Memory Is Not Infallible

by Guy McKhann, M.D.

August 28, 2013

In this issue, I would like to continue the discussion of mechanisms of memory. In the last issue I talked about a famous patient, H.M., who had surgery for epilepsy in 1954. In the surgery, the medial temporal lobe structures were removed on both sides. Post surgery, H.M. had improved in terms of his seizures, but had a unique memory defect: an inability to take in and retain new information. Researchers realized that memory was not dispersed throughout the cerebral cortex, but specific memory mechanisms were localized to sites of the brain, in this case the hippocampus and entorhinal cortex.

In this issue, we turn from memory in large structures to memory at a cellular level. An MIT News article describes two studies from the laboratory of Susumu Tonegawa. In these studies, performed on mice, cells in the hippocampus were activated while an electric shock was administered. To do this, the researchers used the methodology of optogenetics, in which light-sensitive channels are introduced into neurons. These channels can then be controlled by a specific gene, in this case a gene activated by memory processes. (The Guardian covers these studies as well and has quotes from outside researchers.)

The first paper describes their technique, showing the basic methodology to activate hippocampal neurons involved in memory. The second uses this technique to elucidate how a false memory might be created.

These studies of how memory can be manipulated cannot be directly applied to the human—yet. However, starting in the 1940s, the neurosurgeon Wilder Penfield noted that during the surgeries he performed to treat epilepsy, stimulation of specific sites in the temporal lobe would cause recreation of memories. So researchers know where to start. What is required is to adapt the techniques of optogenetics to the human brain—which will inevitably occur. The potentials for altering memory, erasing memory, and augmenting memory are all there.

Sources for Brain in the News

Our basic source for Brain in the News stories, the print media, is gradually dying. Further, as budgets are cut, science writers are being let go. The remaining science writers, in short supply, are asked to do a lot, covering health policy (e.g. Obamacare), large scale problems such as food toxicity issues, all the way to describing research results from individual studies.

In the meantime, science is booming, and is being presented to the public in new ways. For example, journals that present findings relating to the brain are now available in three forms: (1) the traditional hard copy appearing at given intervals (weekly or monthly); (2) a version of an accepted article on the web, weeks before the paper version; and in some cases (3) a web version of the entire journal, sometimes appearing as a separate journal from the print version, with its own editorial board. Other sources of input that we are using increasingly, particularly University-based publications, may report findings from an individual research group, or reviews of larger topics. These are often very informative, but not always read by the general public.

Keeping track of all this, for the preparation of Brain in the News, is an increasing challenge. Please feel free to contact Brain in the News editor Andrew Kahn ( or myself ( with publications or reports that we might not have otherwise considered.