Figure 4. Axons Exhibit a Diversity of Angular Tuning Profiles Relative to Location of Endings and Preferred Angle.

(A) Responses of 11 identified Merkel afferents to deflections in four directions with respect to the laboratory frame (up, forward, back, and down). All subplots are rotated to place the mechanoreceptor (black dot) at the same angular location, permitting results from all afferents to be overlaid. Pink and cyan vectors indicate ON and OFF response magnitudes for the four deflection directions. For afferent 2, one pair of overlapping pink and cyan vectors is rotated approximately ±5° from nominal for visual clarity.

(B) Angular tuning curves for six unidentified, slowly adapting primary afferents during whisker deflections in either 32 or 16 different directions. Pink/cyan polar plots indicate ON/OFF response magnitudes, respectively.

(C) For Merkel neurons, mechanoreceptor angular locations were well predicted by a cosine function.

(D)Responses of ten identified lanceolate and club-like neurons to deflections in four directions. Conventions are as in (A). For afferents 12 and 16, one pair of overlapping pink and cyan vectors is rotated approximately ±5° from nominal for visual clarity. Two pairs are similarly rotated for afferent 19.

(E)For lanceolate and club-like neurons, mechanoreceptor angular locations were not well predicted by cosine fits.

(F)Relationships between response latency and magnitude (number of spikes/10-ms ON or OFF window) are variable.

See also Figure S4.