Thursday, September 10, 2009

Why fear memories are hard to erase.

Gogolla et al. present evidence that fear memories are protected from erasure (extinction) by an matrix of compounds (chondroitin sulfate proteoglycans) outside of nerve cells in the amygdala, ie. in the extra-cellular matrix:
In adult animals, fear conditioning induces a permanent memory that is resilient to erasure by extinction. In contrast, during early postnatal development, extinction of conditioned fear leads to memory erasure, suggesting that fear memories are actively protected in adults. We show here that this protection is conferred by extracellular matrix chondroitin sulfate proteoglycans (CSPGs) in the amygdala. The organization of CSPGs into perineuronal nets (PNNs) coincided with the developmental switch in fear memory resilience. In adults, degradation of PNNs by chondroitinase ABC specifically rendered subsequently acquired fear memories susceptible to erasure. This result indicates that intact PNNs mediate the formation of erasure-resistant fear memories and identifies a molecular mechanism closing a postnatal critical period during which traumatic memories can be erased by extinction.
These results, together with previous experiments in the visual cortex on visual plasticity, suggest that maturation of the extracellular matrix could be a mechanism used by different brain circuits to change from a malleable to a more crystallized state during development. The presence of a high concentration of CSPGs in the perineuronal nets surrounding inhibitory neurons suggests that inhibitory circuits could play an important role in the developmental control of plasticity.


  1. Anonymous5:47 AM

    Amazing. Soon it will be more simple to remember what molecules do NOT affect memory.

  2. Anonymous9:19 AM

    Is there a certain age where this happens?
    For instance is there a certain age that you could rescue a child from a bad situation and erase all the negative by positive conditioning? Then they reach a certain age and it is just there....

  3. I should have mentioned in the post that the experiments are done with rats, and three weeks of age is when they begin to loose their ability to extinguish aversive memories. The work is surely applicable to humans, but hasn't been extended to them. I don't know the age for humans at which aversive memories can no longer be extinguished.

  4. A new study on mice uncovers some answers that could someday offer a potent target for eliminating the recurrence of bad memories in humans, especially known to those who suffer from post-traumatic stress disorder (PTSD).

    "Fear memories are the most robust memories—they can last over a lifetime," says Nadine Gogolla, a biologist at Harvard University and lead author on the paper published today in the journal Science. "You can push them far back, but spontaneous recovery and relapses will happen." Until now, science has been unable to stop this process—in humans or in mice.