Biophysical and Biochemical Records of Associative Memory in Rabbit CA1 Pyramidal Neurons and Hermissenda B Cells
Joseph L. Lo Turco James L. Olds Barry Bank Daniel L. Alkon National Institutes of Health
Associative memory, the storage of learned relationships, is a fundamental function of the central nervous system. Cellular correlates of learned behaviors are traces of associative memory, and as such represent elementary units of memory storage. Whereas there has been success in identifying elementary units of associative memory in mulluscan neurons, particularly in Hermissenda B cells ( Alkon , 1984, Alkon et al., 1985, Lederhendeler & Farley, 1985, Nelson et al., 1990, Collin et al., 1991), technical limitations have impeded identification in mammalian neurons ( Brons & Woods, 1980; Tsukahara et al., 1981). To overcome methodological difficulties presented by the mammalian brain, we have capitalized on inherent advantages offered by the in vitro brain slices technique (see Dingledine, 1982), the quantitative autoradiographic technique (see Pan, 1985), and a robust form of associative learning: classical conditioning of the rabbit eyeblink response (see Gormezano et al., 1986). By combining these methodologies, we have recently identified biophysical and biochemical correlates of associative learning in rabbit hippocampal CA1 neurons.
In this chapter we review the cellular correlates of classical conditioning that have been identified in rabbit hippocampal; CA 1cells and in Hermissenda B cells. The remarkable similarities between records of learning in these cell types are discussed. Based on these similarities we propose a general mechanism for the storage of associative information.
Classical conditioning, a prototypical form of associative learning is an ideal behavioral paradigm for the biological analysis of elementary learning processes.