5-25Hz Σ Power/sec Threshold (T , mm) 0 0.5 1 0 5 10 15 e Object Localization and Vibrissal Behavior in 3D Per Magne Knutsen, Armin Biess, Maciej Pietr & Ehud Ahissar Departments of Neurobiology and Mathematics, Weizmann Institute of Science, Israel Whisking behavior in 3D We trained rats to discriminate the relative horizontal (posterior-anterior) offset of two vertical poles. Offsets were adjusted according to a staircase procedure, allowing us to estimate psychophysical thresholds. Summary Horizontal object localization Whisker torsion enables labelled-line encoding of horizontal object location Whisker azimuth and torsional rotation Rats can resolve horizontal spatial offsets with hyperacuity resolution, an ability that relies on actively generated whisker movements. The major components of whisking are azimuthal and torsional rotation. These two angles are tightly coupled during whisking, ensuring per- ceptual stability across whisking cycles. Furthermore, the existence of torsion suggests that neurons with different directional selectivity are gradually recruited during active palpation, which enables mapping of contact information onto the circumference of the whisker follicle and a labelled-line code for horizontal object location. High-speed camera Mirror Head bolts Z X z x Y y ϕ θ ζ 0 20 40 -10 10 30 -20 -10 0 Medio-lateral (mm) Rostro-caudal (mm) Dorso-ventral (mm) A B C D E α (dζ/dθ) Whisker Row −1 0 1 R2 = 0.97 A1 B1 C1 D1 E1 = 0.77 (0.77) R2 = 0.74 (0.9) R2 = 0.90 R2 = 0.98 R2 200 ms 40 deg 40 deg θ 40 deg ζ Azimuthal protraction (deg) 0 45 90 135 180 A B C D E Whisker Row A B C D E R(α) Whisker Row 0 0.5 1 0 50 100 150 θ ζ ϕ Angles Amplitude Whisker deflection angle ζ Protraction θ Retraction 0 π -π Follicle orientation Normalized spike-rate Backlit discrimination area Behavioral box Reward well Touch sensor Vertical poles Servo motor IR beam A B C D 1 2 3 4 10mm Offset (mm) Trial number 20 40 1 5 20 0.9 20 2.7 20 40 60 0.5 60 80 100 Angle (deg) 0 250 500 750 50 Time (msec) distance (mm) Nosepoke 0 5 10 15 20 0 50 100 150 Trials Whisks/trial 0 5 10 15 20 0 .25 .5 .75 1 Initial groups After trimming Control groups Sessions (%) 0 5 10 15 20 0 5 10 15 20 0 .25 .5 .75 1 0 .25 .5 .75 1 ALL ARC ROW C2 ROW/ARC-FN ROW-C2-NONE ALL-ARC ALL-ARC-C2 ALL-C2 ARC-C2 ROW-C2 Threshold (T , mm) e,s Threshold (T , mm) e,s Threshold (T , mm) e,s 0 10 20 30 -10 0 10 Radial distance (mm) Horizontal distance (mm) C3 C3 C1 C1 C2 C2 Power/sec (dB/Hz/s) 2 4 6 8 10 .001 .01 .05 1 20 50 5 P-value Frequency (Hz) Whisking frequency (Hz) 0 5 10 15 20 25 0 .05 .1 .15 Probability W The visual system may also employ popula- tions of directionally tuned neurons to encode visual features in a gaze dependent manner. Accuracy of horizontal localization is correlated with whisking power. Spatial acuity depends on whisker configuration Spatial acuity exceeds whisker spacing Horizontal localization is an active process and depends on whisker movement The correlation between torsion and azimuth is reminiscent of Donder's Law in vision, which states that eye torsion is directly related to gaze direction. Such relationships ensure visual/tactile stability across sequential fixations/whisks. Upon contact with an object, the touch signal will be conveyed primarily by a population of primary afferents, whose direc- tional preference coincides with the torsional angle. Reconstructions of whisker movements in 3D using high-speed, stereo videography enabled us to extract 5 degrees of freedom: 3 rotational, and 2 translational movement components. Whiskers undergo torsional rotation (up to 100 deg) during whisking. Torsion was highly cor- related with azimuthal rotations, in a manner consistent for individual whiskers, similar along rows, but systematically varying across rows such that rows A and E counter-rotated. Torsion predicts that neurons with different directional selec- tivity are gradually recruited during active palpation. Thus, tor- sion adds another