https://www.cell.com/trends/neurosciences/pdf/0166-2236(87)90011-7.pdf

Hippocampal synaptic enhancement and information storage within a distributed memory system

How the brain codes, stores, and retrieves memories is among the most important and baffling questions in science. The uniqueness of each human being is due largely to the memory store—the biological residue of memory from a lifetime of experience. The cellular basis of this ability to learn can be traced to simpler organisms. In the past generation, understanding of the biological basis of learning and memory has undergone a revolution. It is clear that various forms and aspects of learning and memory involve particular systems, networks, and circuits in the brain, and it now appears possible to identify these circuits, localize the sites of memory storage, and analyze the cellular and molecular mechanisms of memory.

Learning and memory

History and Definition In 1973, two reports appeared in the Journal of Physiology that described a long-term potentiation (L TP) of synaptic transmission at a monosynaptic junction in the mammalian eNS. These two papers, one dealing with the anesthetized rabbit preparation (Bliss & L0mo 1973) and the other dealing with the unanesthetized rabbit (Bliss & Gardner-Medwin 1973), were of considerable interest because they marked the first demonstration of a neurophysiological alteration in the mammalian brain possessing a con­ siderable time-course. Prior to these observations, neurophysiological phenomena were known to be of relatively modest temporal extent. The experiments of Bliss and colleagues showed that in the perforant path to dentate gyrus synapse, substantial increases in synaptic efficacy were observed following tetanic stimulation of afferent fibers. Synaptic efficacy refers to the postsynapti c response to a constant afferent volley. The changes (on the order of a 50% increase in the amplitude of the response) lasted for at least ten hours in the anesthetized preparation and up to 16 weeks in the unanesthetized preparation following a series of tetanic stimuli . These results attracted great interest because of the possi­ bility that the phenomenon might underlie some aspects of memory storage. A critical question-not yet completely answered-was stated by Bliss & Lemo : "Whether or not the intact animal makes use in real life of a property which has been revealed by synchronous, repetitive volleys to a population of fibers the normal and pattern of activity along which are unknown, is another matter" (Bliss & L0mo 1973, p. 355). As we shall see, the available evidence suggests that L TP does occur in conjunction with behavioral learning-although whether it is necessary and sufficient is far from certain.

Long-term potentiation.

Recent studies have uncovered a synaptic process with properties required for an intermediate step in memory storage. Calcium rapidly and irreversibly increases the number of receptors for glutamate (a probable neurotransmitter) in forebrain synaptic membranes by activating a proteinase (calpain) that degrades fodrin, a spectrin-like protein. This process provides a means through which physiological activity could produce long-lasting changes in synaptic chemistry and ultrastructure. Since the process is only poorly represented in the brain stem, it is hypothesized to be responsible for those forms of memory localized in the telencephalon.

https://science.sciencemag.org/content/sci/224/4653/1057.full.pdf

The Biochemistry of Memory: A New and Specific Hypothesis.

Dendritic spines, the tiny protrusions that stud the surface of many neurons, are the location of over 90% of all excitatory synapses that occur in the CNS. Their small size has, in large part, made them refractory to conventional experimental approaches. Yet their widespread occurrence and likely involvement in learning and memory has motivated extensive efforts to obtain quantitative descriptions of spines in both steady state and dynamic onditions. Since the seminal mathematical analyses of D’Arcy Thompson (1992), the power of quantitatively establishing key parameters of structure has become recognized as a foundation of successful biological inquiry. For dendritic spines, highly precise determinations of structure and its variation are again proving to be essential for establishing a valid concept of function. The recent conjunction of high quality information about the structure, function, and theoretical implications of dendritic spines has, in fact, produced a flurry of

/pdf/dendritic-spines-cellular-specializations-imparting-both-1z7o0tvz8w.pdf

S. Hafner

Papers

Long-term potentiation phenomena in the rat limbic forebrain