Two recently published studies are showing evidence that electrical stimulation to a specific area of the brain can significantly enhance memory and learning. Despite there being limited real-world applications to this kind of invasive electrical brain stimulation, the research suggests a possible future where implantable neural stimulation systems could help improve a person's memory.

A great deal of research is currently underway examining methods of stimulating our brains to do everything from treat depression to play games. Some of this research utilizes a non-invasive method of brain stimulation called Transcranial Magnetic Stimulation (TMS), where a magnetic pulse is used to induce electrical activity in a targeted region of the brain. While this method is obviously more practically applicable and easy to study, it is also limited in the specific areas of the brain it can target.

Deep Brain Stimulation (DBS), on the other hand, involves precisely firing electrical pulses into select regions of the brain via implanted electrodes. For over twenty years DBS has been used as a treatment for Parkinson's disease, and more recently epilepsy. As it isn't especially practical to implant electrodes into a person's brain just for the sake of an experiment, most DBA research utilizes patients who already have implanted electrodes for clinical treatment reasons.

Two newly published studies involving subjects with electrodes already implanted for epilepsy treatment, have investigated ways that electrical currents can improve memory and learning. Both studies have focused on the lateral temporal cortex region of the brain as a key area for memory enhancement.

The first study, led by researchers at the Mayo Clinic, examined 22 subjects directed to read a list of words while electrical simulation was applied to one of four different areas in the brain. The subjects were then directed to recall the words previously spoken to see if their verbal short-term memory was affected by the electrical stimulation.

The four subjects receiving stimulation to the lateral temporal cortex recalled significantly more words than the other subjects receiving stimulation to different brain regions. Despite the very limited scope of the study the researchers suggest these findings point to the lateral temporal cortex as being a key target for future memory stimulation work.

The second study, from the University of Pennsylvania, examined electrical stimulation in a similar brain region but focused on whether the timing of the electrical pulses affected the memory outcomes. Prior studies by the team had revealed that electrical pulses could negatively affect memory retention if delivered at the wrong time.

The team started by building a computer model that could examine the brain activity of each participant while they engaged in several free-recall memory tests. This model could then identify the differences in brain activity between when something was learned effectively or ineffectively. Each participant subsequently took part in a session involving electrical brain stimulation that was triggered when the computer model identified in real time whether a word being viewed was not effectively learned. The results showed that the precise timing could enhance learning and memory by up to 15 percent.

"By developing patient-specific, personalized, machine-learning models we could program our stimulator to deliver pulses only when memory was predicted to fail, giving this technology the best chance of restoring memory function," explains Michael Kahana, one of the lead investigators on the project.

So as well as now knowing where to specifically target deep brain electrical stimulation to enhance memory, the Penn study shows that precisely timing the pulses is also key to a successful result. The long-term outcomes from these various studies excitingly foreshadow a future where implantable neural stimulation systems could be used to help those with traumatic brain injuries or neurodegenerative diseases that result in major memory problems.

But not everyone is convinced this kind of research is anything more than a compelling academic experiment. Several Alzheimer's and dementia researchers suggest these results offer no indication as to whether this method would be effective in patients with actual damage to memory centers in the brain.

"The results, while exciting, do not at this stage have therapeutic implications and would need to be replicated in clinical populations such as Alzheimer's disease," says Roi Cohen Kadosh from the University of Oxford.

The US government is perhaps less skeptical about the perceived outcomes with both the University of Pennsylvania and Mayo Clinic research being funded, either in part or completely, by a program called Restoring Active Memory from the Defense Advanced Research Project Agency (DARPA).

The Mayo Clinic study was published in the journal Brain.

The University of Pennsylvania study was published in the journal Nature Communications.