquired Language Disorders: Aphasia in Adults

Aphasia is an acquired impairment of language caused by damage to the brain regions that support it, most often after a stroke. Unlike developmental language disorders, aphasia disrupts a previously intact language system, affecting speaking, understanding, reading, and writing to varying degrees while leaving general intelligence largely intact.

Definition

Aphasia is an acquired language disorder resulting from focal or diffuse brain injury - typically to left-hemisphere perisylvian regions - that impairs the production or comprehension of spoken and written language across one or more modalities, in a person who had previously acquired language normally.

Scope

This entry covers the definition of acquired aphasia, the classical syndromes and the brain regions implicated, the principal causes, and the evidence base for speech and language therapy. It is a reference description of the disorder and the rehabilitation literature, not individualized clinical guidance.

Core questions

• How does acquired aphasia differ from developmental language disorder?
• What distinguishes fluent from non-fluent aphasia syndromes?
• Which brain regions are most associated with language impairment?
• What does the evidence say about speech and language therapy after stroke?

Key concepts

• Non-fluent (Broca-type) versus fluent (Wernicke-type) aphasia
• Perisylvian language network and left-hemisphere dominance
• Spontaneous recovery and the role of therapy intensity
• Anomia and word-finding difficulty
• Global, conduction, and transcortical syndromes
• Aphasia versus dysarthria and apraxia of speech

Mechanisms

Aphasia arises when injury - most commonly ischaemic or haemorrhagic stroke, but also tumour, trauma, or neurodegeneration - damages the left-hemisphere perisylvian language network or its connections. Lesion location influences the syndrome: anterior damage tends to produce effortful, non-fluent output with relatively preserved comprehension, while posterior damage tends to produce fluent but error-laden speech with impaired comprehension, though real cases rarely fit the textbook categories cleanly. Some spontaneous recovery occurs as the brain reorganises, and rehabilitation aims to support and extend this process.

Clinical relevance

Aphasia is a leading communication consequence of stroke and a major focus of adult speech-language pathology and neurorehabilitation, with substantial effects on independence, social participation, and mood. This entry summarises the disorder and the evidence base; it does not prescribe assessment or therapy for any individual, which requires professional clinical management.

Epidemiology

Aphasia occurs in a substantial proportion of people in the acute period after stroke, and because stroke incidence rises with age, acquired aphasia is concentrated in older adults. Its overall burden tracks the epidemiology of cerebrovascular disease, as reviewed by Berthier.

History

The study of aphasia founded much of cognitive neuroscience: Paul Broca's 1861 and Carl Wernicke's 1874 case-lesion correlations linked specific language functions to specific cortical regions and established left-hemisphere language dominance. The classical syndrome framework was formalised in the twentieth century through assessment batteries such as that of Goodglass and Kaplan. More recent work has refined and partly challenged the localizationist model and built the controlled-trial evidence base for therapy, synthesised in the Cochrane reviews by Brady and colleagues.

Debates

Does speech and language therapy improve aphasia outcomes?

Cochrane evidence indicates speech and language therapy can benefit functional communication after stroke, but questions remain about the optimal intensity, timing, and dose, and about which patients benefit most.

How well do classical syndromes describe real patients?

The Broca and Wernicke localization model is a useful teaching framework, but many patients do not fit a single syndrome and lesion-symptom relationships are more distributed than the classical picture implies.

Key figures

• Paul Broca
• Carl Wernicke
• Harold Goodglass
• Edith Kaplan
• Marcelo Berthier

Seminal works

• brady-2016
• goodglass-2001

Frequently asked questions

Does aphasia mean a loss of intelligence?

No. Aphasia impairs the use and understanding of language, but general intelligence and knowledge are typically preserved; the person knows what they want to say but cannot access or produce the language to say it.

What is the most common cause of aphasia?

Stroke is the most common cause, particularly stroke affecting the left hemisphere. Aphasia can also follow head injury, brain tumours, or certain neurodegenerative diseases.