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  • Alzheimer’s disease is an irreversible, progressive brain disorder that slowly destroys memory and thinking skills and eventually even the ability to carry out the simplest tasks.

    In this online citizen science (OCS) project, citizens help scientists by analysing video clips of blood flowing through the brains of research mice to identify blockages – ‘stalls’.

    Rights: Human Computation Institute, CC BY-SA 4.0

    Stall Catchers

    Identifying whether blood can flow easily through vessels in the brain or whether there is a stall (blockage) is assisting scientists to research the connection between brain blood flow, Alzheimer’s disease and potential cures.


    Reach: Worldwide

    Nature of science focus: OCS projects can be used to develop any of the Nature of Science (NoS) substrands. Identify aspects of NoS that your students need to get better at or understand more fully and then frame your unit to be very clear about these things when you do them.

    Science capability focus: Gather and interpret data, Interpret representations

    Science focus: human biology, disease, medical research

    Some suggested science concepts:

    • Blood flows through a network of connected tubes (veins, arteries, capillaries) that link together the major organs of the body (called the circulation system).
    • Blood is made up of red cells, white cells, plasma and platelets – all of which have specialist jobs to perform.
    • Blockages (obstructions) in the circulation system can occur for a variety of reasons.

    Many concepts could be learned – focusing on a few can often be more powerful. Develop your learning outcomes and success criteria from these concepts as well as the Nature of Science strand and the science capabilities.

    Some examples of learning outcomes:

    Students can:

    • explain why our circulatory system (including arteries, veins, capillaries and blood) is essential for our survival
    • identify features and functions of the human circulatory system
    • describe the effect of obstructed blood flow
    • explain why the reliability of results is important and how scientists know that citizens’ help in analysis is reliable
    • describe the meaning of a variety of scientific representations.
    Rights: Cornell University and Human Computation Institute, CC BY-SA 4.0

    Blood vessels in a mouse brain

    In Stall Catchers, you look at ‘movies’ of blood vessels that have been acquired from using a fluorescence microscopic imaging technique at Cornell University. In each movie, you analyse a single blood vessel highlighted in an orange outline to determine if the blood flow has stalled.

    About Stall Catchers

    A stall is when there is a blockage to blood flowing. Stalls reduce blood flow, and reduced blood flow in the brain has been linked to Alzheimer’s disease. By tagging the occurrence of stalls in videos of blood flow through mice brains, scientists are making real progress towards finding effective treatments in clearing stalls and restoring memory function.

    In this project, the citizen watches a focused area of video as it plays through layers of vessels in the brain. Does the blood flow continuously, or is there a blockage on the way? The citizen simply tags flowing or stalled. There is a very easy to understand tutorial and a substantial amount of support by way of information, videos and graphics. This project could be used in upper primary school to teach within a real science context, or it could be extended to be used in senior biology.

    Rights: Human Computation Institute, CC BY-SA 4.0

    Playing the game

    A user playing Stall Catchers on a tablet.

    This OCS project page has been written from a circulation and blood point of view but could equally well be approached with a brain function and health focus if that were appropriate.

    An interesting strength of this project is how open they are about discussing concerns over the accuracy of citizen science contributions and acknowledging how much citizens have given to their research. From a teaching perspective, this offers great opportunities for teachers to develop students’ understanding about the Nature of Science substrand ‘Understanding science supported by the science capability ‘Gather and interpret data’. How do we know we can believe the accuracy of these entries? What is reliable data? There are several video clips and graphics on the site that discuss this.

    The site has useful accessible explanations of the science involved in this research. Also, in the How To, For Educators tab there are a variety of short videos introducing the project, explaining the science behind their research, an interview with the lead scientist and some downloadable infographics.

    We feel an ethical obligation to extract as much value as possible from every minute that a person spends playing Stall Catchers.

    Stall Catchers

    It is possible to create a team so that you can monitor the contributions of all your students and compare your activity to that of other teams. It is also possible to ‘talk’ to the scientists through the blog and forum. This accessibility to the experts has been shown to be a powerful connection and motivator with students and the subject material they are covering.

    The project also has a gaming aspect. Participants who catch stalls build up their score, level up and compete in the game leaderboard.

    Nature of science

    Using this OCS project allows valuable conversations with students about their developing understanding of how scientists work and how scientists ensure rigour and reliable results from their investigations. There is also scope for developing students’ experience in interpreting a variety of representations.

    Related content

    Here are some planning tips for when you intend to use a citizen science project with your students.

    The Labelling the heart activity includes the interactive Label the heart and video Blood flow through the heart.

    Learn more about the brain with these resources:

    Useful links

    These resources are useful for learning about the circulatory system:

    These resources are useful for learning about Alzheimer’s disease:


    This outline was written as part of Victoria University of Wellington’s Citizen Scientists in the Classroom project funded by the Ministry of Education’s Teaching & Learning Research Initiative.

      Published 16 May 2019 Referencing Hub articles
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