Abstract
Spike timing-dependent plasticity (STDP) has been proposed as a mechanism for optimizing the tuning of neurons to sensory inputs, a process that underlies the formation of receptive field properties and associative memories. The properties of STDP must adjust during development to enable neurons to optimally tune their selectivity for environmental stimuli, but these changes are poorly understood. Here we review the properties of STDP and how these may change during development in primary sensory cortical layers 2/3 and 4, initial sites for intracortical processing. We provide a primer discussing postnatal developmental changes in synaptic proteins and neuromodulators that are thought to influence STDP induction and expression. We propose that STDP is shaped by, but also modifies, synapses to produce refinements in neuronal responses to sensory inputs.
Highlights
A fundamental property of the brain is its ability to change in response to sensory stimuli
While frequency-dependent plasticity has provided a wonderful tool to study the mechanism for the strengthening and weakening of cortical synapses during early stages of development, frequency-dependent plasticity is not sufficient to explain many modifications in synaptic strength that result from changes in sensory experience
It should be noted that timing-dependent LTD (tLTD) in the visual cortex can be induced in a manner thought to rely on postsynaptic NMDA receptors (NMDARs) as the coincidence detector (Froemke et al, 2005; Urakubo et al, 2008), and a similar mechanism is likely to occur in S1
Summary
A fundamental property of the brain is its ability to change in response to sensory stimuli. Adult plasticity in response to sensory deprivation is believed to result primarily from the potentiation of spared (sensory-driven) inputs and not by depression of the lost (sensoryindependent) inputs (Glazewski and Fox, 1996) Both frequency- and spike timing-dependent LTD (tLTD) are difficult to induce following postnatal day 30 (P30) in rodents (Dudek and Bear, 1993; Fox, 2002; Corlew et al, 2007; Banerjee et al, 2009). This suggests that while the ability to strengthen and weaken sensory synapses remains throughout life, changes in synaptic proteins that occur throughout development may influence how plasticity is induced or expressed. STDP has been observed in many neocortical layers (Egger et al, 1999; Sjostrom et al, 2003; Kampa and Stuart, 2006; Letzkus et al, 2006), for simplicity we focus on the synaptic connection between cortical layer (L) 4 and Frontiers in Synaptic Neuroscience www.frontiersin.org
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