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Long-Term Potentiation: What's Learning Got To Do With It?

Shors, Tracey J. and Matzel, Louis D. (1997) Long-Term Potentiation: What's Learning Got To Do With It?.

Short Abstract:

Long-term potentiation (LTP) is operationally defined as a long-lasting increase in synaptic efficacy which follows high-frequency stimulation of afferent fibers. Since the first full description of the phenomenon in 1973, exploration of the mechanisms underlying LTP induction has been one of the most active areas of research in neuroscience. Of principal interest to those who study LTP, particularly LTP in the mammalian hippocampus, is its presumed role in the establishment of stable memories, a role consistent with "Hebbian" descriptions of memory formation. Other characteristics of LTP, including its rapid induction, persistence, and correlation with natural brain rhythms, provide circumstantial support for this connection to memory storage. Nonetheless, there is little empirical evidence that directly links LTP to the storage of memories. In this commentary, we review a range of cellular and behavioral characteristics of LTP, and evaluate whether those characteristics are consistent with the purported role of hippocampal LTP in memory formation. We suggest that much of the present focus on LTP reflects a preconception that LTP is a learning mechanism, although the empirical evidence often suggests that LTP is unsuitable for such a role. As an alternative to serving as a memory storage device, we propose that LTP may serve as a neural equivalent to an arousal or attention device in the brain. Accordingly, LTP is suggested to nonspecifically increase the effective salience of discrete external stimuli and thereby is capable of facilitating the induction of memories at distant synapses. In an environment open to critical inquiry, other hypotheses regarding the functional utility of this intensely studied mechanism are conceivable; the intent of this article is not exclusively to promote a single hypothesis, but rather to stimulate discussion about the neural mechanisms that are likely to underlie memory storage, and to appraise whether LTP can reasonably be considered a viable candidate for such a mechanism.

Long Abstract:

Long-term potentiation (LTP) is operationally defined as a long-lasting increase in synaptic efficacy which follows high-frequency stimulation of afferent fibers. Since the first full description of the phenomenon in 1973, exploration of the mechanisms underlying LTP induction has been one of the most active areas of research in neuroscience. Of principal interest to those who study LTP, particularly LTP in the mammalian hippocampus, is its presumed role in the establishment of stable memories, a role consistent with "Hebbian" descriptions of memory formation. Other characteristics of LTP, including its rapid induction, persistence, and correlation with natural brain rhythms, provide circumstantial support for this connection to memory storage. Nonetheless, there is little empirical evidence that directly links LTP to the storage of memories. In this commentary, we review a range of cellular and behavioral characteristics of LTP, and evaluate whether those characteristics are consistent with the purported role of hippocampal LTP in memory formation. We suggest that much of the present focus on LTP reflects a preconception that LTP is a learning mechanism, although the empirical evidence often suggests that LTP is unsuitable for such a role. As an alternative to serving as a memory storage device, we propose that LTP may serve as a neural equivalent to an arousal or attention device in the brain. Accordingly, LTP is suggested to nonspecifically increase the effective salience of discrete external stimuli and thereby is capable of facilitating the induction of memories at distant synapses. In an environment open to critical inquiry, other hypotheses regarding the functional utility of this intensely studied mechanism are conceivable; the intent of this article is not exclusively to promote a single hypothesis, but rather to stimulate discussion about the neural mechanisms that are likely to underlie memory storage, and to appraise whether LTP can reasonably be considered a viable candidate for such a mechanism.

Keywords:	NMDA, synaptic plasticity, Hebbian synapses, calcium, hippocampus, theta rhythm, spatial learning, classical conditioning, attention, arousal, memory systems
Subjects:	Psychology: Cognitive Psychology Psychology: Learning and Memory Neuroscience: Neuroanatomy Neuroscience: Neurochemistry Neuroscience: Neuroendocrinology Neuroscience: Neurology Neuroscience: Neurophysiology
ID code:	bbs00000482
Deposited by:	Tracey Shors on 01 May 2001