Re: Brain info is high-density

Anders Sandberg (
02 Oct 1999 18:52:41 +0200

"Robert J. Bradbury" <> writes:

> I think we need a quick seminar from Anders on the possible differences
> in how the brain uses LTD & LTP.

Glad to be of help :-)

LTP = Long Term Potentiation occurs when two connected neurons (call them A and B) are active together, especially if the presynaptic neuron A is activated at a high frequency for a while. The signals caused on the B side of the synapse by neuron A will become stronger after this treatment, it has been "potentiated". LTD = Long Term Depression occurs when the presynaptic neuron is activated at a low frequency; this weakens the signal, and we say the synapse has been depressed.

Neuroscientists love the LTP/LTD pair, since they seems to be a reasonable basis for memory implementing Hebb's rule ("neurons that fire together wire together"). LTP makes correlated neurons connect together, while LTD makes anti-correlated neurons decrease their connections. With just LTP, the network would likely work less well because synapses would be "filled up" and cannot easily be re-used, while LTD enables erasure as things change. In fact, some studies suggest that LTD is more important than LTP for certain tasks; I'm not sure about that one yet.

Anders Sandberg                                      Towards Ascension!                  
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y