tissue. lastly, they are more easily fabricated into different tip shapes and sizes at large quantities. platinum electrodes are platinum black plated and insulated with glass. "they normally give stable recordings, a high signal-to-noise ratio, good isolation, and they are quite rugged in the usual tip sizes". the only limitation is that the tips are very fine and fragile. silicon electrodes are alloy electrodes doped with silicon and an insulating glass cover layer. silicon technology provides better mechanical stiffness and is a good supporting carrier to allow for multiple recording sites on a single electrode. tungsten electrodes are very rugged and provide very stable recordings. this allows manufacturing of tungsten electrodes with very small tips to isolate high-frequencies. tungsten, however, is very noisy at low frequencies. in mammalian nervous system where there are fast signals, noise can be removed with a high-pass filter. slow signals are lost if filtered so tungsten is not a good choice for recording these signals. applications single-unit recordings have allowed the ability to monitor single-neuron activity. this has allowed researchers to discover the role of different parts of the brain in function and behavior. more recently, recording from single neurons can be used to engineer "mind-controlled" devices. cognitive science noninvasive tools to study the cns have been developed to provide structural and functional information, but they do not provide very high resolution. to offset this problem invasive recording methods have been used. single unit recording methods give high spatial and temporal resolution to allow for information assessing the relationship between brain structure, function, and behavior. by looking at brain activity at the neuron level, researchers can link brain activity to behavior and create neuronal maps describing flow of information through the brain. for example, boraud et al. report the use of single unit recordings to determine the structural organization of the basal ganglia in patients with parkinson's disease. evoked potentials provide a method to couple behavior to brain function. by stimulating different responses, one can visualize what portion of the brain is activated. this method has been used to explore cognitive functions such as perception, memory, language, emotions, and motor control. brain–machine interfaces brain–machine interfaces (bmis) have been developed within the last 20 years. by recording single unit potentials, these devices can decode signals through a computer and output this signal for control of an external device such as a computer cursor or prosthetic limb. bmis have the potential to restore function in patients with paralysis or neurological disease. this technology has potential to reach a wide variety of patients but is not yet available clinically due to lack of reliability in recording signals over time. the primary hypothesis regarding this failure is that the chronic inflammatory response around the electrode causes neurodegeneration that reduces the number of neurons it is able to record from (nicolelis, 2001). in 2004, the braingate pilot clinical trial was initiated to "test the safety and feasibility of a neural interface system based on an intracortical 100-electrode silicon recording array". this initiative has been successful in advancement of bcis and in 2011, published data showing long term computer control in a patient with tetraplegia (simeral, 2011).