Stimulation Gives Working Memory a Boost

Working memory is essential to everyday tasks. It helps us hold memories temporarily whilst being distracted. We use it as children, to retain information in lessons if (when) we get distracted by our friends, and as adults to remember where we parked the car whilst the kids are acting up. In later life, however, working memory declines and makes these tasks more difficult.

Now, a new study from Boston University researchers suggests that non-invasive stimulation using weak electrical current can reverse the effects of aging on working memory, at least temporarily, by synchronizing different rhythms of brainwave.

The findings, say authors, show that the superior working memory seen in the young can be “brought back” in age, and could prove invaluable as we face the reality of a globally aging population. Furthermore, poor working memory and functional connectivity problems are hallmarks of neurological disorders like Parkinson’s, schizophrenia, and autism, and non-invasive stimulation could prove invaluable for research into these disorders. “Our hope is that this work will lay basic science groundwork for an entirely new avenue of research where we develop non-invasive new neuroscience tools to help treat people who are suffering from brain disorders,” says study author Robert Reinhart.

The study involved 84 volunteers; half in their twenties and the other half aged between 60 and 76. The participants were asked to undertake a working memory task. During the task, the older subjects were given high-definition transcranial alternating-current stimulation (tACS), which allows targeted electrical stimulation to specific brain regions. The stimulation was customized to each individual’s brainwave oscillations to target what Reinhart calls the “sweet spot” frequency for each brain. The researchers used electroencephalogram (EEG) caps to measure the electrical signatures produced; the stimulating electrodes were built into the cap to enable simultaneous recording and stimulation. After 25 minutes of stimulation, (Reinhart says participants only feel “a tingling, itching and poking sensation” for the first 30 seconds), the older cohort’s working memory improved to the level of the younger group unstimulated memory. This improvement lasted the entire duration of the experiment, up to 50 minutes post-stimulation – its unknown how long the effects lasted after Reinhart stopped measuring.

Reinhart says that his team thinks the stimulation works by synchronizing brainwaves between two areas implicated in working memory function; the prefrontal cortex, thought to be the site of complex cognitive behavior in the brain, and the temporal cortex, on the left side of the brain. These two areas are thought to communicate with each other using low frequency brainwaves of about 8Hz, but Reinhart’s team showed that synchronization had broken down in their older participants’ brains but was improved by the tACS. Specifically, tACS boosted interactions between theta and gamma rhythms in the left temporal cortex, and increased synchronization of theta brainwaves between the left temporal cortex and prefrontal cortex.

Reinhart was keen to caution that the research remains a distance from the clinic but suggested that a refined and miniaturized version of the technology could someday become an adjunct therapy for brain disorders. Reinhart points out that disorders arise both due to over- and under-connectivity, and in followup experiments, tACS proved capable of temporarily de-synchronizing brainwaves in younger adults, as well as improving synchronization in the elderly, meaning that there could be clinical potential for all types of connectivity disorder if these results can be replicated in clinical trials. That replication is no small feat, however, as emphasized by UCL’s Prof Robert Howard, who was not involved in the study, “While this is an interesting and positive piece of research, suggesting that carefully positioned and timed electrical stimulation of the brain can potentially improve short-term memory function in older people, I would caution against any uncritical assumption that this will translate into clinical benefit. The findings need to be replicated under clinical trial conditions, with larger numbers of participants and with robust blinding of subjects and outcome assessors.”