Perception of microstimulation frequency in human somatosensory cortex

Microstimulation in the somatosensory cortex can evoke artificial tactile percepts and can be incorporated into bidirectional brain-computer interfaces (BCIs) to restore function after injury or disease. However, little is known about how stimulation parameters themselves affect perception. Here, we stimulated through microelectrode arrays implanted in the somatosensory cortex of two human participants with cervical spinal cord injury and varied the stimulus amplitude, frequency and train duration. Increasing the amplitude and train duration increased the perceived intensity on all tested electrodes. Surprisingly, we found that increasing the frequency evoked more intense percepts on some electrodes but evoked less intense percepts on other electrodes. These different frequency-intensity relationships were divided into three groups which also evoked distinct percept qualities at different stimulus frequencies. Neighboring electrode sites were more likely to belong to the same group. These results support the idea that stimulation frequency directly controls tactile perception and that these different percepts may be related to the organization of somatosensory cortex, which will facilitate principled development of stimulation strategies for bidirectional BCIs.

SHORT-TERM EFFECTS OF SELECTIVE TRANSCUTANEOUS AURICULAR-NERVE STIMULATION MEASURED IN A SUBJECT WITH ANGINA PECTORIS

We have measured the short-term effects of selective, transcutaneous, auricular-nerve stimulation (tANS) on the heart function, respiratory function, thermal function and galvanic skin response in a patient with angina pectoris with respect to four predefined sites on the left and right cymba concae (CC). The tANS involved the use of a train of monopolar, current, biphasic pulses composed of rectangular cathodic ic and anodic phases ia and globule-like platinum stimulating electrodes. The parameters of the stimulating pulses were as follows: frequency f = 45.5 Hz, cathodic phase width tc = 200 µs, anodic phase width ta = 200 µs, interphase delay d =180 µs, pulse-train duration 2.0 s and time gap between pulse trains 1.0 s. The results show that tANS at predefined sites on the CC produce measurable effects on the assessed vital functions. In conclusion, tANS witbih an increased number of channels, has the potential to be used in the treatment of certain disorders.

Bioacoustic characterization of mating calls of a freshwater fish (Prochilodus magdalenae) for passive acoustic monitoring

Fish produce sounds that are usually species-specific and associated with particular behaviors and contexts. Acoustic characterization enables the use of sounds as natural acoustic labels for species identification. Males of Prochilodus magdalenae produce mating sounds. We characterized these sounds and tested their use in natural habitats, to use passive acoustic monitoring for spawning ground identification. We identified two types of acoustic signals: simple pulses and pulse trains. Simple pulses were 13.7 ms long, with peak frequency of 365 Hz, whereas pulse train were 2.3 s long, had peak frequency of 399 Hz, 48.6 pulses and its pulses lasted 12.2 ms, with interpulse interval of 49.0 ms long and 22.3 Hz pulse rate. We did not detect spawning in absence of male calls nor differences in male sounds at different female densities. We found differences in train duration, pulse rate, and pulse duration in trains, according to the fish's source sites, but these sites were not well discriminated based on bioacoustical variables. In rivers, we located two P. magdalenae spawning grounds and recognized calls from another fish species (Megaleporinus muyscorum). We did not find a significant relationship between fish size and call peak frequency for P. magdalenae.

160 Optimizing TMS Treatment for Depression - The 19 Minute Dash™ Protocol

TitleOptimizing TMS treatment for Depression - The 19 Minute Dash™ protocolObjectiveNeuroStar transcranial magnetic stimulation (TMS) is an effective treatment for patients with major depressive disorder. Due to the treatment session duration, a reduced treatment time would promote patients’ comfort and convenience. Also, shorter treatment sessions of retained efficacy and safety would increase access to treatment. This reduction could be accomplished by decreasing the time between TMS pulse sequences, the intertrain interval (ITI).MethodsMeta-analysis of TMS delivered using varying treatment parameters, particularly the ratio of train duration (“on-time”) to ITI (“off-time”). PubMed and SCOPUS databases were searched through March 30, 2015 using the terms: “transcranial magnetic stimulation”, “TMS”, “rTMS”, “inter-train interval”, “inter-stimulus interval”, and “cortical spread”. Three hundred and one articles were identified comprising a total of 3359 patients. Clinical outcomes were reported as the proportion of patients achieving response defined as 50% reduction in baseline score on the primary outcome measure in each study. Treatment risk was assessed by the frequency of adverse events reported, and specifically considering the incidence of seizures.ResultsThis analysis confirms prior reports that the variables which impact treatment efficacy are the number of treatmentsessions, the number of pulses per session and the percent motor threshold. Varying the train duration/ITI (on-time/off-time) ratio over a broad range from 2.0 to 14 did not impact efficacy or safety.ConclusionsShortening the ITI to 11 seconds does not impact the safety and antidepressant effectiveness of the NeuroStar TMS and would result in shortening of each treatment session from approximately 37.5 to 19 minutes.Funding AcknowledgementsNeuronetics, Inc.

Variability of intraoperative electrostimulation parameters in conscious individuals: language cortex

OBJECTIVEElectrostimulation in awake brain mapping is widely used to guide tumor removal, but methodologies can differ substantially across institutions. The authors studied electrostimulation brain mapping data to characterize the variability of the current intensity threshold across patients and the effect of its variations on the number, type, and surface area of the essential language areas detected.METHODSOver 7 years, the authors prospectively studied 100 adult patients who were undergoing intraoperative brain mapping during resection of left hemisphere tumors. In all 100 cases, the same protocol of electrostimulation brain mapping (a controlled naming task—bipolar stimulation with biphasic square wave pulses of 1-msec duration and 60-Hz trains, maximum train duration 6 sec) and electrocorticography was used to detect essential language areas.RESULTSThe minimum positive thresholds of stimulation varied from patient to patient; the mean minimum intensity required to detect interference was 4.46 mA (range 1.5–9 mA), and in a substantial proportion of sites (13.5%) interference was detected only at intensities above 6 mA. The threshold varied within a given patient for different naming areas in 22% of cases. Stimulation of the same naming area with greater intensities led to slight changes in the type of response in 19% of cases and different types of responses in 4.5%. Naming sites detected were located in subcentimeter cortical areas (50% were less than 20 mm2), but their extent varied with the intensity of stimulation. During a brain mapping session, the same intensity of stimulation reproduced the same type of interference in 94% of the cases. There was no statistically significant difference between the mean stimulation intensities required to produce interfereince in the left inferior frontal lobe (Broca's area), the supramarginal gyri, and the posterior temporal region.CONCLUSIONSIntrasubject and intersubject variations of the minimum thresholds of positive naming areas and changes in the type of response and in the size of these areas according to the intensity used may limit the interpretation of data from electrostimulation in awake brain mapping. To optimize the identification of language areas during electrostimulation brain mapping, it is important to use different intensities of stimulation at the maximum possible currents, avoiding afterdischarges. This could refine the clinical results and scientific data derived from these mapping sessions.

Computational modeling of neurons: intensity-duration relationship of extracellular electrical stimulation for changes in intracellular calcium

In many instances of extensive nerve damage, the injured nerve never adequately heals, leaving lack of nerve function. Electrical stimulation (ES) has been shown to increase the rate and orient the direction of neurite growth, and is a promising therapy. However, the mechanism in which ES affects neuronal growth is not understood, making it difficult to compare existing ES protocols or to design and optimize new protocols. We hypothesize that ES acts by elevating intracellular calcium concentration ([Ca2+]i) via opening voltage-dependent Ca2+ channels (VDCCs). In this work, we have created a computer model to estimate the ES Ca2+ relationship. Using COMSOL Multiphysics, we modeled a small dorsal root ganglion (DRG) neuron that includes one Na+ channel, two K+ channels, and three VDCCs to estimate [Ca2+]i in the soma and growth cone. As expected, the results show that an ES that generates action potentials (APs) can efficiently raise the [Ca2+]i of neurons. More interestingly, our simulation results show that sub-AP ES can efficiently raise neuronal [Ca2+]i and that specific high-voltage ES can preferentially raise [Ca2+]i in the growth cone. The intensities and durations of ES on modeled growth cone calcium rise are consistent with directionality and orientation of growth cones experimentally shown by others. Finally, this model provides a basis to design experimental ES pulse parameters, including duration, intensity, pulse-train frequency, and pulse-train duration to efficiently raise [Ca2+]i in neuronal somas or growth cones.

Behavioral assessment of sensitivity to intracortical microstimulation of primate somatosensory cortex

Intracortical microstimulation (ICMS) is a powerful tool to investigate the functional role of neural circuits and may provide a means to restore sensation for patients for whom peripheral stimulation is not an option. In a series of psychophysical experiments with nonhuman primates, we investigate how stimulation parameters affect behavioral sensitivity to ICMS. Specifically, we deliver ICMS to primary somatosensory cortex through chronically implanted electrode arrays across a wide range of stimulation regimes. First, we investigate how the detectability of ICMS depends on stimulation parameters, including pulse width, frequency, amplitude, and pulse train duration. Then, we characterize the degree to which ICMS pulse trains that differ in amplitude lead to discriminable percepts across the range of perceptible and safe amplitudes. We also investigate how discriminability of pulse amplitude is modulated by other stimulation parameters—namely, frequency and duration. Perceptual judgments obtained across these various conditions will inform the design of stimulation regimes for neuroscience and neuroengineering applications.

Apparent source level of free-ranging humpback dolphin, Sousa chinensis, in the South China Sea

The acoustic performance and behaviour of free-ranging cetaceans requires investigation under natural conditions to understand how wild animals use sound. This is also useful to develop quantitative evaluation techniques for passive acoustic monitoring. There have been limited studies on the acoustics of the Indo-Pacific humpback dolphin; nevertheless, this species is of particular concern because of the anthropogenic activity in the coastal habitats. In the present study, we used a four-hydrophone array to estimate the apparent source levels (ASLs) of biosonar sequences (click trains), of this species in San-Niang Bay, China. As the dolphins approached the array, 173 click trains were found to meet the criteria of on-axis sounds produced within 60 m of the equipment. In total, 121 unclipped click trains were used for the ASL estimation. The qualified click trains contained 36.3 ± 32.5 clicks, lasting for 1.5 ± 1.5 s, with average inter-click intervals (ICIs) of 51.2 ± 38.3 ms. Average ICIs showed a bimodal distribution, with a cut-off at 20 ms. Short-range click trains, with short ICIs of <20 ms on average, were characterized by smaller ASLs, relatively stable ICIs and a shorter click train duration. The mean back-calculated ASL for humpback dolphins with an approximately maximum body size of 2.5 m was 181.7 ± 7.0 dB re 1 μPa at a distance of 1.6–57.2 m. This value was comparable to that recorded for other dolphins of similar body size, although the ASL estimates obtained in this study might be conservative.