Synaptic scaling refers to global adjustments of all synapses in a neuron or a neuronal network in response to global changes in activity. These adjustments manifest either as changes in synapse number or in post synaptic electrical currents (defined here as “synaptic efficacy”) [6–8, 24]. They are considered homeostatic because they restore total synaptic inputs to a specific range while maintaining the relative strength of all synapses. Synapses can be “downscaled” and “upscaled” which is thought to offset Hebbian changes that if left unchecked would quickly saturate synaptic strength in a network [6–8]. Because synaptic scaling involves global changes in synapses, rather than input-specific change at a given synapse, it is considered non-Hebbian. More recent work suggests that synaptic scaling can also occur regionally (i.e., “local” scaling) but since this is less understood, it is not discussed further here [6–8, 24]. In addition, there is increasing evidence that synaptic scaling also occurs in inhibitory circuits [6–8]. However, as inhibitory synapses do not factor prominently in SHY [9, 10], inhibitory scaling is also not discussed.
The central principle of synaptic scaling is quite simple: decreases in neuronal or network activity upscale synapses while increases in neuronal or network activity downscale synapses. This principle is key to our later discussion of the mechanisms of SHY. The first demonstration of synaptic scaling was made in cell culture where drugs that inhibited neuronal activity (e.g., tetrodotoxin) led to upscaling while drugs that increased neuronal activity (e.g., bicuculine) led to downscaling [6–8]. The effects of synaptic scaling manifested as changes in the frequency or amplitude of miniature excitatory postsynaptic currents (mEPSCs). More recent studies suggest that synaptic scaling also occurs in vivo under more naturalistic manipulations. For example, sensory deprivation in vivo leads to compensatory synaptic upscaling (reviewed in [6]) as measured by changes in dendrite spine morphology [25] and cortical mEPSCs [26]. In addition, although early in vitro studies suggested that scaling was a slow process (occurring over 24–48 hours [27]), more recent findings demonstrate that it can occur much more rapidly (over minutes [28]).
Synaptic scaling refers to global adjustments of all synapses in a neuron or a neuronal network in response to global changes in activity. These adjustments manifest either as changes in synapse number or in post synaptic electrical currents (defined here as “synaptic efficacy”) [6–8, 24]. They are considered homeostatic because they restore total synaptic inputs to a specific range while maintaining the relative strength of all synapses. Synapses can be “downscaled” and “upscaled” which is thought to offset Hebbian changes that if left unchecked would quickly saturate synaptic strength in a network [6–8]. Because synaptic scaling involves global changes in synapses, rather than input-specific change at a given synapse, it is considered non-Hebbian. More recent work suggests that synaptic scaling can also occur regionally (i.e., “local” scaling) but since this is less understood, it is not discussed further here [6–8, 24]. In addition, there is increasing evidence that synaptic scaling also occurs in inhibitory circuits [6–8]. However, as inhibitory synapses do not factor prominently in SHY [9, 10], inhibitory scaling is also not discussed.The central principle of synaptic scaling is quite simple: decreases in neuronal or network activity upscale synapses while increases in neuronal or network activity downscale synapses. This principle is key to our later discussion of the mechanisms of SHY. The first demonstration of synaptic scaling was made in cell culture where drugs that inhibited neuronal activity (e.g., tetrodotoxin) led to upscaling while drugs that increased neuronal activity (e.g., bicuculine) led to downscaling [6–8]. The effects of synaptic scaling manifested as changes in the frequency or amplitude of miniature excitatory postsynaptic currents (mEPSCs). More recent studies suggest that synaptic scaling also occurs in vivo under more naturalistic manipulations. For example, sensory deprivation in vivo leads to compensatory synaptic upscaling (reviewed in [6]) as measured by changes in dendrite spine morphology [25] and cortical mEPSCs [26]. In addition, although early in vitro studies suggested that scaling was a slow process (occurring over 24–48 hours [27]), more recent findings demonstrate that it can occur much more rapidly (over minutes [28]).
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