The relative impact of microstimulation parameters on movement generation

Abstract

Microstimulation is widely used in neurophysiology to characterize brain areas with behavior and in clinical therapeutics to treat neurological disorder. Current intensity and frequency, which respectively influence activation patterns in spatial and temporal domains, are typically selected to elicit a desired response, but their effective influence on behavior has not been thoroughly examined. We delivered microstimulation to the primate superior colliculus while systematically varying each parameter to capture effects of a large range of parameter space. We found that frequency was more effective in driving output properties, whereas properties changed gradually with intensity. Interestingly, when different parameter combinations were matched for total charge, effects on behavioral properties became seemingly equivalent. This study provides a first level resource for choosing desired parameter ranges to effectively manipulate behavior. It also provides insights into interchangeability of parameters, which can assist clinical microstimulation that looks to appropriately control behavior within designated constraints, such as power consumption.

Blink Perturbation Effects on Saccades Evoked by Microstimulation of the Superior Colliculus

“…Next, low stimulation settings were obtained by selecting lower current intensities, frequencies, or both that reliably produced movements (>90% probability of evoking movement). This experimental manipulation also reduced the amplitude of the movements consistently (∼15% or more change in amplitude), as described by previous studies [14], [15], [16], [17]. The sub-optimal stimulation setting could be as low as 10 µA and 100 Hz and differed across sites.…”

“…There is a modest initial suppression linked to the time of puff, which is likely mediated through the trigeminocollicular projection [19], but the pronounced attenuation is observed when the saccadic eye movement overlaps with the BREM. Furthermore, we expect that this relationship applies also for saccades evoked by suboptimal stimulation because, as we have argued recently [17], the population SC output is most likely not entrained to the stimulation train. Instead, it likely reflects a network level response that is comparable for stimulation-evoked and target-activated responses.…”

“…We have argued recently [17] that during microstimulation, network properties within the SC dominate the stimulation-induced pulse train and produce a population level response that largely resembles that associated with target-directed saccades. Furthermore, the vigor of activity changes with stimulation parameters, much like the population activity is modulated by the presence or absence of a visual target [27].…”

“…Furthermore, the vigor of activity changes with stimulation parameters, much like the population activity is modulated by the presence or absence of a visual target [27]. Accordingly, saccades evoked by supra-threshold stimulation obey main-sequence properties, whereas movements evoked by sub-optimal parameters exhibit lower peak velocities [14], [15], [16], [17]. Our insight, however, does not discount the possibility that a subset of neurons within the population do emit a spike for each pulse delivered through the electrode and that the entrainment could become the dominant component for high stimulation parameters, such as when stimulation evokes stair-case saccades with a constant velocity movement during the inter-saccadic intervals [28], [29].…”

Comparing temporal aspects of visual, tactile, and microstimulation feedback for motor control

“…Early in experiments, we designed microstimulation parameters using a range of amplitudes (30–90µA) with a fixed duration (500ms) and a range of durations (50–500ms) with fixed amplitude (90µA) (black points in figure 2) [58]. We used a stimulus detection task (section 2.2.3) in which the go cue was microstimulation.…”