NeuroStim

Neurostimulation is the purposeful modulation of the nervous system's activity using invasive (e.g. microelectrodes) or non-invasive means (e.g. transcranial magnetic stimulation or transcranial electric stimulation, tES, such as tDCS or transcranial alternating current stimulation, tACS). Neurostimulation usually refers to the electromagnetic approaches to neuromodulation.

Neurostimulation technology can improve the life quality of those who are severely paralyzed or have profound losses to various sense organs, as well as for permanent reduction of severe, chronic pain which would otherwise require constant (around-the-clock), high-dose opioid therapy (such as neuropathic pain and spinal-cord injury). It serves as the key part of neural prosthetics for hearing aids, artificial vision, artificial limbs, and brain-machine interfaces. In the case of neural stimulation, mostly an electrical stimulation is utilized and charge-balanced biphasic constant current waveforms or capacitively coupled charge injection approaches are adopted. Alternatively, transcranial magnetic stimulation and transcranial electric stimulation have been proposed as non-invasive methods in which either a magnetic field or transcranially applied electric currents cause neurostimulation.^[1][2]

Brain stimulation

Brain stimulation has potentials to treat some disorders such as epilepsy. In this method, scheduled stimulation is applied to specific cortical or subcortical targets. There are available commercial devices^[3] that can deliver an electrical pulse at scheduled time intervals. Scheduled stimulation is hypothesized to alter the intrinsic neurophysiologic properties of epileptic networks. The most explored targets for scheduled stimulation are the anterior nucleus of the thalamus and the hippocampus. The anterior nucleus of the thalamus has been studied, which has shown a significant seizure reduction with the stimulator on versus off during several months after stimulator implantation.^[4] Moreover, the cluster headache (CH) can be treated by using a temporary stimulating electrode at sphenopalatine ganglion (SPG). Pain relief is reported within several minutes of stimulation in this method.^[5] To avoid use of implanted electrodes, researchers have engineered ways to inscribe a "window" made of zirconia that has been modified to be transparent and implanted in mice skulls, to allow optical waves to penetrate more deeply, as in optogenetics, to stimulate or inhibit individual neurons.^[6]

Deep brain stimulation

Deep brain stimulation (DBS) has shown benefits for movement disorders such as Parkinson's disease, tremor and dystonia and affective disorders such as depression, obsessive-compulsive disorder, Tourette syndrome, chronic pain and cluster headache. DBS can directly change the brain activity in a controlled manner and is hence used to map fundamental mechanisms of brain functions along with neuroimaging methods.

A DBS system consists of three components: the implanted pulse generator (IPG), the lead, and an extension. The implantable pulse generator (PG) generates stimulation pulses, which are sent to intracranial leads at the target via an extension. The simulation pulses interfere with neural activity at the target site.

The application and effects of DBS, on both normal and diseased brains, involves many parameters. These include the physiological properties of the brain tissue, which may change with disease state. Also important are the stimulation parameters, such as amplitude and temporal characteristics, and the geometric configuration of the electrode and the tissue that surrounds it.

In spite of a huge number of studies on DBS, its mechanism of action is still not well understood. Developing DBS microelectrodes is still challenging.^[7]

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