The Organization for Computational Neuroscience has started a survey, asking people for their submissions, and here is my contribution:
Prediction: The basis for learning and memory exists primarily within the single neuron.
Rationale: (A) Dendrites/axons are adaptive, in particular the expression and contribution of ion channels adapts to use. This also extends to synaptic channels. (B) The decision on transforming a transient calcium signal into a permanent trace lies within the single neuron, within its protein signaling network and DNA readout mechanisms. The neuron’s memory traces are both use-dependent (dependent on shape and size of calcium signals received) and subject to additional internal computations, e.g. involving kinases/phosphatases, early genes, histones etc.
Remote memories are not coded by current synaptic connectivity, but internally by clusters of neurons, which become activated under certain conditions.
Conclusion: Memory research has to focus on the cellular (neuronal) basis of adaptation, synaptic connectivity will be predictable from adequate neuron models.
The statement in italics is extra. I have no papers, no references on that. For the rest, cf.
Scheler G. Regulation of neuromodulator receptor efficacy–implications for whole-neuron and synaptic plasticity. Prog Neurobiol. 2004 Apr;72(6):399-415. PMID: 15177784
Scheler G. Learning intrinsic excitability in medium spiny neurons. F1000Res. 2013 Mar 14 2:88. doi: 10.12688/f1000research.2-88.v2. eCollection 2013. PMID: 25520776
Scheler, G: Logarithmic distributions prove that intrinsic learning is Hebbian. F1000Res. 2017 (August).