Simultaneous acoustic stimulation of human primary and secondary somatosensory cortices using transcranial focused ultrasound - PubMed (original) (raw)

Simultaneous acoustic stimulation of human primary and secondary somatosensory cortices using transcranial focused ultrasound

Wonhye Lee et al. BMC Neurosci. 2016.

Abstract

Background: Transcranial focused ultrasound (FUS) is gaining momentum as a novel non-invasive brain stimulation method, with promising potential for superior spatial resolution and depth penetration compared to transcranial magnetic stimulation or transcranial direct current stimulation. We examined the presence of tactile sensations elicited by FUS stimulation of two separate brain regions in humans-the primary (SI) and secondary (SII) somatosensory areas of the hand, as guided by individual-specific functional magnetic resonance imaging data.

Results: Under image-guidance, acoustic stimulations were delivered to the SI and SII areas either separately or simultaneously. The SII areas were divided into sub-regions that are activated by four types of external tactile sensations to the palmar side of the right hand-vibrotactile, pressure, warmth, and coolness. Across the stimulation conditions (SI only, SII only, SI and SII simultaneously), participants reported various types of tactile sensations that arose from the hand contralateral to the stimulation, such as the palm/back of the hand or as single/neighboring fingers. The type of tactile sensations did not match the sensations that are associated with specific sub-regions in the SII. The neuro-stimulatory effects of FUS were transient and reversible, and the procedure did not cause any adverse changes or discomforts in the subject's mental/physical status.

Conclusions: The use of multiple FUS transducers allowed for simultaneous stimulation of the SI/SII in the same hemisphere and elicited various tactile sensations in the absence of any external sensory stimuli. Stimulation of the SII area alone could also induce perception of tactile sensations. The ability to stimulate multiple brain areas in a spatially restricted fashion can be used to study causal relationships between regional brain activities and their cognitive/behavioral outcomes.

Keywords: Dual transcranial focused ultrasound; Human primary and secondary somatosensory cortices; Image-guidance; Non-invasive brain stimulation; Tactile sensations.

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Figures

Fig. 1

Fig. 1

Experimental schematics of the dual FUS application with the sonication parameters. a Left panel a rendering of the FUS setup, and right panel its actual implementation on a mannequin head model. The two FUS foci were placed at the targeted SI and SII by image-guidance using optical trackers (‘tracker 1’ and ‘tracker 2’) in reference to the subject head (tracked via ‘helmet tracker’). Each tracker had four infrared-reflective markers for real-time motion detection. FUS transducers were actuated by the sinusoidal electrical signals with impedance matching circuits. Compressible hydrogel was used to couple the FUS transducer to the scalp. b Upper panel illustration of the acoustic parameters. SD sonication duration = 500 ms, ISI inter-stimulation-interval = 7 s, TBD tone-burst-duration = 1 ms, PRF pulse-repetition-frequency = 500 Hz; Incident spatial-peak pulse-average intensity = 35.0 W/cm2 Isppa. Lower panel acoustic intensity mapping of the 210 kHz FUS transducer (longitudinal measurement was taken 10 mm from the exit plane of the transducer). The red dotted lines indicate the FWHM of the intensity profile. c, d Exemplar views of the individual-specific neuroimage-guidance for targeting of ipsilateral SI or SII, respectively. The green crosshairs shown in the projection views (i.e., axial, sagittal, and coronal slices) indicates the sonication target, and the thick green line and yellow line represent the orientation of the sonication path and planned path, respectively, connecting the target (red dot) and entry (green dot) points. In the lower right panel, the four colored dots (without the yellow bar) show the locations of anatomical markers used for the neuroimage-registration with the subject. R and L denote right and left, respectively

Fig. 2

Fig. 2

Graphical illustration of the location of tactile sensations. The distinctive locations of the elicited sensations were depicted by semi-transparent purple color overlaid on the palmar and dorsal views of the right hand for each subject (‘h1’ through ‘h10’). The additional locations (i.e., wrist, forearm, elbow, arm, and leg) of the elicited sensations were also shown under the hand illustrations. The left column shows the locations of the responses during the SIFUS condition. The results from the sensation-specific sessions (i.e., ‘vibrotactile’, ‘pressure’, ‘warmth’, and ‘coolness’) were merged on each column of SIIFUS (middle column) and SI/SIIFUS (right column), respectively. The number of occurrences for a set of distinctive locations of a sensation is represented by a color scale (1_–_3). NR non-responsive cases (‘h8’ under the SI/SIIFUS condition and ‘h10’ during all FUS procedures)

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