Professor Koga tested another group who had a normal breakfast.
He found that the ice cream group were better at processing new information and showed faster reaction times.
READ MORE: • Chocolate cake is the next big breakfast trend
After examining the subjects' brain activity, Professor Koga found that ice cream eaters fired off an abundance of high-frequency Alpha-waves.
These waves are linked with reduced mental irritation and high alertness.
Professor Koga considered that the ice cream eaters may have simply been shocked into high alert by the ice cream's freezing temperature.
He tested another group, this time giving them a cold glass of water as soon as they woke up.
While the cold water test subjects did show a boosted alertness and mental capacity, their levels did not reach the highs of those starting the day with ice cream.
Professor Koga is a specialist in psychophysiology who has previously investigated the links between certain food types and stress relief.
He has also examined how some food types affect the ageing process.
Professor Koga will continue his work with ice cream by trying to narrow down the precise ingredient giving his subjects a morning boost.
His study is not the first to sing the praises of a sweeter breakfast.
Scientists from Tel Aviv University conducted a study in 2012 which found that eating chocolate cake for breakfast could help in weight loss.
The researchers claimed that eating desserts along with the traditional proteins and carbohydrates found in a fry up helps stem sweet cravings later in the day.
The researchers even suggested that eating chocolate cake for breakfast left test subjects more satisfied with their meal, meaning they were more likely to keep the weight off.
But those looking to begin a breakfast diet of ice or cake should tread carefully.
Speaking on the Tel Aviv study, registered dietrician Katherine Tallmadge told Live Science: "I would never, in a million years, recommend cookies or cake for breakfast."
Experts generally agree that a large, balanced breakfast is the most healthy way to start the day.
"The last thing you want to do is get to an evening meal, and be starving," nutrition consultant and spokeswoman for the Academy of Nutrition and Dietetics Heather Mangieri told Live Science.
"That's the time that so many people overeat."