Dr Tim Brennen of Tromso University in Norway investigated whether well-known seasonal mood swings, such as seasonal affective disorder, were accompanied by corresponding shifts in memory and attention.
He gave 100 people a variety of mental tasks and found they had quicker reaction times, better memory recall and were less likely to be confused during the winter.
His nimble-witted victims all lived in Tromso in northern Norway where the sun does not rise for two months in winter and in summer does not set for two months.
Dr Brennan, who presented his findings at the British Psychological Society's London conference this week, argued that the widespread belief that people get groggier and more forgetful in the winter is unfounded.
He said: "The very northerly latitude of this study provides optimal conditions for detecting any impairments of cognitive performance in winter.
"The data gives no grounds for concluding that cognitive performance in winter is worse in summer."