Small, 64, was in Hong Kong last month to advise on brain health enhancement as part of an Asia-Pacific Wellness Tour with global nutrition company Herbalife. Coinciding with Small's visit, Herbalife released findings of the survey, conducted by market research company Lightspeed GMI.

Four hundred Hongkongers between the ages of 25 and 45 who work full time were polled online on their use of digital devices and lifestyle habits in September.

"What's interesting is the survey for first time shows this connection between overuse or higher use of digital devices and more complaints of memory disturbances in Hongkongers," says Small, a professor of psychiatry and bio-behavioural sciences, and a member of the nutrition advisory board of Los Angeles-based Herbalife.

Nearly two out of three respondents agreed with the statement: "Overuse of digital devices is detrimental to one's memory and intelligence." Overall, 63 per cent reported experiencing memory loss in their daily lives and 48 per cent reported experiencing memory loss at the workplace.

Respondents who spent more than six hours daily on their digital devices were more likely to report experiencing forgetfulness in the past month compared to those who spent fewer hours - 70 per cent compared with 57 per cent. Further, the incidence of reported memory loss was slightly greater in the under-35s (70 per cent) compared to the older respondents (65 per cent).

Almost all respondents (95 per cent) owned at least two digital devices, and 43 per cent spent at least eight hours on these devices a day. One in 10 of the under-35s reported spending more than 14 hours daily on their devices.

In his 2008 book , Small talks about "digital natives", young people who have grown up with always-on technology and whose brains have become hardwired to use it, and "digital immigrants", the older generation who grew up at a time with less technology and are slightly more reluctant to embrace it.

"The big difference between those two groups, we found, is even though the younger people are spending a lot of time getting good at those technological skills, they're neglecting a lot of other skills and not spending time developing other mental skills," says Small. "The ability to have face-to-face conversations, maintain eye contact, recognise emotional expression in the face, or pick up on non-verbal cues during a conversation - those skills are waning."

The survey also found poor dietary and exercise habits among the respondents: less than 15 per cent met the government's recommended intake of fruit and vegetables, and only 15 per cent met the exercise recommendations of at least 30 minutes three times a week. Forty per cent said they did not exercise at all.

Small says this unhealthy behaviour compounds digital dementia. He cites US research that shows people who don't eat enough fruit and vegetables, don't exercise enough, and/or smoke have more memory complaints.

The term digital dementia was coined a few years ago in South Korea, after doctors reported seeing young patients with memory and cognitive problems, conditions that were more commonly linked to brain injuries.

According to Yoon Se-chang, a psychiatry professor and doctor at Samsung Medical Centre in Seoul, South Korea: "As people are more dependent on digital devices for searching information than memorising, the brain function for searching improves whereas an ability to remember decreases."

Dr Manfred Spitzer, a German neuroscientist and author of the 2012 book , warns that children who spend too much time on electronic devices could experience irreversible deficits in brain development.

Spitzer writes: "In 2020 the brains of multitasking teens and young adults will be networked differently than the brains of people older than 35 years, and this will result in bad and sad consequences. They will hardly be able to remember anything; most of the energy will be spent on exchanging short social messages or on entertainment and diversion from a really deep commitment to the people and to knowledge."

Some scientists, however, have rubbished the concept of digital dementia. Michael Madeja, professor of neurosciences at the University of Frankfurt, says the term is mainly for "advertising appeal" and that there's no evidence that using digital media leads to harmful changes in the brain, and particularly not those found in types of dementia such as Alzheimer's disease.

According to Madeja, the impact of digital devices on cognitive performance is subjective. "Whether a decrease in memory function is undesirable, or tolerated, or even desirable because it frees up some of the brain's processing capacity for other tasks is something that is decided by our society and the environment," he says in an interview on Alumniportal Deutschland.

Small takes a similar balanced approach. "The devices are not all bad," he says. "It's really about content, context and dose."

In fact, Small's previous research involving a group of internet-naive elderly who learned how to search the net showed that using digital devices can help exercise our neural circuits and brain cells.

"If you're playing the same violent video game for 14 hours a day, that's not going to be good. Other studies show excessive screen time is associated with worse symptoms of attention deficit and, in children, worse performance at school," says Small.

"What we want is to balance the online time with offline time. You can even use your devices to remind you it's time to take a break, to have a conversation, to have healthy meal or snack, to exercise or meditate. Use your device in a way that it enhances your life."

How much digital time is too much? Small says not enough studies have been done to know for sure. For now, it simply depends on the individual.

"I think we ought to ask ourselves, is this too much? Am I getting mental fatigue? Am I not getting enough exercise? Some people are more sensitive to it than others."

By making a conscious effort, digital dementia can be reversed, Small says.

One of his studies released this year involved 13-year-olds who were using their devices about four hours a day on average. The teens were sent to a five-day nature camp, during which they couldn't access their devices. Their emotional and social intelligence were tested before and after the camp, and Small says the teens' test performance "increased significantly" after just five days compared to a control group who continued using their devices.