According to research published in 2015 by the journal Functional Foods in Health and Disease, and later in 2016, Kristin Nieman PhD have found that Spearmint Extract administered daily for 90 days made 300 % improvement in the quality of their working memory compared with placebo recipients.
The spearmint supplementation translates to improved alertness for the 90 subjects who participated in the study.
In a separate spatial working memory cognitive function test (the ability to know where items are arranged in space, and how to use this information), the participants also made nearly 300% improvement. Note that this result is achieved using standardised spearmint extract (900mg, standardised to 14.5% Rosmarinic acid) So you are probably unlikely to achieve the same result by just drinking commercial spearmint tea.
If you are looking to boost your brain using Spearmint extract, make sure you get access to top quality high rosmarinic acid tea or extract.