Deep Brain Electrical Stimulation Shown to Improve Memory

UCLA neuroscientists have demonstrated that they can strengthen memory in human patients by stimulating the entorhinal cortex in the brain. The finding could lead to a new method for boosting memory in patients with early Alzheimer’s disease.

Considered the doorway to the hippocampus, which helps form and store memories, the entorhinal cortex plays a crucial role in transforming daily experience into lasting memories.

Dr. Itzhak Fried, a professor of neurosurgery at the David Geffen School of Medicine at UCLA, and colleagues followed seven epilepsy patients who already had electrodes implanted in their brains to pinpoint the origin of their seizures. The researchers implanted intracranial depth electrodes in seven subjects to identify seizure-onset zones for subsequent epilepsy surgery. The subjects completed a spatial learning task during which they learned destinations within virtual environments. During half the learning trials, focal electrical stimulation was given below the threshold that elicits an afterdischarge (i.e., a neuronal discharge that occurs after termination of the stimulus).

Using a video game, the researchers tested whether deep-brain stimulation of the entorhinal cortex or the hippocampus altered recall. Patients played the role of cab drivers who picked up passengers and traveled across town to deliver them to one of six requested shops.

“When we stimulated the nerve fibers in the patients’ entorhinal cortex during learning, they later recognized landmarks and navigated the routes more quickly,” Fried said. “They even learned to take shortcuts, reflecting improved spatial memory.

The use of stimulation only during the learning phase suggests that patients need not undergo continuous stimulation to boost their memory, but only when they are trying to learn important information, Fried noted. This may lead the way to neuroprosthetic devices that can switch on during specific stages of information processing or daily tasks.

“Our preliminary results provide evidence supporting a possible mechanism for enhancing memory, particularly as people age or suffer from early dementia,” Fried said. “Future studies will determine whether deep-brain stimulation can enhance other types of recall, such as verbal and autobiographical memories. No adverse effects of the stimulation were reported by the seven patients.”

What about non-intercranial stimulation?

Last week a team of ethicists from Oxford released a paper on the implications of using Transcranial Direct Current Stimulation (TDCS) to improve cognition in human beings.  Recent years have seen some encouraging, if preliminary, lab results involving TDCS, a deep brain stimulation technique that uses electrodes placed outside the head to direct tiny painless currents across the brain. The currents are thought to increase neuroplasticity, making it easier for neurons to fire and form the connections that enable learning. There are signs that the technology could improve language acumen, math ability, and even memory.

Roi Cohen Kadosh, a cognitive neuroscience scientist at Oxford University’s Department of Experimental Psychology, and a team of researchers have studied about 120 volunteers, looking at their performance in mathematics both before and after what is known as Transcranial Direct Current Stimulation.

The volunteers were divided up into two groups — some were given the stimulation and others were given a kind of placebo stimulation. In his research Cohen Kadosh has found that those who were given the electrical stimulation and received cognitive training in mathematics improved their ability to do it.

In a report in Current Biology, Cohen Kadosh and his co-authors write: “TDCS studies have shown that it is possible to enhance fundamental human capacities, such as motor and sensorimotor skills, vision, decision making and problem solving, mathematical cognition, language, memory, and attention — improvements that seem to persist without apparent cognitive side effects.”

The Oxford paper argues that TDCS has now reached a critical stage where its risks must be carefully considered before the research goes further.