The first evidence that low-current electrical stimulation, known as microstimulation, can enhance human memory has been published in the journal eLife.
The study, from the University of California, Los Angeles (UCLA), suggests that microstimulation – a departure from the more commonly used deep-brain stimulation techniques – is sufficient to modulate human behaviour, opening potential new avenues for treating patients with chronic memory impairment.
“A region in the brain called the hippocampus is crucial for learning and memory. The formation of memories is thought to be caused by hippocampal long-term potentiation (LTP), a persistent increase in synaptic strength following high-frequency stimulation,” explains senior author Dr. Itzhak Fried, Professor of Neurosurgery and Psychiatry at the David Geffen School of Medicine at UCLA.
“It has previously been shown in rodents that hippocampal LTP may be induced through electrical stimulation of the perforant path, a route that connects the entorhinal cortex to the hippocampus. We wanted to find out if similar techniques could be used to help improve memory in humans.”
To answer this question, Fried and his team recruited thirteen neurosurgical patients undergoing treatment for epilepsy to take part in a microstimulation study. The patients were implanted with tiny deep-brain electrodes to pinpoint the focus of their epilepsy, so that the area could be removed later for potential cure.
First, the participants completed a behavioural task in which they viewed novel portraits of people on a computer screen. During the task, the researchers delivered low-current electrical stimulation to the subjects’ brains via the microelectrodes, targeted to the left or right of the entorhinal area which works as a kind of ‘hub’ in the memory formation network.
The participants next performed a distractor task, before being presented with a series of images and asked to identify whether each one was ‘old’ (presented during the behavioural task) or ‘new’.
Analysing the results of the test, the scientists found that microstimulation of the right entorhinal area significantly improved performance in the person recognition task, while stimulation of the left entorhinal area had no effect. Microstimulation allowed the participants to both recognise the faces they had seen during the behavioural task and to reject ‘lures’ – images of people with similar faces. This is consistent with previous findings that the right hippocampus shows increased metabolic activity during the process of learning new faces.
“Our results pave the way for using microstimulation to interrogate the circuits involved in human memory in a more targeted way,” says co-lead author Emily Mankin, Postdoctoral Fellow at UCLA. “In the future, we will need to conduct studies to further examine an array of memory tasks and stimulation patterns. This will help us explore the potential of these methods to aid memory function in a variety of neurological disorders, such as dementia, which are prevalent among the aging population.”
This study was carried out by an interdisciplinary team of scientists and clinicians at UCLA, which also includes co-lead authors Ali Titiz and Michael Hill, and co-senior author Nanthia Suthana, Assistant Professor of Psychiatry and Neurosurgery.
For more information about the David Geffen School of Medicine at UCLA, as well as senior author Dr. Itzhak Fried, please visit: http://medschool.ucla.edu and https://www.uclahealth.org/itzhak-fried.
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