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Question

участники испытывали беспокойство в таких случаях: при мысли о решении задач, при виде учебника по математике, при нахождении рядом с кабинетом математики. 
All participants were qualmish in such situations as: when they thought about solve sums, when they saw the maths textbook, when they situated next to the maths room. 
пока участники выполняли разные тесты, ученые делали магнитно-резонансную томографию их мозга. 
participants were doing different tests when scientists made MRT of the brain.

Саша Хныкин · Accepted Answer

The participants felt nervous in such situations as: when they thought about solving problems, when they saw maths textbook, when they stayed next to the Maths room. 
While the participants were doing various tests, the scientists were performing MRT of their brains.

Алексей Бесшапошников · Answer

все нормальна

Максим Фирсов · Answer

во втором предложении поменять основную и зависимую части предложений местами.

Марго · Answer

1) После предлогов нужен герундий, а не глагол. Лексика. 
2) While participants were doing different tests the scientists were doing/carrying out the MRT of their brains