title: Intracortical Microstimulation Parameters Dictate the Amplitude and Latency of Evoked Responses.
abstract: BACKGROUND
  Microstimulation of brain tissue plays a key role in a variety of sensory prosthetics, clinical therapies and research applications. However, the effects of stimulation parameters on the responses they evoke remain widely unknown.
  
  
  OBJECTIVE
  We aimed to investigate the contribution of each stimulation parameter to the response and identify interactions existing between parameters.
  
  
  METHODS
  Parameters of the constant-current, biphasic square waveform were examined in acute terminal experiments under ketamine anaesthesia. The motor cortex of 7 Sprague-Dawley rats was stimulated while recording motor evoked potentials (MEP) from the forelimb. Intracortical microstimulation (ICMS) parameters were systematically tested in a pair-wise fashion to observe the influence of each parameter on the amplitude and latency of the MEP.
  
  
  RESULTS
  The amplitude of the MEP increased continually with stimulus amplitude (p < 0.001) and pulse duration (p = 0.001) throughout the range tested. Increases were also observed when stimuli were raised from low to moderate values of frequency (p = 0.022) and train duration (p = 0.045), after which no further excitation occurs. The latency of MEP initiation decreased when stimulus amplitude (p = 0.037) and frequency (p = 0.001) were raised from low to moderate values, after which the responses plateaued. MEP latencies were further reduced by increasing the pulse duration (p = 0.011), but train duration had no effect.
  
  
  CONCLUSIONS
  Our data indicate that MEP amplitude and onset latency can be modulated by alterations to a number of stimulus parameters, even in restrictive paradigms, and suggest that the parameters of the standard ICMS signal used for evoking movements from the motor cortex can be further optimized.
authors.affiliation: Polystim Neurotechnologies, Institute of Biomedical Engineering, Polytechnique, Montreal, Quebec, Canada; Département de Neurosciences, Faculté de Médecine, Université de Montréal, Montreal, Quebec, Canada. Electronic address: meghan.watson@polymtl.ca.
authors.forename: Meghan
authors.initials: M
authors.lastname: Watson
authors.affiliation: Département de Neurosciences, Faculté de Médecine, Université de Montréal, Montreal, Quebec, Canada.
authors.forename: Numa
authors.initials: N
authors.lastname: Dancause
authors.affiliation: Polystim Neurotechnologies, Institute of Biomedical Engineering, Polytechnique, Montreal, Quebec, Canada.
authors.forename: Mohamad
authors.initials: M
authors.lastname: Sawan
mesh_terms: D000818:Animals; D004558:Electric Stimulation / Q000379:methods*; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D023421:Models, Animal; D009044:Motor Cortex / Q000502:physiology; D009068:Movement / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
keywords: Intracortical microstimulation; Motor evoked potentials; Stimulation parameters