Zapping Memories Away

By Neuroskeptic | July 22, 2010 3:05 pm

Imagine you’re about to have to do something horrible or embarrasing, like say, admitting that you read Neuroskeptic. Wouldn’t it be nice to be able to switch off your memory for a while, so you at least didn’t have to remember it?

Well, now you can, as long as you have electrodes implanted in your brain. Lacruz et al, based at London’s Institute of Psychiatry, report that Single pulse electrical stimulation of the hippocampus is sufficient to impair human episodic memory.

They took 12 people who were undergoing neurosurgery for severe epilepsy, and found that giving a single brief electrical pulse to the hippocampus caused momentary amnesia. Patients were much less likely to remember seeing a word or a picture presented immediately (within 150 milliseconds) after the pulse.

It only worked if you zapped the hippocampus on both the left and the right side simultaneously; if you only disrupt one, memory is unaffected, suggesting that one can compensate for the lack of the other.

It’s been known for 60 years that damage to the hippocampus causes amnesia (e.g.), and previous electrode stimulation studies have shown amnesia after a few minutes of repeated shocks, but this is the first study to show that a single pulse can cause ultra-short memory impairment.

Follow up work confirmed that the stimulation only affected memory, rather than the perception of the items. Stimulation immediately before asking people to remember the items had no effect, showing that the hippocampus is only required for encoding, not retrieval.

This is a great study which adds to our knowledge of the memory functions of the hippocampus – although we need to avoid the temptation to see the hippocampus as purely a “memory module”, since it’s also known to be involved in space perception.

It’s also a good example of why epilepsy patients are the unsung heroes of modern neuroscience – because they’re basically the only people in whom it’s ethical to do this kind of experiments. Surgeons need to stimulate their brains in order to optimize their treatment. It would be unethical to open someone’s skull and poke around their grey matter purely for research purposes, but given that it’s going to happen anyway for medical reasons, you might as well do a little research too…

ResearchBlogging.orgLacruz ME, Valentín A, Seoane JJ, Morris RG, Selway RP, & Alarcón G (2010). Single pulse electrical stimulation of the hippocampus is sufficient to impair human episodic memory. Neuroscience PMID: 20643192

  • SoooIrish!

    Wow, that sounds very science fiction lol

    Possibly a silly question…

    But could that mean a random shock if it were to hit you in just the right place, could make you forget random events?

  • Anonymous

    I would be far more likely to be proud of reading your excellent blog.
    I am sure I am not the only one who greatly appreciates your blogging.

  • Neuroskeptic

    SoooIrish! : Well, if the shock hit your hippocampus, it would mean you didn't remember that moment. But, generally, if you got shocked in the head, it would affect your entire brain and you'd go unconcious, and probably have a seizure.

  • Anonymous

    I would be prouder reading your blog if I wasn't so convinced that this type of experimentation – which is pretty futile in the grand scheme of things – will ultimately be used to manipulate, control and harm people rather than help them.

  • Anonymous

    That's indeed another extremely interesting done with epilepsy patients.

    One small thing though – the memory test applied was a recognition memory. Showing that hippocampal stimulation before the test had no effect on recognition rates does not show that the hippocampus is not needed for retrieval – it is just not needed for recognizing the items in the specific context applied (a finding that fits several theories).

    I wonder what would have been the results for a recall test, or a more associative type of recognition test.

  • SoooIrish!

    I'll show my ignorance of neuroscience further and ask would it be possible for charge to build on mercury fillings and then shock someone from inside the head?

  • Neuroskeptic

    Anonymous: My understanding was that the hippocampus is more often associated with recall, and the overlying cortex, e.g. the perirhinal cortex, is traditionally linked to recognition.

    But maybe the fact that it's recognition in a specific context is what makes it hippocampal. It's also possible that the shocks were also disrupting the overlying cortex, although the authors did try to control for that by stimulating nearby sites and didn't find the same result.

  • Anonymous

    epilepsy.. inmates, concentration/palestine/refugee camps, guantanamo bay, china/falundafa? africa and everywhere else who can't afford ethics committees :) I wouldn't be surprised if that's the region those dirty military scientists stuck those brain chips. I bet they even have an underground quarterly..



No brain. No gain.

About Neuroskeptic

Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.


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