Modification by focused ultrasound pulses of electrically evoked responses from an in vitro hippocampal preparation
Patricia C. Rinaldi, Joie P. Jones, Frederick Reines, LeRoy R. Price
Brain Research 1991, 558, 36-42 · 10.1016/0006-8993(91)90711-4
Abstract
The application of short pulses of focused ultrasound was studied as a method of modifying electrically evoked responses in the mammalian brain. The in vitro hippocampal preparation was employed to facilitate delivery and dosimetry of ultrasound, and assessment of mechanisms of ultrasound effects. Cellular and dendritic field potential responses evoked by electrical stimulation of the Schaffer/Commissural afferents were examined before, during and after exposure of a portion of the CA1 region to focused ultrasound pulses for periods ranging from 2 to 15 min. Focused ultrasound with a repetition rate of 150 kHz was delivered in pulses comparable in duration to an electrical pulse that could initiate activity in the nervous system. The pulses had a center frequency of 750 kHz, durations of about 6 microseconds, and spatial-peak-temporal-averaged intensities of about 80 W/cm2. These parameters are markedly different from those employed in conventional diagnostic ultrasound. Temperatures in the bath and tissue were monitored. Extracellular field potentials reflecting the presynaptic fiber volley, dendritic response and cellular discharge were significantly reduced by exposure to ultrasound. Recovery occurred to varying degrees, and in one experiment was complete. Average temperature changes observed were less than 1 degree C. The present study demonstrates that the electrically evoked response in mammalian brain can be altered by ultrasound in a non-thermal, non-cavitational mode, and that such effects are potentially reversible.
Abstract via europepmc.
Exposures
Exposure 1: Focused ultrasound pulses to the CA1 region of the in vitro hippocampal slice
Target: CA1 — “CA1 region”
Device: other named manufacturer · Harisonics Corp. ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 750 | ✓✓✓ |
| Pulse duration (ms) | 0.006 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 150,000 | ✓✓✓⚑ |
| Duty cycle (%) | not reportedpulse duration × PRF gives 90% | |
| Sonication duration (s) | 120, 900swept | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | 82 | ✓✓✓⚑ |
| 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 |
A 750 kHz focused transducer delivered repeated ~6 microsecond acoustic pulses (generated from 100 ns electrical voltage spikes) at a pulse repetition rate of 150 kHz to a small region of the CA1 hippocampal slice, continuously for periods of 2 to 15 min (mean 9.4 min for the fiber-volley experiments; mean 7 min for the dendritic-potential experiments), while electrical stimulation of the Schaffer/Commissural afferents was delivered once every 20 s throughout baseline, ultrasound exposure, and (in some experiments) a recovery period.
Flags from extraction
exposures[0].timing.pulse_repetition_frequency_hz— A stated pulse repetition rate of 150 kHz together with a ~6 microsecond pulse duration implies pulses repeating almost back-to-back (~90% duty cycle), which is unusual for a device described as delivering discrete 'pulses'; the paper does not reconcile this, so the stated PRF is recorded as-is without independently computing a duty cycle.exposures[0].free_field.ispta_w_cm2— The Methods state the calibrated ISPTA is 'no greater than 82 W/cm2', while the Abstract restates this as 'about 80 W/cm2'; the more precise Methods value (82) is recorded here.n_subjects— Reported as the four per-set experiment counts (6, 6, 1, 9); the paper never states a combined total number of slice preparations used.