By Thursday, 18 September 2025, 12:19 Pm Press Release: Science Media Centre

Copyright scoop

Young contact sports players’ brains can show signs of
damage years before symptoms of long-term brain disease
appear, a small US study finds.

Researchers found
that brain tissues from under-51-year-old sports players had
more inflammation, loss of nerve cells, and damage to blood
vessels, than those of non-athletes.

suggests that repeated head knocks can cause long-term brain
damage regardless of whether the athlete goes on to develop
the degenerative brain condition Chronic
Traumatic Encephalopathy (CTE).

The Science Media
Centre asked experts to comment.

Associate Professor
Mangor Pedersen, Department of Psychology and Neuroscience,
AUT, comments:

“This study is a major step forward
in understanding how head impacts affect the brain. It shows
that damage can begin long before conditions like CTE are
diagnosed. We still need more research to understand who is
most at risk and when the brain becomes vulnerable. But
these findings are also consistent with what we are seeing
in our own MRI research, led by PhD projects from Dr Christi
Essex and Mayan Bedggood—that signs of brain
changes, including iron
accumulation and inflammation,
can appear just
weeks after a head injury in young

“Together, this has important implications
for sports safety and beyond. It highlights the need for
better monitoring, earlier detection, and stronger
protections to reduce the risk of long-term brain

No conflicts of

Dr Helen Murray, Head of the
Brain Injury & Neurodegeneration Research Lab at the
University of Auckland, comments:

study used a powerful tool called single-nucleus RNA
sequencing to examine how human brain cells respond to
repetitive head impacts. The study authors examined brain
cells from postmortem tissue from younger men (aged between
25 and 51) who had played contact sports, comparing three
groups: eight healthy controls with little or no history of
contact sports, nine athletes with a history of repetitive
head impacts but no chronic traumatic encephalopathy (CTE),
and eleven athletes who had been diagnosed with early-stage
CTE after death.

“Although a small number of
subjects were examined as is common for brain donation
studies, the research provides valuable insight into the
brain’s response to repeated head impacts. The study
focuses on the frontal cortex, which is an area often
affected early in CTE, but did not look directly at the
hallmark CTE lesions that are defined by patchy tau
pathology around blood vessels. Therefore, the findings
provide an insight into the broader brain changes linked to
years of head impact exposure.

“The study shows that
the repetitive head impact and CTE brains had fewer neurons
within a specific cortical layer deep in the folds of the
brain. This is the area most affected by shear stress during
a head knock and the area where CTE lesions specifically
develop. Importantly, the reduction in neuron number did not
correlate with the amount of tau pathology in that region,
suggesting that these changes happen early, before the
established markers of CTE pathology appear. However, the
data also shows that the number of neurons varied a lot
between individuals, and it is not yet clear what
these changes mean for brain function.

study also pointed to inflammation as an early and lasting
effect of repeated head impacts. Microglia, the brain’s
immune cells, show a shift from a healthy resting state to a
more inflamed, active state with increasing years of play.
Blood vessel cells and support cells called astrocytes also
showed signs of stress and activation. Together,
these changes suggest that repetitive head impact alone,
even without CTE pathology, is linked to processes of
inflammation, blood vessel disruption, and neuron
loss. This work supports the findings from our lab group at
the University of Auckland Centre for Brain Research,
published earlier this year, showing that astrocyte-mediated
inflammation is a key feature of the CTE

“While more work is needed to understand
the functional consequences of these findings, this study
strengthens the evidence that years of repeated head impacts
can induce chronic changes in the brain’s inflammatory
cells, even in young athletes who might never develop CTE.
The findings of this study emphasise the importance of
developing strategies to reduce exposure to head impacts in
training and games and to be cautious in our approach to
head injury management and return to

Conflict of interest statement: “New
Zealand representative in ice hockey. Currently researching
the neuropathology of Chronic Traumatic Encephalopathy with
funding from the Health Research Council of NZ and the
Neurological Foundation of NZ.”

Patria Hume, Professor Human Performance, AUT,

“This research has suggested a new idea:
repeated head knocks may first cause other types of brain
damage and inflammation, which could be responsible for
early symptoms. The known CTE brain changes might only show
up later. This is a shift from previous thinking, which
focused on a specific brain protein (called p-tau) as the
main cause of the disease and its symptoms. The new study
opens the door to fresh ways of understanding and tackling

“One of the biggest challenges in CTE research
is that the symptoms people experience, like changes in
mood, memory, or behaviour, don’t always match up with the
amount of disease found in their brains after death. People
without the classic signs of CTE in their brains can have
symptoms that look just like those who do have it. The
authors of this new study openly admit that the symptoms
seen in the people examined weren’t fully explained by the
usual brain changes linked to CTE.

“However, the
study’s design means we can’t say for sure that head
impacts directly cause these changes, or that these changes
always lead to CTE. The study did not clearly explain how
head injury history was measured, and did not link its
findings to real-life symptoms. Without that connection,
it’s hard to know what the results mean for athletes or
the public. The findings are important, but more research is
needed to understand the full story.”

research relies on brain samples taken after death, making
it impossible to track how these changes develop over time.
Without following people during their lives, it’s hard to
know if these changes always lead to disease, or if they
might be part of a different process altogether. The
study’s conclusions may be overstated.

study offers new clues about how head injuries might affect
the brain, it doesn’t provide a way to diagnose or treat
CTE in living people. Until researchers can reliably
identify who has the disease during life, and link brain
changes to symptoms, promises of new treatments remain out
of reach. The study is a step forward, but it’s not the
final answer.”

Conflict of interest statement:
“As a sports injury biomechanics expert employed by AUT, I
have no conflicts to declare.”

Professor Gisela
Sole, School of Physiotherapy, University of Otago,

“This study found signs of damage and
inflammation in post-mortem brain tissue of relatively young
contact sports athletes (late twenties to fifty years old)
who had experienced repeated head impacts, concussions, and
in severe cases, CTE. These worrying findings highlight why
early diagnosis and treatment are critical for young people,
especially when dealing with second or third concussions
while the brain is still healing from the first

“Many players don’t report suspected
concussions, preferring to keep playing rather than being
sidelined for the minimum three-week recovery period. Rest
remains crucial after even mild concussions – at least 48
hours of reduced activity, followed by gradual return to
learning and sports based on symptoms like dizziness,
headaches, fatigue, balance problems, light or noise
sensitivity, or concentration difficulties.

these new findings, getting diagnosed by trained healthcare
providers (doctors, nurse practitioners, or
physiotherapists) is even more important for proper rest
guidance and graduated return to activities. The mandatory
stand-down period from sports is critical to allow brain
inflammation to settle and minimize long-term risks. Players
need medical clearance before returning to contact sports,
as healthcare providers can detect hidden symptoms not
apparent during daily activities.

“Developing brains
in children and adolescents are particularly vulnerable and
need adequate healing time. Poor concussion management can
lead to longer recovery, increased reinjury risk, and
lasting problems with memory, concentration, and academic
performance. Parents, teachers, and coaches have greater
responsibility to ensure players with suspected concussions
seek immediate medical assessment.

long-term disability for one game simply isn’t worth

Conflict of interest statement: “Professor
at the School of Physiotherapy, University of Otago;
completed Lottery Health funded research project to
co-design and implement a framework for management of
concussion in NZ secondary schools and a
website. Co-investigator on the World Rugby
funded ORCHID study, measuring head impacts via instrumented
mouthguards during rugby training/games in 2022/2023
(Principal investigator Prof Melanie

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