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. 2017 Jun 1;169(6):1029–1041.e16. doi: 10.1016/j.cell.2017.05.024

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© 2017 The Authors

This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

PMC Copyright notice

Application of TI to Steerable Probing of Mouse Motor Cortex Functionality

(A) Currents $I_{1}$ and $I_{2}$ were applied simultaneously (0.5 s ramp-up, 6 s stimulation, 0.5 s ramp-down) to anesthetized head-fixed mice and motor activity was video-recorded (including 1.5 s pre-stimulation and post-stimulation periods). Current $I_{1}$ was applied via a 1 mm diameter skull electrode (white circle; relative to bregma, AP −1.5 mm, ML +2 mm, n = 5 mice; or AP −1.5 mm, ML −2 mm, n = 4 mice) paired with a 5-8 mm diameter electrode (white ellipse). Current $I_{2}$ was applied via a similarly sized skull electrode (black circle; relative to bregma, AP −1.5 mm, ML −0.5 mm, n = 5 mice; or AP −1.5 mm, ML +0.5 mm, n = 4 mice) paired with a 5-8 mm diameter electrode (black ellipse).

(B and C) Characterization of motor threshold. Current ratio $I_{1} : I_{2}$ was fixed at 1:4. Shown is mean motor threshold ± SD (n = 6 mice). Significance calculated using one-way ANOVA followed by post-hoc test with Bonferroni correction for multiple comparisons.

(B) Comparison of motor thresholds with TI stimulation at different difference frequencies and a fixed 2 kHz carrier frequency; p = 0.88; see Table S4 for full statistics for (B).

(C) Comparison of motor thresholds with TI stimulation at different carrier frequencies and fixed 10 Hz difference frequency; ^∗p < 0.05, ^∗∗p < 0.0005; see Table S4 for full statistics for (C).

(D–F) Steerable motor cortex activation. Current $I_{1}$ at a frequency of 1 kHz and current $I_{2}$ at a frequency of 1.01 kHz were applied at different amplitude ratios $I_{1} : I_{2}$ but with a fixed current sum $I_{1} + I_{2}$ (776 μA ± 167 μA; mean ± SD; n = 9 mice).

(D) Evoked movements of the forepaws.

(E) Evoked movements of the whiskers.

(F) Evoked movements of the ears. (i) Number of animals, out of a total of 9 animals, in which the TI stimulation with $I_{1} : I_{2}$ current ratios of 1:2, 1:4 or 1:8 (‘ $I_{1} < I_{2}$ ’), and with $I_{1} : I_{2}$ current ratios of 2:1, 4:1 or 8:1 (‘ $I_{1} > I_{2}$ ’) evoked a movement ipsilateral to $I_{1}$ electrode (white) or contralateral to $I_{1}$ electrode (gray). Significance of number of responders was characterized using Fisher’s exact test; ^∗p < 0.05, ^∗∗p < 0.005, ^∗∗∗p < 0.00001. See Table S4 for full statistics. (ii) Evoked movements ipsilateral to $I_{1}$ electrode (white) and contralateral to $I_{1}$ electrode (gray) at different current ratios $I_{1} : I_{2}$ . Shown values are mean ± SEM; n = 9 mice. Ear movements were visually scored on the following scale: 0, no movement; 1, weak movement; 2, strong movement; 3, very strong movement. Significance of evoked movement for each current ratio was characterized using an unpaired t test versus null hypothesis of no movement, thresholding at p < 0.0025, Bonferroni corrected for multiple comparisons; ^∗p < 0.0025, ^∗∗p < 0.00001; significance between current ratios was calculated using one-way ANOVA followed by post hoc test with Bonferroni correction for multiple comparisons; ^∗p < 0.05. See Table S4 for full statistics.