Stimulating the Memory System

Many research studies have attempted to stimulate human memory with implanted electrodes. The results remained mixed, with some experiments sharpening memory, while others muddled it. A recent study, however, showed that the timing of the stimulation is crucial. In a 2017 New York Times article, Benedict Carey describes a study conducted by the University of Pennsylvania’s research team, led by Michael Kahana and Youssef Ezzyat.  According to the study, well-timed pulses from electrodes implanted in the brain can enhance memory in some people. Importantly, the encoding of new information improves if the memory areas are "zapped" when they are functioning poorly. In contrast, when the areas are working well, the stimulations impair memory.

The participants were 150 people with severe epilepsy being evaluated for surgery. Through direct neural recording, the implanted electrodes monitored seizures, indicating whether one’s epilepsy is operable. Due to electrodes’ placement in or near memory areas, the participants were administered a series of memory tests. They memorized lists of words and had to recall them after a distraction. Meanwhile, the researchers monitored the participants’ brains for “hot spots” associated to memory encoding. The participants engaged in memorization tests as stimulations were delivered during low- or high-functioning brain states. The results showed that memory performance improved 12-13% when the stimulation arrived during a low or foggy state but decreased 15-20% when the stimulation was delivered in a good state.

These findings interestingly build upon previous memory research, including a study by Wang et al. (2014), in which Repetitive Transcranial Magnetic Stimulation (rTMS) was found to improve memory performance by increasing the connectivity between the hippocampus and other brain regions. Although the current study employed intracranial electroencephalography (EEG) while Wang et al. used rTMS, both studies stimulated the memory network during encoding and observed improved performance. This study’s finding about the significance of precise timing of stimulation importantly distinguishes it from past research and suggests a new direction to explore.

Because the participants were epilepsy patients in need of surgery and direct neural recording, the researchers were able to stimulate deeper in the brain than studies with healthy people allow. While being a strength of the study, this component also limits the generalizability of these findings. Further research is needed to determine whether this approach has potential in people with other conditions. Nevertheless, this pacemaker-like method might show promise in helping to reduce symptoms of dementia, head injuries, and other conditions. Stimulation during "foggy" states as opposed to high-functioning states is an intriguing finding, and the precise timing of stimulation may be a crucial area to explore further.

https://www.nytimes.com/2017/04/20/health/brain-memory-dementia-epilepsy-treatments.html