学进去

People’s ability to remember fades with age — but one day, researchers might be able to use a simple, drug-free method to buck this trend.

In a study published on 22 August in Nature Neuroscience, Robert Reinhart, a cognitive neuroscientist at Boston University in Massachusetts, and his colleagues demonstrate that zapping(刺激) the brains of adults aged over 65 with weak electrical currents repeatedly over several days led to memory improvements that persisted for up to a month.

Using a non-invasive method of stimulating the brain known as transcranial alternating current stimulation (TACS), which delivers electrical currents through electrodes on the surface of the scalp, Reinhart’s team conducted a series of experiments on 150 people aged between 65 and 88. Participants carried out a memory task in which they were asked to recall lists of 20 words that were read aloud by an experimenter. The participants underwent TACS for the entire duration of the task, which took 20 minutes.

After four continuous days of this protocol, participants who received high-frequency stimulation of the dorsolateral prefrontal cortex(背外侧前额叶皮质) had an improved ability to remember words from the beginning of the lists, a task that depends on long-term memory. Low-frequency zaps to the inferior parietal lobe(顶下小叶) enhanced participants’ recall of items later in the lists, which involves ‘working’ memory — the memory that allows the brain to store information temporarily. Participants’ memory performance improved over the four days — and the gains persisted even a month later. Those who had the lowest levels of general cognitive function before the study experienced the largest memory improvements.

“I was both impressed and surprised by this, by this paper,” says Simon Hanslmayr, a cognitive neuroscientist at the University of Glasgow, UK. He notes that along with other scientists, he has been sceptical about whether TACS can lead to meaningful changes in cognition. One issue has been that TACS devices generate electrical currents much weaker than those created by other methods of stimulating the brain, so it hasn’t always been clear whether they can transmit enough electricity to the brain to modify its function. However, the authors of this study convincingly showed that their protocol was linked to “consistent and quite strong improvements in memory”, Hanslmayr says.