Precise Neural Stimulation in the Retina Using Focused Ultrasound
Michael D. Menz, Ömer Oralkan, Pierre T. Khuri-Yakub, Stephen A. Baccus
The Journal of Neuroscience 2013, 33, 4550-4560 · 10.1523/jneurosci.3521-12.2013
Abstract
Focused ultrasound is a promising noninvasive technology for neural stimulation. Here we use the isolated salamander retina to characterize the effect of ultrasound on an intact neural circuit and compared these effects with those of visual stimulation of the same retinal ganglion cells. Ultrasound stimuli at an acoustic frequency of 43 MHz and a focal spot diameter of 90 μm delivered from a piezoelectric transducer evoked stable responses with a temporal precision equal to strong visual responses but with shorter latency. By presenting ultrasound and visual stimulation together, we found that ultrasonic stimulation rapidly modulated visual sensitivity but did not change visual temporal filtering. By combining pharmacology with ultrasound stimulation, we found that ultrasound did not directly activate retinal ganglion cells but did in part activate interneurons beyond photoreceptors. These results suggest that, under conditions of strong localized stimulation, timing variability is largely influenced by cells beyond photoreceptors. We conclude that ultrasonic stimulation is an effective and spatiotemporally precise method to activate the retina. Because the retina is the most accessible part of the CNS in vivo, ultrasonic stimulation may have diagnostic potential to probe remaining retinal function in cases of photoreceptor degeneration, and therapeutic potential for use in a retinal prosthesis. In addition, because of its noninvasive properties and spatiotemporal resolution, ultrasound neurostimulation promises to be a useful tool to understand dynamic activity in pharmacologically defined neural pathways in the retina.
Abstract via europepmc.
Exposures
Exposure 1: Focused ultrasound stimulation of the isolated salamander retina at 43 MHz
Target: retina — “the isolated retina”
Device: custom-built
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 43,000 | ✓✓✓ |
| Pulse duration (ms) | 1,000 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 0.5, 15swept | ✓✓✓ |
| Duty cycle (%) | 50 | ✓✓✓ |
| Sonication duration (s) | 60, 300swept | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not applicable | |
| In-situ pressure (kPa) | not applicable | |
| In-situ Isppa (W/cm²) | not applicable | |
| In-situ Ispta (W/cm²) | not applicable | |
| Ispta, domain unspecified (W/cm²) | 0.03, 30, 180swept | ✓✓✓⚑ |
For most experiments, this consisted of 1 s of stimulus On and 1 s of stimulus Off, repeated for many cycles, for a total duration of 1-5 min. In some experiments, the On and Off times were varied randomly to make a binary noise stimulus sampled at 30 Hz to match the temporal structure of visual stimuli. High-frequency sub-modulation of the 43 MHz carrier within each On pulse (10 Hz to 1 MHz) was tested and found to have no effect on responses when average power was held constant, so it was eliminated in favor of a continuous carrier for the On period.
Consistency checks: f0 out of range.
Flags from extraction
exposures[0].unspecified_domain.ispta_w_cm2— The paper states 'time-averaged acoustic power' calculated from an insertion-loss calibration curve (measured in a water bath, not explicitly labelled free-field or in-situ), so the value is placed in unspecified_domain; recorded under ispta_w_cm2 though spatial averaging (peak vs average) is not specified.exposures[0].unspecified_domain.ispta_w_cm2— 180 W/cm2 was the maximum power used in a separate CdCl2 synaptic-block experiment ('The stimulus was repeated at progressively higher-power levels up to 180 W/cm2'), included in the list alongside the main 0.03-30 W/cm2 sweep.n_subjects— The paper reports numbers of cells analysed per figure/comparison but never states the total number of retinas or salamanders used.direction_of_effect— Effects were mixed: direct excitatory spiking responses to US onset/offset, plus bidirectional (increase or decrease) modulation of visual sensitivity depending on distance from the US focus and On vs Off timing.