Researchers at the University of Toronto conducted an experiment to understand how periods of intense mental activity impact human productivity.

Over 12 weeks, they observed students performing short daily tasks designed to test clarity of thinking. Participants reported on their goals, achievements, mood, sleep quality, and workload.

The researchers aimed to find out why some days thinking feels sharp, while on others there is “brain fog” and decreased concentration. When students’ minds were sharp, they not only completed planned tasks more effectively but also set higher goals for themselves. During periods of reduced cognitive clarity, activity was limited to simple daily tasks, and larger projects had to be postponed.

Participants demonstrated better cognitive performance after good sleep and during the first half of the day, while activity decreased in the afternoon. Motivation and concentration were closely linked to mental sharpness, whereas stress impaired cognitive functions.

The researchers concluded that periods of “mental peak” are equivalent in effect to an additional 30–40 minutes of work per day.

Increased workload and concentration boosted productivity for one or two days, as people could mobilize to complete short-term tasks. However, prolonged overwork over a week had the opposite effect: concentration declined and achieving goals became more difficult. The study results were published in Science Advances.