Transcranial focused ultrasound modulates the activity of primary somatosensory cortex in humans

Abstract

Improved methods of noninvasively modulating human brain function are needed. Here we probed the influence of transcranial focused ultrasound (tFUS) targeted to the human primary somatosensory cortex (S1) on sensory-evoked brain activity and sensory discrimination abilities. The lateral and axial spatial resolution of the tFUS beam implemented were 4.9 mm and 18 mm, respectively. Electroencephalographic recordings showed that tFUS significantly attenuated the amplitudes of somatosensory evoked potentials elicited by median nerve stimulation. We also found that tFUS significantly modulated the spectral content of sensory-evoked brain oscillations. The changes produced by tFUS on sensory-evoked brain activity were abolished when the acoustic beam was focused 1 cm anterior or posterior to S1. Behavioral investigations showed that tFUS targeted to S1 enhanced performance on sensory discrimination tasks without affecting task attention or response bias. We conclude that tFUS can be used to focally modulate human cortical function.

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Figure 1: Ultrasound can be focused through human skull bone.
Figure 2: tFUS can be targeted to spatially discrete regions of human cortex.
Figure 3: tFUS targeted to human somatosensory cortex modulates sensory-evoked brain activity.
Figure 4: The influence of tFUS on brain activity is not cumulative and remains stable across time.
Figure 5: tFUS targeted to somatosensory cortex enhances sensory discrimination abilities in humans.
Figure 6: tFUS produces differential effects on sensory-evoked activity as a function of the brain region targeted.

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Acknowledgements

Funding and equipment for this study was provided by a Technological Innovation Award from the McKnight Endowment for Neuroscience, Neurotrek, Inc. and the Virginia Tech Carilion Research Institute.

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Contributions

W.L., T.F.S., A.O., J.M., A.B., A.W. and W.J.T. performed the experiments; W.L., T.F.S., A.O. and W.J.T. wrote the manuscript; W.L., T.F.S., A.O. and W.J.T. conducted the data analyses; W.J.T. supervised the project.

Corresponding author

Correspondence to William J Tyler.

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Competing interests

W.J.T. is the cofounder of a medical device company. W.J.T., T.F.S. and A.O. are inventors on patent applications describing methods and devices for noninvasive brain stimulation.

Integrated supplementary information

Supplementary Figure 1 Schematic outline of experimental approach.

a, The FUS transducer is shown placed at EEG electrode site CP3 on a realistic finite element model of a human head (left). A top-down schematic (right) illustrates transducer and electrode positioning at international 10-20 EEG electrode site sites C1, CP1, CP5 and P3. b, The timing strategy for delivering transcranial focused ultrasound (tFUS) or sham prior to, during, and following median nerve stimulation (MN stim) is illustrated. c, A schematic illustrates the pulsed ultrasound (US) waveform transmitted from the focused ultrasound transducer. The acoustic frequency of the waveform was 0.5 MHz and the pulse duration was 360 usec (black). The pulse repetition frequency (PRF; red) was 1 kHz for the stimulation duration of 500 msec.

Supplementary Figure 2 Transcranial focused ultrasound does not affect task attention or response bias on somatosensory discrimination tasks.

a, Data acquired under sham (white) and tFUS (grey) treatments during two-point discrimination testing. The average percent correct for control catch trials (one pin) are illustrated as histograms (top). The criterion (c) data are illustrated as box plots (bottom) where the central line is the median and the edges of the box are the 25th and 75th percentiles with whiskers extending to the extreme data points. b, Data acquired under sham (white) and tFUS (grey) treatments during frequency discrimination testing. The average percent correct for control catch trials (no frequency difference between paired air puff stimuli) are illustrated as histograms (top). The criterion (c) data are illustrated as box plots (bottom) where the central line is the median and the edges of the box are the 25th and 75th percentiles with whiskers extending to the extreme data points.

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Supplementary Figures 1 and 2 and Supplementary Tables 1–3 (PDF 591 kb)

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Legon, W., Sato, T., Opitz, A. et al. Transcranial focused ultrasound modulates the activity of primary somatosensory cortex in humans. Nat Neurosci 17, 322–329 (2014). https://doi.org/10.1038/nn.3620

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