During the past decade several new technological advances have enabled the identification of ensembles of neurons that encode a specific memory trace (engram cells) and for controlling the activity of engram cells so that recall or inhibition of a memory is controlled by the experimenter. The technologies include fluorescence 'tagging' of engram cells and optogenetic activation or inhibition of the engram cells. In this episode professor Tomás Ryan talks about these developments and his own research which provides evidence that memory recall involves competition between different engrams, that forgetting a memory is an active process in which recall of the memory is suppressed. Studies of amnesia have shown that memory engrams can still exist and can be recalled by electrical stimulation.

LINKS

Review and Perspective articles

https://www.cell.com/action/showPdf?pii=S0166-2236%2825%2900153-5

file:///Users/markmattson/Downloads/s41583-021-00548-3%20(1).pdf

Engram cell connectivity and memory

https://www.cell.com/action/showPdf?pii=S0960-9822%2823%2901512-9

Forgetting and engram expression

https://pmc.ncbi.nlm.nih.gov/articles/PMC11537488/pdf/elife-92860.pdf

Recent discoveries show that some neurodegenerative disorders occur because of abnormalities in the processing of RNA in the cell nucleus and/or its export from the nucleus. Johns Hopkins University Associate Professor Shuying Sun is at the forefront of research that is establishing the molecular mechanisms responsible for RNA dysregulation in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Her research is contributing to a rapid acceleration of understanding of the causes of ALS and FTD and to the development of new pharmacological and gene therapy-based treatments for these disorders.

LINKS

Dr. Sun's laboratory webpage:

https://sunlab.jhmi.edu/

Review article

https://pmc.ncbi.nlm.nih.gov/articles/PMC11790913/pdf/44318_2024_Article_352.pdf

Original research articles

https://pmc.ncbi.nlm.nih.gov/articles/PMC5754368/pdf/41467_2017_Article_2495.pdf

https://pmc.ncbi.nlm.nih.gov/articles/PMC6895427/pdf/nihms-1539444.pdf

https://www.biorxiv.org/content/10.1101/2025.09.30.679260v1

https://www.biorxiv.org/content/10.1101/2025.09.30.679260v1

https://www.biorxiv.org/content/10.1101/2025.06.13.659508v1

NOTE: This lecture with slides presented can be found on the Brain Ponderings YouTube Channel.

This episode begins by highlighting recent evidence showing adverse effects on the brain of excessive activation of the mTOR pathway as a consequence of dietary branched chain amino acid consumption. Then I describe evidence that Beyond the age of 40 years brain aging results in progressive decrements in function which are associated with reductions in gray matter and synapse numbers particularly in brain regions that play critical roles in memory, executive functions, and task switching. Recent progress has been made in identifying molecular markers of brain aging in samples of blood or cerebrospinal fluid heralding a better understanding of factors that accelerate or retard brain aging. This episode reviews some of the salient research in these areas.