of long-term potentiation, however these concepts are generally considered types of synaptic plasticity. Homeostatic and Hebbian plasticity Central nervous system (CNS) neurons integrate signals from many neurons. In the short term, it is important to have changes in activity of the neuron because this is how information is conveyed in the nervous system (Hebbian plasticity). However, for long-term sustainability, drift towards excitability or inexcitability will disturb the circuit's ability to convey information (homeostatic plasticity). Long-term potentiation (LTP) induces a higher firing rate in post synaptic neurons. It has been hypothesized that the intrinsic properties of a neuron should be arranged to make the most of the dynamic range, acting as a homeostatic mechanism. However, it was shown that intrinsic excitability follows a lognormal distribution which requires active, Hebbian learning to be kept up. In vitro studies have found that when the spontaneous activity of neuronal cultures is inhibited, the neurons become hyper excitable and that when an increase in activity is induced for long periods, the firing rates of the culture drop. In contrast, there is a wealth of evidence that the opposite form of regulation, Hebbian learning or LTP-IE/LTD-IE, also occurs and theoretical arguments show that Hebbian plasticity must be the dominant form of plasticity for intrinsic excitability as well. Since homeostatic plasticity also occurs between individual synapses, an earlier view suggesting that homeostatic plasticity and intrinsic plasticity are linked was shown to be inconsistent with evidence. Mechanism One mechanism for preserving the dynamic range of a neuron is synaptic scaling, a homeostatic form of plasticity that restores neuronal activity to its normal 'baseline' levels by changing the postsynaptic response of synapses of a neuron as a function of activity. Homeostatic modulation of the intrinsic excitability of a neuron is another way to maintain stability. The regulation of ionic conductances can be achieved in a number of ways, mostly through the release of neuromodulators like dopamine, serotonin etc. Another way is through the controlled release of brain-derived neurotrophic factor (BDNF). BDNF has also been found to influence synaptic scaling, suggesting that this neurotrophic factor may be responsible for the coordination of synaptic and nonsynaptic mechanisms in homeostatic plasticity. Dendritic excitability The dendrites are the regions responsible for the integration of the inputs from other neurons. One way that neurons manipulate the integration properties of the dendrites is by changing the number and properties of voltage gated ion channels. Inducing