LTP and LTD
Although there are many ways to modulate neuronal function, they are not usually linked to specific psychological functions. But neuromodulators neurochemicals that indirectly affect neuronal activity, usually by modifying response to other chemical neurotransmitters paracrine non-classical effects of neurotransmitters that may not be released at the synapse, and/or whose receptors are not located at the synapse neurocrine classical neurochemical action of transmitters that are released at the axon terminal to affect specialized receptor sites across the synaptic cleft there is one form of synaptic modifiability that has led researchers to make striking and specific claims, presenting it as a possible neural basis for some forms of learning or the ability to lay down new memories. The first crucial observation was made by electrophysiologists studying the responses of cells in the hippocampus, a structure that is crucial in memory processing. They found that the size of the neuronal response to a single pulse of electrical stimulation at a given intensity could be increased, in a long-lasting way, by giving a relatively brief burst of high frequency stimulation. By comparing the size of the response to a single pulse before and after this high frequency series of pulses, researchers showed beyond doubt that neuronal responsiveness had increased. This change is called longterm potentiation, or LTP. It is now clear that LTP can be seen in many structures in the brain, and not only those thought to be associated with memory. It is highly likely, though, that LTP always reflects experience-dependent changes in neuronal functioning, whether in the sensitization produced by painful stimuli, or in perceptual development in the visual cortex, or in the laying down of memory traces in the brain. It has also become clear that there is a complementary process – long-term depression, or LTD – which describes a decrease in neuronal response. The ability either to increase or to decrease synaptic connectivity as appropriate offers maximum flexibility for adjusting neuronal function.
[Tim Bliss (1940– ) and Terje Lømo (1935– ) first reported the phenomenon of long-term potentiation. The plausibility that a strengthening of synapses might underlie memory storage increased tremendously when the phenomenon of long-term potentiation (LTP) was discovered by these two researchers. In the 1970s, Bliss and Lømo noticed that if they applied a few seconds of high frequency electrical stimulation to certain neurons in the rabbit hippocampus, synaptic transmissions to those neurons would increase in amplitude. More surprisingly, this enhancement seemed to be long-lasting, sometimes persisting for weeks (Bliss & Lømo, 1973). This phenomenon has since been termed long-term potentiation, or LTP. In the twenty years since its discovery, a great debate has raged among neuroscientists about whether this LTP might be the crucial mechanism underpinning learning and memory.]
Although there are many ways to modulate neuronal function, they are not usually linked to specific psychological functions. But neuromodulators neurochemicals that indirectly affect neuronal activity, usually by modifying response to other chemical neurotransmitters paracrine non-classical effects of neurotransmitters that may not be released at the synapse, and/or whose receptors are not located at the synapse neurocrine classical neurochemical action of transmitters that are released at the axon terminal to affect specialized receptor sites across the synaptic cleft there is one form of synaptic modifiability that has led researchers to make striking and specific claims, presenting it as a possible neural basis for some forms of learning or the ability to lay down new memories. The first crucial observation was made by electrophysiologists studying the responses of cells in the hippocampus, a structure that is crucial in memory processing. They found that the size of the neuronal response to a single pulse of electrical stimulation at a given intensity could be increased, in a long-lasting way, by giving a relatively brief burst of high frequency stimulation. By comparing the size of the response to a single pulse before and after this high frequency series of pulses, researchers showed beyond doubt that neuronal responsiveness had increased. This change is called longterm potentiation, or LTP. It is now clear that LTP can be seen in many structures in the brain, and not only those thought to be associated with memory. It is highly likely, though, that LTP always reflects experience-dependent changes in neuronal functioning, whether in the sensitization produced by painful stimuli, or in perceptual development in the visual cortex, or in the laying down of memory traces in the brain. It has also become clear that there is a complementary process – long-term depression, or LTD – which describes a decrease in neuronal response. The ability either to increase or to decrease synaptic connectivity as appropriate offers maximum flexibility for adjusting neuronal function.
[Tim Bliss (1940– ) and Terje Lømo (1935– ) first reported the phenomenon of long-term potentiation. The plausibility that a strengthening of synapses might underlie memory storage increased tremendously when the phenomenon of long-term potentiation (LTP) was discovered by these two researchers. In the 1970s, Bliss and Lømo noticed that if they applied a few seconds of high frequency electrical stimulation to certain neurons in the rabbit hippocampus, synaptic transmissions to those neurons would increase in amplitude. More surprisingly, this enhancement seemed to be long-lasting, sometimes persisting for weeks (Bliss & Lømo, 1973). This phenomenon has since been termed long-term potentiation, or LTP. In the twenty years since its discovery, a great debate has raged among neuroscientists about whether this LTP might be the crucial mechanism underpinning learning and memory.]
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