<unk> is "the alteration of nerve activity through targeted delivery of a stimulus, such as electrical stimulation or chemical agents, to specific neurological sites in the body". It is carried out to normalize – or modulate – nervous tissue function.<unk> is an evolving therapy that can involve a range of electromagnetic stimuli such as a magnetic field (rTMS), an electric current, or a drug instilled directly in the subdural space (intrathecal drug delivery). Emerging applications involve targeted introduction of genes or gene regulators and light (optogenetics), and by 2014, these had been at minimum demonstrated in mammalian models, or first-in-human data had been acquired. The most clinical experience has been with electrical stimulation.<unk>  whether electrical or magnetic, employs the body's natural biological response by stimulating nerve cell activity that can influence populations of nerves by releasing transmitters, such as dopamine, or other chemical messengers such as the peptide Substance P, that can modulate the excitability and firing patterns of neural circuits. There may also be more direct electrophysiological effects on neural membranes as the mechanism of action of electrical interaction with neural elements. The end effect is a "normalization" of a neural network function from its perturbed state. Presumed mechanisms of action for neurostimulation include depolarizing blockade, stochastic normalization of neural firing, axonal blockade, reduction of neural firing keratosis, and suppression of neural network oscillations. Although the exact mechanisms of neurostimulation are not known, the empirical effectiveness has led to considerable application clinically. Existing and emerging<unk> treatments also include application in medication-resistant epilepsy, chronic head pain conditions, and functional therapy ranging from bladder and bowel or respiratory control to improvement of sensory deficits, such as hearing (cochlear implants and auditory brainstem implants) and vision (retinal implants). Technical improvements include a trend toward minimally invasive (or noninvasive) systems; as well as smaller, more sophisticated devices that may have automated feedback control, and conditional compatibility with magnetic resonance imaging.<unk> therapy has been investigated for other chronic conditions, such as Alzheimer's disease, depression, chronic pain, and as an adjunctive treatment in recovery from stroke.
Neuromodulation 
Neurosecretion
Remyelination
Vasculogenesis
Reinnervation
Lymphangiogenesis
Neuroregeneration
Arteriogenesis