A new predictive tool has been developed by a team of researchers to help clinicians identify which stroke patients are most likely to experience long-term cognitive difficulties. The ‘Cognition Calculator’, introduced in a study published in The Lancet: Healthy Longevity, uses information routinely recorded during hospital care to estimate the likelihood of problems with thinking, memory and communication six months after a stroke.

The study, conducted by researchers at the University of Oxford and the University of Birmingham, developed and tested a statistical model using clinical data collected from stroke patients during the early stages of hospital care. The model draws on data, including results from cognitive screening tests alongside information such as age and stroke severity. Researchers found that early cognitive performance was one of the strongest indicators of longer-term outcomes. 

Cognitive impairment is common following a stroke, but can be difficult to anticipate. Whilst post-stroke care has traditionally focused on physical recovery and preventing future strokes, researchers say thinking and communication difficulties are a major factor in patients’ long-term quality of life.

Professor Nele Demeyere, who led the research team, told Cherwell: “Many colleagues recognise the challenge of discussing cognitive outcomes with patients when there is so much uncertainty, so there is interest in tools that could help structure those conversations more clearly.”

Demeyere emphasised to Cherwell that the calculator is not yet intended to be used as a finished clinical product. Instead, she described the research as providing “rigorous groundwork” for future research to refine and test the model in wider clinical settings.

The research comes as the NHS is increasingly using digital tools and artificial intelligence to improve stroke care, including software now deployed across stroke centres in England to help clinicians analyse brain scans and make faster treatment decisions. Updated national stroke guidelines have also placed greater emphasis on early cognitive screening and long-term rehabilitation.

Dr Andrea Kusec, another Oxford researcher involved in the project, told Cherwell: “The response has been very positive, with many recognising the value of developing tools that can support conversations about what ‘life after stroke’ will be like.” 

She added: “Clinicians often are key in providing messages of hope and allay some of this uncertainty – this tool can become a way to support those tough conversations.”

The study also highlights the wide range of cognitive recovery after stroke. According to Kusec, one of the most surprising findings was how differently prediction models performed depending on the type of cognitive impairment involved, such as language, memory, or executive function. “This really speaks to the individual nature of post-stroke cognitive outcomes”, she said.

Researchers hope the model will now be tested in larger patient groups and across different healthcare settings. If validated further, it could help clinicians identify patients who may benefit from closer monitoring, targeted rehabilitation, or additional support.

Demeyere told Cherwell that the broader aim is to ensure cognitive health is recognised as a central part of stroke recovery. “Post-stroke care has historically focused, understandably, on survival and preventing recurrent strokes. Increasingly, we recognise that cognitive and communication difficulties are central to long-term quality of life… This study represents one step in that direction. It reflects a broader shift towards viewing cognitive health as a core component of stroke care.”

The findings are based on a major, cross-species analysis which revealed a shared pattern across many animals, from insects to mammals. Sperm that is stored (whether in males or females) deteriorates rapidly – resulting in reduced sperm performance, fertilisation success, and embryo quality. Crucially, the new study also offers insights into why this happens.

The researchers carried out a meta-analysis of 115 human studies (involving 54,889 men) and 56 studies across 30 non-human species. This confirmed that mature sperm in storage generally deteriorates in quality independently of the age of the male – a process called post-meiotic sperm senescence.

In humans, longer periods of sexual abstinence were associated with increased sperm DNA damage and oxidative stress, along with reduced sperm motility and viability.

Co-lead author Dr Rebecca Dean (Department of Biology, University of Oxford) said: ‘Because sperm are highly mobile and have minimal cytoplasm, they quickly exhaust their stored energy reserves and have limited capacity for repair. This makes storage particularly damaging compared to other types of cells. Our study highlights how regular ejaculation can provide a small but meaningful boost to male fertility.’

Differences between males and females

Sperm quickly exhaust their stored energy reserves and have limited capacity for repair. Our study highlights how regular ejaculation can provide a small but meaningful boost to male fertility.

Co-lead author Dr Rebecca Dean (Department of Biology)

Both male and female animals can store sperm as a reproductive strategy (in humans, sperm can last for several days in females but the effects of such storage are unknown). In males this ensures enough sperm are present for mating, and in females this can enable reproduction even when males are scarce. However, the study found a striking difference in the rate of sperm deterioration in males versus females. In the species studied, females are generally better than males at preserving sperm quality long-term.

‘This likely reflects the evolution of female-specific adaptations, such as specialised storage organs that provide antioxidants to extend sperm viability’, explained senior author Dr Irem Sepil (Department of Biology, University of Oxford). ‘These organs often secrete reproductive fluids to nourish sperm and could provide unexplored avenues for biomimicking technology to improve artificial sperm storage in the future.’

Lead author Dr Krish Sanghvi (Department of Biology, University of Oxford) added: ‘Ejaculates should be viewed as populations of individual sperm which undergo birth, death, ageing and selective mortality. The rates of these demographic processes can differ in males and females, mediating the “demographic” structure of sperm populations and sex-specific differences in sperm storage effects.’

Implications for human fertility

That sperm can age in both sexes independently of the organism’s age has been largely ignored in reproductive medicine. The findings therefore have immediate implications for clinical practice. For instance, the results suggest that the upper limit of seven days in the WHO guidelines may be too long. This aligns with recent evidence suggesting that ejaculating within 48 hours of providing a sample can significantly improve IVF outcomes.

By breaking down the barriers between biomedical and zoological research, this study provides a new lens for understanding reproduction. Besides influencing protocols in fertility clinics and assisted reproduction, the findings could also benefit captive breeding programmes for endangered species – as well as deepening our understanding of how species evolved mechanisms to reduce sperm damage during storage.

The study ‘Sperm storage causes sperm senescence in human and non-human animals’ has been published in Proceedings of the Royal Society B.