Stroke and IQ: How Much Intelligence Can a Stroke Take Away?

There is no single figure for stroke IQ loss, because a stroke damages specific regions of the brain and the abilities those regions support. About half of stroke survivors show some cognitive impairment in the months after the event, yet one person may lose language while keeping strong reasoning, and another may struggle with visual tasks while speaking fluently.

A stroke happens when blood flow to part of the brain is blocked (an ischaemic stroke) or a blood vessel bursts (a haemorrhagic stroke). This page covers how common thinking problems are after a stroke, why the location of the damage shapes the test profile, why brief screening tests and full IQ testing answer different questions, how cognition changes in the years after a stroke, and what is known about stroke in childhood.

Cognitive problems are among the most frequent consequences of stroke. Barbay and colleagues pooled 16 hospital-based studies with 3,087 patients and found that 53.4% of survivors had a post-stroke neurocognitive disorder. About two-thirds of those cases were mild (36.4% of all patients) and about one-third were major (16.5%), the level that corresponds to dementia.

The Stroke and Cognition Consortium (STROKOG) took a different approach. Lo and colleagues harmonised individual test data from 13 studies in 8 countries, covering 3,146 people tested 2 to 6 months after a stroke or transient ischaemic attack. They found that 44% were impaired in global cognition and 30% to 35% were impaired in any single domain, such as memory, language or attention.

Dementia is the severe end of this range. In a meta-analysis of 30 cohorts, Pendlebury and Rothwell estimated that about 10% of patients had dementia before their first stroke, about 10% developed new dementia soon after a first stroke, and more than a third had dementia after a recurrent stroke. Our article on whether IQ is correlated with dementia covers how earlier ability relates to later decline.

IQ tests combine many abilities into one score, while a stroke usually damages one side of the brain and one vascular territory. The result is an uneven profile. In a classic study of 656 patients with damage to one hemisphere, Warrington and colleagues found that Verbal IQ on a shortened Wechsler scale was lower in every left-hemisphere group than in the matching right-hemisphere group. Performance IQ was lowered mainly when the right parietal lobe was involved.

Two common stroke syndromes show why a single number misleads. "Aphasia" is a loss of language ability, and in a population study in Basel, 30% of people with a first ischaemic stroke had it. A person with aphasia may be unable to define words or explain similarities, so verbal subtests end up measuring the language damage while the reasoning underneath goes unmeasured. "Spatial neglect" is a failure to notice one side of space, usually the left. Esposito and colleagues' review of 41 studies put its rate at about 30% after a stroke affecting one side, 38% after right-hemisphere damage and 18% after left-hemisphere damage. Someone with neglect can miss half of a visual puzzle and score poorly on nonverbal items for reasons unrelated to reasoning.

Motor weakness adds another layer. Many IQ subtests are timed or require handling materials, and a weak dominant hand slows performance. A full-scale score that blends these effects can sit in the average range while hiding a severe, specific loss, or look low when much of the person's reasoning is intact.

Most stroke services start with brief screening tools, and full IQ tests are uncommon. The Mini-Mental State Examination (MMSE) was designed with dementia in mind, and it often misses the problems stroke causes. In the Oxford Vascular Study, Pendlebury and colleagues gave both the MMSE and the Montreal Cognitive Assessment (MoCA) to 413 testable patients after a stroke or transient ischaemic attack. Seventy per cent scored below the MoCA cut-off, and 162 of them scored in the normal range on the MMSE. Their missed deficits were in delayed recall, abstraction, visuospatial and executive function, and sustained attention.

The same study shows a quieter problem. Of 493 patients, 16% could not be tested at all, and those patients were older and often had dysphasia (a language impairment) or dementia. People with the most severe effects are the ones least likely to appear in test-based statistics.

A full assessment by a neuropsychologist goes further than a screen. It measures each domain separately, chooses tests that work around aphasia or a weak hand, and compares current scores with an estimate of the person's ability before the stroke. Because pre-stroke IQ scores are rarely on record, clinicians estimate them from education, occupation and reading tests; our page on IQ and traumatic brain injury explains how premorbid IQ estimation works.

Speed of treatment matters because brain tissue dies quickly. Saver calculated that in a typical large-vessel ischaemic stroke, about 1.9 million neurons are lost each minute without treatment, and the brain ages about 3.6 years for each hour of delay. That is why stroke is treated as an emergency, and why outcomes vary so much between people with similar strokes.

After the first months, cognition tends to settle. Del Ser and colleagues assessed 193 patients without previous dementia at 3 months and followed them to 24 months. Cognitive status was stable in 78.2%, worse in 14% and better in 7.8%. Older age and cognitive decline before the stroke predicted progression.

Over longer periods, a stroke can change the slope of decline as well as the starting point. Levine and colleagues followed 23,572 adults aged 45 and older in the US REGARDS cohort, 515 of whom survived a new stroke. Stroke was linked to an immediate drop in global cognition, new learning and verbal memory, followed by faster decline in global cognition and executive function than before the stroke, a pattern that persisted across about 6 years of follow-up. Pendlebury and Rothwell found that after the first year, new dementia accumulated at about 3% per year in hospital-based studies, only a little more than recurrent strokes alone would explain. Because post-stroke dementia was so strongly tied to multiple strokes, the authors pointed to preventing further strokes as a likely way to reduce it.

Strokes also occur in newborns and children, and the developing brain is not automatically protected. Westmacott and colleagues tested 145 children who had a stroke affecting one side of the brain, at ages ranging from the newborn period to 16 years, using age-appropriate Wechsler scales. As a group, the children scored significantly below the test norms on overall intelligence, verbal ability, working memory and processing speed. Those whose stroke occurred around birth scored lower than the older groups on most measures.

Other outcomes complicate the picture. In a Toronto cohort of 285 children followed for a median of 6.1 years, Singh and colleagues found that 43.5% had abnormal neurological outcomes, and older age at stroke predicted worse outcomes on that broader neurological measure. Family background matters too. In a small Austrian study, socioeconomic status explained up to 42% of the variance in cognitive outcome after childhood stroke, more than any clinical factor. For a child who has had a stroke, a neuropsychological assessment arranged through the paediatric neurology team can guide school support.

There is no standard figure. The loss depends on the size and location of the damage, and a stroke can severely impair one ability, such as language, while leaving others close to their earlier level.

Yes, but the results need careful interpretation. Aphasia, neglect and weakness can lower specific subtest scores for reasons other than reasoning, so a neuropsychologist chooses tests that work around these problems.

No. About half of stroke survivors show measurable cognitive impairment in hospital-based studies, which means many others do not.

Some people do improve. In one study of patients followed from 3 to 24 months after a stroke, 7.8% improved, 78.2% were stable and 14% declined.

Left-hemisphere damage more often lowers verbal scores, and right-hemisphere damage, especially in the parietal lobe, more often lowers visual and spatial scores.

Stroke IQ loss is real for many people, but it rarely takes the form of a uniform drop. Hospital studies find cognitive impairment in about half of survivors, with the pattern set by where the stroke struck: language after many left-hemisphere strokes, visual and spatial skills after many right-hemisphere strokes. Brief screens such as the MoCA catch more than the MMSE, and a neuropsychologist can separate a specific loss from general reasoning ability. Anyone worried about thinking after a stroke should raise it with their stroke team or neurologist and ask about a neuropsychological assessment. For adults without a neurological condition who want a benchmark of their reasoning, take a full-length online IQ test.

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2. Lo, J. W., Crawford, J. D., Desmond, D. W., Godefroy, O., Jokinen, H., Mahinrad, S., ... Sachdev, P. S. (2019). Profile of and risk factors for poststroke cognitive impairment in diverse ethnoregional groups. Neurology, 93(24), e2257-e2271. doi.org

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12. Singh, J., Slim, M., Moharir, M., Westmacott, R., Krishnan, P., MacGregor, D., ... deVeber, G. (2024). Long-term neurologic outcomes in pediatric arterial ischemic stroke: The impact of age and lesion location. Stroke, 55(11), 2622-2631. doi.org

13. Bartha-Doering, L., Gleiss, A., Knaus, S., Schmook, M. T., & Seidl, R. (2021). Influence of socioeconomic status on cognitive outcome after childhood arterial ischemic stroke. Developmental Medicine & Child Neurology, 63(4), 465-471. doi.org

Hero image: Chicago Ambulance at Night 6D2B5162, by Tony Webster, licensed CC BY 3.0 (creativecommons.org/licenses/by/3.0). Via Wikimedia Commons.