|1.3. Hippocampal synaptic plasticity
The hippocampus has been a major experimental system for the studies of synaptic plasticity in the context of putative information-storage mechanisms in the brain. Electrophysiological recordings and molecular imaging studies in animals as well as MRI imaging studies in humans provide correlative evidence that episodic or episodic-like learning and memory involves hippocampal activity (Berger et al., 1983; Duzel et al, 2008; Guzowski et al., 2004; Henke et al., 1997; Maguire., 2001). Its simple laminar pattern of neurons and neural pathways enables the use of extracellular recording techniques to record synaptic events for virtually unlimited periods in vivo (Andersen et al., 1969). Of all the properties of hippocampal synapses, the most important and well documented nature is their ability to respond to specific patterns of activation with long lasting increase or decrease in the synaptic efficacy. LTP, the much studied model of synaptic plasticity, was first identified in the hippocampus and has been extensively characterized using electrophysiological, molecular, biological and biochemical techniques (Bliss et al., 2007; Reymann and Frey, 2007). Recent studies have detected LTP-like changes in hippocampus following learning (Bear et al., 2006; Gruart et al., 2006).
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• Guzowski JF, Knierim JJ, Moser EI (2004) Ensemble dynamics of hippocampal regions CA3 and CA1. Neuron 44:581-584.
• Henke K, Buck A, Weber B, Wieser HG (1997) Human hippocampus establishes associations in memory. Hippocampus 7:249-56.
• Maguire, E.A. (2001) The retrosplenial contribution to human navigation: A review of lesion and neuroimaging findings. Scand. J. Psychol. 42:225–238.
Electrophysiological recordings6 and molecular imaging studies in animals7,8, as well as MRI imaging studies in humans9–11, provide correlative evidence that episodic or episodic-like learning and memory involves hippocampal activity.
Synaptic plasticity in the hippocampus
The hippocampus has been a major experimental system for studies of synaptic plasticity in the context of putative information-storage mechanisms in the brain. Its simple laminar pattern of neurons and neural pathways (FIG. 1) enables the use of extracellular recording techniques to record synaptic events for virtually unlimited periods in vivo12.
6. Berger, T. W., Rinaldi, P. C., Weisz, D. J. & Thompson, R. F. Single-unit analysis of different hippocampal cell types during classical conditioning of rabbit nictitating membrane response. J. Neurophysiol. 50, 1197–1219 (1983).
7. Vazdarjanova, A. & Guzowski, J. F. Differences in hippocampal neuronal population responses to modifications of an environmental context: evidence for distinct, yet complementary, functions of CA3 and CA1 ensembles. J. Neurosci. 24, 6489–6496 (2004).
8. Guzowksi, J. F., Setlow, B., Wagner, E. K. & McGaugh, J. L. Experience-dependent gene expression in the rat hippocampus after spatial learning: a comparison of the immediate-early genes Arc, c‑fos, and zif‑268. J. Neurosci. 21, 5089–5098 (2001).
9. Gabrieli, J. D., Brewer, J. B., Desmond, J. E. & Glover, G. H. Separate neural bases of two fundamental memory processes in the human medial temporal lobe. Science 276, 264–266 (1997).
10. Maguire, E. A. Neuroimaging, memory and the human hippocampus. Rev. Neurol. (Paris) 157, 791–794 (2001).
11. Henke, K., Buck, A., Weber, B. & Wieser, H. G. Human hippocampus establishes associations in memory. Hippocampus 7, 249–256 (1997).