Neuronal activity in human hippocampus predicts future memory formation

June 1, 2020

What happens in the hippocampus even before people attempt to form memories impacts whether they remember.

A new study analyzed neuronal recordings from the brains of epilepsy patients while they committed a series of words to memory. When the firing rates of hippocampal neurons were already high before the patients saw a word, they were more successful in encoding that word and remembering it later. But when hippocampal neurons were not already spiking very much, novel information was more likely to be poorly encoded and later forgotten.  A recent study has found that when neurons in the human hippocampus are already firing at high rates, people are more likely to remember. This finding suggests that the hippocampus has a “ready-to-encode” mode for memory formation. The hippocampus is thought to encode information into memories, in coordination with brain areas that process different types of information. The image shows the hippocampus encoding visual information (green dots) from the occipital cortex, spatial information (purple dots) from the parietal cortex, and sound (orange dots) from the auditory cortex. Download Full Image

The findings suggest that the gumball-sized hippocampus might have a “ready-to-encode” mode that facilitates remembering. The study was published in the June 1 issue of the Proceedings of the National Academy of Sciences. 

The study was a collaboration between the University of California, San Diego; Arizona State University; Barrow Neurological Institute; New Mexico State University; Veterans Affairs Medical Center in San Diego and the Neurtex Brain Research Institute. 

“We think new memories are created by sparse collections of active neurons, and these neurons get bundled together into a memory. This work suggests that when a lot of neurons are already firing at high levels, the neuronal selection process during memory formation works better,” said Stephen Goldinger, professor of psychology at Arizona State University.

Neuronal recordings from the hippocampus, amygdala, anterior cingulate and prefrontal cortex were collected from 34 epilepsy patients while they underwent clinical monitoring at Barrow Neurological Institute. During the experiments, the patients either saw or listened to a steady stream of words and had to indicate whether each word was novel or a repeat. At first, all the words were novel, but after a while most words repeated. 

The researchers calculated the average number of times a neuron fired in response to every word the study participants saw or heard. They also calculated the neuronal firing rates immediately preceding each word. Only the average firing rate in the hippocampus approximately one second before seeing or hearing a word for the first time was important: That neuronal activity predicted whether the participants remembered or forgot the word when it was repeated later on.

“If a person’s hippocampal neurons were already firing above baseline when they saw or heard a word, their brain was more likely to successfully remember that word later,” Goldinger said.

The neuronal activity measured in the amygdala, anterior cingulate and prefrontal cortex did not predict task performance. 

“A key question going forward is how to put our brains into ‘encoding mode’ when we wish to do so,” said John Wixted, professor of psychology at the University of California, San Diego, and one of the lead authors on the paper. “‘Encoding mode’ is more than simply paying attention to the task at hand. It is paying attention to encoding, which selectively ramps up activity in the part of the brain that is the most important for making new memories: the hippocampus. Since we know, based on earlier research, that people can actively suppress memory formation, it might be possible for people to get their hippocampus ready to encode as well. But how one might go about doing that, we just don’t know yet.”  

ASU alumna Megan Papesh, who recently moved to New Mexico State University, contributed to the work. 

Zhisen Urgolites from UC San Diego was first author on the paper, and Peter Steinmetz of the Neurtex Brain Research Institute, was senior author. David Treiman of Barrow Neurological Institute and Larry Squire of the Veterans Affairs Medical Center in San Diego and UC San Diego also contributed to the work.

The study was funded by the Neurtex Brain Research Institute, National Institute of Child Health and Human Development, National Institute of Neurological and Communicative Disorders and Stroke, National Institute of Mental Health, and Medical Research Service of the Department of Veterans Affairs.

Science writer, Psychology Department


5 digital resources for K-12 students and parents to check out this summer

June 1, 2020

For many years, Arizona families have looked to Arizona State University for a wide array of school year and summer programming, resources, education and inspiration to promote access to higher education for K-12 students. 

Access ASU program offerings include in-school presentations, camps and family engagement opportunities — connecting students and families with information and insight regarding financial aid, grants and scholarships, how to pick a major, resources for first-generation students and much more. A child's hands on a computer Download Full Image

As more students and families continue to socially distance, that work is not only continuing, it is in fact becoming even more accessible than ever online. ASU Director of Educational Outreach and Partnerships Marcelino Quiñonez said that delivering these resources to Arizona families is still crucial. Access ASU teams have pivoted to bring online even more resources that foster a college-going culture in Arizona communities and offer the services and support that help show how higher education can be attainable financially, academically and culturally for all students.

“We’ve always been dedicated to preparing Arizona students for success in college so they can thrive,” Quiñonez said. “We know we can’t slow down even though we’re at home. We will continue to connect with students and families so they have everything they need to know that higher education is attainable for them.”

Families can kick off their summers of college preparedness with these great digital resources thanks to Access ASU.

1. Sparky’s Spotlight

The new Sparky’s Spotlight YouTube series, for which Quiñonez acts as host, features some Spanish and some English episodes that cover frequently asked questions about the Free Application for Federal Student Aid, the first step in receiving grants and other financial aid. The series also features conversations with local community members and ASU sources about how to be successful in the transition to college and what higher education means to them.

2. Virtual workshops

When schools are open, Access ASU works with educators and counselors to bring information right to students in their schools. While families are at home, you can take advantage of these resources through a YouTube playlist. Topics include effective note-taking tips, stress management, choosing a major, transitioning from middle school, college readiness 101 and more. 

3. Sparky’s Virtual Experience

Students who want to participate in college readiness workshops, virtual college tours, SPARKS panels and career exploration do not need to wait. Sparky’s Virtual Experience features live sessions with ASU staff and faculty to those interested in learning more about what ASU has to offer. Students in eighth, ninth and 10th grade are eligible to participate. Workshops will be held on Monday, Wednesday and Friday for three hours each day. 

4. Summer programs 

The programs that ASU offers every summer to Valley students are online this year. Barrett Summer Scholars and César E. Chávez Leadership Institute participants will have access to college-level coursework, high-energy leadership and engagement in a virtual format. 

5. American Dream Academy Online

ASU’s eight-week program that gives families the tools and confidence to have successful academic careers and prepare for college is now online through Google Classroom. The curriculum is available in both Spanish and English. Find out why parents love this program, which shows how education can be attainable for every family. 

To access American Dream Academy Online, visit the Google Classroom. Join the class as a student using the “plus sign” icon in the upper right corner and enter the corresponding class code: jajpk2r for English and h6hmoyo for Spanish.

Hannah Moulton Belec

Digital marketing manager, Educational Outreach and Student Services